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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
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*
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package java.lang.invoke;
import java.lang.reflect.*;
import sun.invoke.WrapperInstance;
import sun.invoke.util.ValueConversions;
import sun.invoke.util.VerifyAccess;
import sun.invoke.util.Wrapper;
import java.util.List;
import java.util.ArrayList;
import java.util.Arrays;
import sun.reflect.Reflection;
import static java.lang.invoke.MethodHandleStatics.*;
import static java.lang.invoke.MethodHandleNatives.Constants.*;
/**
* This class consists exclusively of static methods that operate on or return
* method handles. They fall into several categories:
* <ul>
* <li>Lookup methods which help create method handles for methods and fields.
* <li>Combinator methods, which combine or transform pre-existing method handles into new ones.
* <li>Other factory methods to create method handles that emulate other common JVM operations or control flow patterns.
* <li>Wrapper methods which can convert between method handles and interface types.
* </ul>
* <p>
* @author John Rose, JSR 292 EG
*/
public class MethodHandles {
private MethodHandles() { } // do not instantiate
private static final MemberName.Factory IMPL_NAMES = MemberName.getFactory();
static { MethodHandleImpl.initStatics(); }
// See IMPL_LOOKUP below.
//// Method handle creation from ordinary methods.
/**
* Returns a {@link Lookup lookup object} on the caller,
* which has the capability to access any method handle that the caller has access to,
* including direct method handles to private fields and methods.
* This lookup object is a <em>capability</em> which may be delegated to trusted agents.
* Do not store it in place where untrusted code can access it.
*/
public static Lookup lookup() {
return new Lookup();
}
/**
* Returns a {@link Lookup lookup object} which is trusted minimally.
* It can only be used to create method handles to
* publicly accessible fields and methods.
* <p>
* As a matter of pure convention, the {@linkplain Lookup#lookupClass lookup class}
* of this lookup object will be {@link java.lang.Object}.
* <p>
* The lookup class can be changed to any other class {@code C} using an expression of the form
* {@linkplain Lookup#in <code>publicLookup().in(C.class)</code>}.
* Since all classes have equal access to public names,
* such a change would confer no new access rights.
*/
public static Lookup publicLookup() {
return Lookup.PUBLIC_LOOKUP;
}
/**
* A <em>lookup object</em> is a factory for creating method handles,
* when the creation requires access checking.
* Method handles do not perform
* access checks when they are called, but rather when they are created.
* Therefore, method handle access
* restrictions must be enforced when a method handle is created.
* The caller class against which those restrictions are enforced
* is known as the {@linkplain #lookupClass lookup class}.
* <p>
* A lookup class which needs to create method handles will call
* {@link MethodHandles#lookup MethodHandles.lookup} to create a factory for itself.
* When the {@code Lookup} factory object is created, the identity of the lookup class is
* determined, and securely stored in the {@code Lookup} object.
* The lookup class (or its delegates) may then use factory methods
* on the {@code Lookup} object to create method handles for access-checked members.
* This includes all methods, constructors, and fields which are allowed to the lookup class,
* even private ones.
* <p>
* The factory methods on a {@code Lookup} object correspond to all major
* use cases for methods, constructors, and fields.
* Here is a summary of the correspondence between these factory methods and
* the behavior the resulting method handles:
* <code>
* <table border=1 cellpadding=5 summary="lookup method behaviors">
* <tr><th>lookup expression</th><th>member</th><th>behavior</th></tr>
* <tr>
* <td>{@linkplain java.lang.invoke.MethodHandles.Lookup#findGetter lookup.findGetter(C.class,"f",FT.class)}</td>
* <td>FT f;</td><td>(T) this.f;</td>
* </tr>
* <tr>
* <td>{@linkplain java.lang.invoke.MethodHandles.Lookup#findStaticGetter lookup.findStaticGetter(C.class,"f",FT.class)}</td>
* <td>static<br>FT f;</td><td>(T) C.f;</td>
* </tr>
* <tr>
* <td>{@linkplain java.lang.invoke.MethodHandles.Lookup#findSetter lookup.findSetter(C.class,"f",FT.class)}</td>
* <td>FT f;</td><td>this.f = x;</td>
* </tr>
* <tr>
* <td>{@linkplain java.lang.invoke.MethodHandles.Lookup#findStaticSetter lookup.findStaticSetter(C.class,"f",FT.class)}</td>
* <td>static<br>FT f;</td><td>C.f = arg;</td>
* </tr>
* <tr>
* <td>{@linkplain java.lang.invoke.MethodHandles.Lookup#findVirtual lookup.findVirtual(C.class,"m",MT)}</td>
* <td>T m(A*);</td><td>(T) this.m(arg*);</td>
* </tr>
* <tr>
* <td>{@linkplain java.lang.invoke.MethodHandles.Lookup#findStatic lookup.findStatic(C.class,"m",MT)}</td>
* <td>static<br>T m(A*);</td><td>(T) C.m(arg*);</td>
* </tr>
* <tr>
* <td>{@linkplain java.lang.invoke.MethodHandles.Lookup#findSpecial lookup.findSpecial(C.class,"m",MT,this.class)}</td>
* <td>T m(A*);</td><td>(T) super.m(arg*);</td>
* </tr>
* <tr>
* <td>{@linkplain java.lang.invoke.MethodHandles.Lookup#findConstructor lookup.findConstructor(C.class,MT)}</td>
* <td>C(A*);</td><td>(T) new C(arg*);</td>
* </tr>
* <tr>
* <td>{@linkplain java.lang.invoke.MethodHandles.Lookup#unreflectGetter lookup.unreflectGetter(aField)}</td>
* <td>(static)?<br>FT f;</td><td>(FT) aField.get(thisOrNull);</td>
* </tr>
* <tr>
* <td>{@linkplain java.lang.invoke.MethodHandles.Lookup#unreflectSetter lookup.unreflectSetter(aField)}</td>
* <td>(static)?<br>FT f;</td><td>aField.set(thisOrNull, arg);</td>
* </tr>
* <tr>
* <td>{@linkplain java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</td>
* <td>(static)?<br>T m(A*);</td><td>(T) aMethod.invoke(thisOrNull, arg*);</td>
* </tr>
* <tr>
* <td>{@linkplain java.lang.invoke.MethodHandles.Lookup#unreflectConstructor lookup.unreflectConstructor(aConstructor)}</td>
* <td>C(A*);</td><td>(C) aConstructor.newInstance(arg*);</td>
* </tr>
* <tr>
* <td>{@linkplain java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</td>
* <td>(static)?<br>T m(A*);</td><td>(T) aMethod.invoke(thisOrNull, arg*);</td>
* </tr>
* </table>
* </code>
* Here, the type {@code C} is the class or interface being searched for a member,
* documented as a parameter named {@code refc} in the lookup methods.
* The method or constructor type {@code MT} is composed from the return type {@code T}
* and the sequence of argument types {@code A*}.
* Both {@code MT} and the field type {@code FT} are documented as a parameter named {@code type}.
* The formal parameter {@code this} stands for the self-reference of type {@code C};
* if it is present, it is always the leading argument to the method handle invocation.
* The name {@code arg} stands for all the other method handle arguments.
* In the code examples for the Core Reflection API, the name {@code thisOrNull}
* stands for a null reference if the accessed method or field is static,
* and {@code this} otherwise.
* The names {@code aMethod}, {@code aField}, and {@code aConstructor} stand
* for reflective objects corresponding to the given members.
* <p>
* In cases where the given member is of variable arity (i.e., a method or constructor)
* the returned method handle will also be of {@linkplain MethodHandle#asVarargsCollector variable arity}.
* In all other cases, the returned method handle will be of fixed arity.
* <p>
* The equivalence between looked-up method handles and underlying
* class members can break down in a few ways:
* <ul>
* <li>If {@code C} is not symbolically accessible from the lookup class's loader,
* the lookup can still succeed, even when there is no equivalent
* Java expression or bytecoded constant.
* <li>Likewise, if {@code T} or {@code MT}
* is not symbolically accessible from the lookup class's loader,
* the lookup can still succeed.
* For example, lookups for {@code MethodHandle.invokeExact} and
* {@code MethodHandle.invoke} will always succeed, regardless of requested type.
* <li>If there is a security manager installed, it can forbid the lookup
* on various grounds (<a href="#secmgr">see below</a>).
* By contrast, the {@code ldc} instruction is not subject to
* security manager checks.
* </ul>
*
* <h3><a name="access"></a>Access checking</h3>
* Access checks are applied in the factory methods of {@code Lookup},
* when a method handle is created.
* This is a key difference from the Core Reflection API, since
* {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
* performs access checking against every caller, on every call.
* <p>
* All access checks start from a {@code Lookup} object, which
* compares its recorded lookup class against all requests to
* create method handles.
* A single {@code Lookup} object can be used to create any number
* of access-checked method handles, all checked against a single
* lookup class.
* <p>
* A {@code Lookup} object can be shared with other trusted code,
* such as a metaobject protocol.
* A shared {@code Lookup} object delegates the capability
* to create method handles on private members of the lookup class.
* Even if privileged code uses the {@code Lookup} object,
* the access checking is confined to the privileges of the
* original lookup class.
* <p>
* A lookup can fail, because
* the containing class is not accessible to the lookup class, or
* because the desired class member is missing, or because the
* desired class member is not accessible to the lookup class.
* In any of these cases, a {@code ReflectiveOperationException} will be
* thrown from the attempted lookup. The exact class will be one of
* the following:
* <ul>
* <li>NoSuchMethodException — if a method is requested but does not exist
* <li>NoSuchFieldException — if a field is requested but does not exist
* <li>IllegalAccessException — if the member exists but an access check fails
* </ul>
* <p>
* In general, the conditions under which a method handle may be
* looked up for a method {@code M} are exactly equivalent to the conditions
* under which the lookup class could have compiled and resolved a call to {@code M}.
* And the effect of invoking the method handle resulting from the lookup
* is exactly equivalent to executing the compiled and resolved call to {@code M}.
* The same point is true of fields and constructors.
* <p>
* In some cases, access between nested classes is obtained by the Java compiler by creating
* an wrapper method to access a private method of another class
* in the same top-level declaration.
* For example, a nested class {@code C.D}
* can access private members within other related classes such as
* {@code C}, {@code C.D.E}, or {@code C.B},
* but the Java compiler may need to generate wrapper methods in
* those related classes. In such cases, a {@code Lookup} object on
* {@code C.E} would be unable to those private members.
* A workaround for this limitation is the {@link Lookup#in Lookup.in} method,
* which can transform a lookup on {@code C.E} into one on any of those other
* classes, without special elevation of privilege.
* <p>
* Although bytecode instructions can only refer to classes in
* a related class loader, this API can search for methods in any
* class, as long as a reference to its {@code Class} object is
* available. Such cross-loader references are also possible with the
* Core Reflection API, and are impossible to bytecode instructions
* such as {@code invokestatic} or {@code getfield}.
* There is a {@linkplain java.lang.SecurityManager security manager API}
* to allow applications to check such cross-loader references.
* These checks apply to both the {@code MethodHandles.Lookup} API
* and the Core Reflection API
* (as found on {@link java.lang.Class Class}).
* <p>
* Access checks only apply to named and reflected methods,
* constructors, and fields.
* Other method handle creation methods, such as
* {@link MethodHandle#asType MethodHandle.asType},
* do not require any access checks, and are done
* with static methods of {@link MethodHandles},
* independently of any {@code Lookup} object.
*
* <h3>Security manager interactions</h3>
* <a name="secmgr"></a>
* If a security manager is present, member lookups are subject to
* additional checks.
* From one to four calls are made to the security manager.
* Any of these calls can refuse access by throwing a
* {@link java.lang.SecurityException SecurityException}.
* Define {@code smgr} as the security manager,
* {@code refc} as the containing class in which the member
* is being sought, and {@code defc} as the class in which the
* member is actually defined.
* The calls are made according to the following rules:
* <ul>
* <li>In all cases, {@link SecurityManager#checkMemberAccess
* smgr.checkMemberAccess(refc, Member.PUBLIC)} is called.
* <li>If the class loader of the lookup class is not
* the same as or an ancestor of the class loader of {@code refc},
* then {@link SecurityManager#checkPackageAccess
* smgr.checkPackageAccess(refcPkg)} is called,
* where {@code refcPkg} is the package of {@code refc}.
* <li>If the retrieved member is not public,
* {@link SecurityManager#checkMemberAccess
* smgr.checkMemberAccess(defc, Member.DECLARED)} is called.
* (Note that {@code defc} might be the same as {@code refc}.)
* The default implementation of this security manager method
* inspects the stack to determine the original caller of
* the reflective request (such as {@code findStatic}),
* and performs additional permission checks if the
* class loader of {@code defc} differs from the class
* loader of the class from which the reflective request came.
* <li>If the retrieved member is not public,
* and if {@code defc} and {@code refc} are in different class loaders,
* and if the class loader of the lookup class is not
* the same as or an ancestor of the class loader of {@code defc},
* then {@link SecurityManager#checkPackageAccess
* smgr.checkPackageAccess(defcPkg)} is called,
* where {@code defcPkg} is the package of {@code defc}.
* </ul>
*/
public static final
class Lookup {
/** The class on behalf of whom the lookup is being performed. */
private final Class<?> lookupClass;
/** The allowed sorts of members which may be looked up (PUBLIC, etc.). */
private final int allowedModes;
/** A single-bit mask representing {@code public} access,
* which may contribute to the result of {@link #lookupModes lookupModes}.
* The value, {@code 0x01}, happens to be the same as the value of the
* {@code public} {@linkplain java.lang.reflect.Modifier#PUBLIC modifier bit}.
*/
public static final int PUBLIC = Modifier.PUBLIC;
/** A single-bit mask representing {@code private} access,
* which may contribute to the result of {@link #lookupModes lookupModes}.
* The value, {@code 0x02}, happens to be the same as the value of the
* {@code private} {@linkplain java.lang.reflect.Modifier#PRIVATE modifier bit}.
*/
public static final int PRIVATE = Modifier.PRIVATE;
/** A single-bit mask representing {@code protected} access,
* which may contribute to the result of {@link #lookupModes lookupModes}.
* The value, {@code 0x04}, happens to be the same as the value of the
* {@code protected} {@linkplain java.lang.reflect.Modifier#PROTECTED modifier bit}.
*/
public static final int PROTECTED = Modifier.PROTECTED;
/** A single-bit mask representing {@code package} access (default access),
* which may contribute to the result of {@link #lookupModes lookupModes}.
* The value is {@code 0x08}, which does not correspond meaningfully to
* any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
*/
public static final int PACKAGE = Modifier.STATIC;
private static final int ALL_MODES = (PUBLIC | PRIVATE | PROTECTED | PACKAGE);
private static final int TRUSTED = -1;
private static int fixmods(int mods) {
mods &= (ALL_MODES - PACKAGE);
return (mods != 0) ? mods : PACKAGE;
}
/** Tells which class is performing the lookup. It is this class against
* which checks are performed for visibility and access permissions.
* <p>
* The class implies a maximum level of access permission,
* but the permissions may be additionally limited by the bitmask
* {@link #lookupModes lookupModes}, which controls whether non-public members
* can be accessed.
*/
public Class<?> lookupClass() {
return lookupClass;
}
// This is just for calling out to MethodHandleImpl.
private Class<?> lookupClassOrNull() {
return (allowedModes == TRUSTED) ? null : lookupClass;
}
/** Tells which access-protection classes of members this lookup object can produce.
* The result is a bit-mask of the bits
* {@linkplain #PUBLIC PUBLIC (0x01)},
* {@linkplain #PRIVATE PRIVATE (0x02)},
* {@linkplain #PROTECTED PROTECTED (0x04)},
* and {@linkplain #PACKAGE PACKAGE (0x08)}.
* <p>
* A freshly-created lookup object
* on the {@linkplain java.lang.invoke.MethodHandles#lookup() caller's class}
* has all possible bits set, since the caller class can access all its own members.
* A lookup object on a new lookup class
* {@linkplain java.lang.invoke.MethodHandles.Lookup#in created from a previous lookup object}
* may have some mode bits set to zero.
* The purpose of this is to restrict access via the new lookup object,
* so that it can access only names which can be reached by the original
* lookup object, and also by the new lookup class.
*/
public int lookupModes() {
return allowedModes & ALL_MODES;
}
/** Embody the current class (the lookupClass) as a lookup class
* for method handle creation.
* Must be called by from a method in this package,
* which in turn is called by a method not in this package.
* <p>
* Also, don't make it private, lest javac interpose
* an access$N method.
*/
Lookup() {
this(getCallerClassAtEntryPoint(), ALL_MODES);
// make sure we haven't accidentally picked up a privileged class:
checkUnprivilegedlookupClass(lookupClass);
}
Lookup(Class<?> lookupClass) {
this(lookupClass, ALL_MODES);
}
private Lookup(Class<?> lookupClass, int allowedModes) {
this.lookupClass = lookupClass;
this.allowedModes = allowedModes;
}
/**
* Creates a lookup on the specified new lookup class.
* The resulting object will report the specified
* class as its own {@link #lookupClass lookupClass}.
* <p>
* However, the resulting {@code Lookup} object is guaranteed
* to have no more access capabilities than the original.
* In particular, access capabilities can be lost as follows:<ul>
* <li>If the new lookup class differs from the old one,
* protected members will not be accessible by virtue of inheritance.
* (Protected members may continue to be accessible because of package sharing.)
* <li>If the new lookup class is in a different package
* than the old one, protected and default (package) members will not be accessible.
* <li>If the new lookup class is not within the same package member
* as the old one, private members will not be accessible.
* <li>If the new lookup class is not accessible to the old lookup class,
* then no members, not even public members, will be accessible.
* (In all other cases, public members will continue to be accessible.)
* </ul>
*
* @param requestedLookupClass the desired lookup class for the new lookup object
* @return a lookup object which reports the desired lookup class
* @throws NullPointerException if the argument is null
*/
public Lookup in(Class<?> requestedLookupClass) {
requestedLookupClass.getClass(); // null check
if (allowedModes == TRUSTED) // IMPL_LOOKUP can make any lookup at all
return new Lookup(requestedLookupClass, ALL_MODES);
if (requestedLookupClass == this.lookupClass)
return this; // keep same capabilities
int newModes = (allowedModes & (ALL_MODES & ~PROTECTED));
if ((newModes & PACKAGE) != 0
&& !VerifyAccess.isSamePackage(this.lookupClass, requestedLookupClass)) {
newModes &= ~(PACKAGE|PRIVATE);
}
// Allow nestmate lookups to be created without special privilege:
if ((newModes & PRIVATE) != 0
&& !VerifyAccess.isSamePackageMember(this.lookupClass, requestedLookupClass)) {
newModes &= ~PRIVATE;
}
if (newModes == PUBLIC
&& !VerifyAccess.isClassAccessible(requestedLookupClass, this.lookupClass)) {
// The requested class it not accessible from the lookup class.
// No permissions.
newModes = 0;
}
checkUnprivilegedlookupClass(requestedLookupClass);
return new Lookup(requestedLookupClass, newModes);
}
// Make sure outer class is initialized first.
static { IMPL_NAMES.getClass(); }
/** Version of lookup which is trusted minimally.
* It can only be used to create method handles to
* publicly accessible members.
*/
static final Lookup PUBLIC_LOOKUP = new Lookup(Object.class, PUBLIC);
/** Package-private version of lookup which is trusted. */
static final Lookup IMPL_LOOKUP = new Lookup(Object.class, TRUSTED);
private static void checkUnprivilegedlookupClass(Class<?> lookupClass) {
String name = lookupClass.getName();
if (name.startsWith("java.lang.invoke."))
throw newIllegalArgumentException("illegal lookupClass: "+lookupClass);
}
/**
* Displays the name of the class from which lookups are to be made.
* (The name is the one reported by {@link java.lang.Class#getName() Class.getName}.)
* If there are restrictions on the access permitted to this lookup,
* this is indicated by adding a suffix to the class name, consisting
* of a slash and a keyword. The keyword represents the strongest
* allowed access, and is chosen as follows:
* <ul>
* <li>If no access is allowed, the suffix is "/noaccess".
* <li>If only public access is allowed, the suffix is "/public".
* <li>If only public and package access are allowed, the suffix is "/package".
* <li>If only public, package, and private access are allowed, the suffix is "/private".
* </ul>
* If none of the above cases apply, it is the case that full
* access (public, package, private, and protected) is allowed.
* In this case, no suffix is added.
* This is true only of an object obtained originally from
* {@link java.lang.invoke.MethodHandles#lookup MethodHandles.lookup}.
* Objects created by {@link java.lang.invoke.MethodHandles.Lookup#in Lookup.in}
* always have restricted access, and will display a suffix.
* <p>
* (It may seem strange that protected access should be
* stronger than private access. Viewed independently from
* package access, protected access is the first to be lost,
* because it requires a direct subclass relationship between
* caller and callee.)
* @see #in
*/
@Override
public String toString() {
String cname = lookupClass.getName();
switch (allowedModes) {
case 0: // no privileges
return cname + "/noaccess";
case PUBLIC:
return cname + "/public";
case PUBLIC|PACKAGE:
return cname + "/package";
case ALL_MODES & ~PROTECTED:
return cname + "/private";
case ALL_MODES:
return cname;
case TRUSTED:
return "/trusted"; // internal only; not exported
default: // Should not happen, but it's a bitfield...
cname = cname + "/" + Integer.toHexString(allowedModes);
assert(false) : cname;
return cname;
}
}
// call this from an entry point method in Lookup with extraFrames=0.
private static Class<?> getCallerClassAtEntryPoint() {
final int CALLER_DEPTH = 4;
// 0: Reflection.getCC, 1: getCallerClassAtEntryPoint,
// 2: Lookup.<init>, 3: MethodHandles.*, 4: caller
// Note: This should be the only use of getCallerClass in this file.
assert(Reflection.getCallerClass(CALLER_DEPTH-1) == MethodHandles.class);
return Reflection.getCallerClass(CALLER_DEPTH);
}
/**
* Produces a method handle for a static method.
* The type of the method handle will be that of the method.
* (Since static methods do not take receivers, there is no
* additional receiver argument inserted into the method handle type,
* as there would be with {@link #findVirtual findVirtual} or {@link #findSpecial findSpecial}.)
* The method and all its argument types must be accessible to the lookup class.
* If the method's class has not yet been initialized, that is done
* immediately, before the method handle is returned.
* <p>
* The returned method handle will have
* {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
* the method's variable arity modifier bit ({@code 0x0080}) is set.
* @param refc the class from which the method is accessed
* @param name the name of the method
* @param type the type of the method
* @return the desired method handle
* @throws NoSuchMethodException if the method does not exist
* @throws IllegalAccessException if access checking fails,
* or if the method is not {@code static},
* or if the method's variable arity modifier bit
* is set and {@code asVarargsCollector} fails
* @exception SecurityException if a security manager is present and it
* <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
* @throws NullPointerException if any argument is null
*/
public
MethodHandle findStatic(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
MemberName method = resolveOrFail(refc, name, type, true);
checkSecurityManager(refc, method); // stack walk magic: do not refactor
return accessStatic(refc, method);
}
private
MethodHandle accessStatic(Class<?> refc, MemberName method) throws IllegalAccessException {
checkMethod(refc, method, true);
return MethodHandleImpl.findMethod(method, false, lookupClassOrNull());
}
private
MethodHandle resolveStatic(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
MemberName method = resolveOrFail(refc, name, type, true);
return accessStatic(refc, method);
}
/**
* Produces a method handle for a virtual method.
* The type of the method handle will be that of the method,
* with the receiver type (usually {@code refc}) prepended.
* The method and all its argument types must be accessible to the lookup class.
* <p>
* When called, the handle will treat the first argument as a receiver
* and dispatch on the receiver's type to determine which method
* implementation to enter.
* (The dispatching action is identical with that performed by an
* {@code invokevirtual} or {@code invokeinterface} instruction.)
* <p>
* The returned method handle will have
* {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
* the method's variable arity modifier bit ({@code 0x0080}) is set.
* <p>
* Because of the general equivalence between {@code invokevirtual}
* instructions and method handles produced by {@code findVirtual},
* if the class is {@code MethodHandle} and the name string is
* {@code invokeExact} or {@code invoke}, the resulting
* method handle is equivalent to one produced by
* {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker} or
* {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker}
* with the same {@code type} argument.
*
* @param refc the class or interface from which the method is accessed
* @param name the name of the method
* @param type the type of the method, with the receiver argument omitted
* @return the desired method handle
* @throws NoSuchMethodException if the method does not exist
* @throws IllegalAccessException if access checking fails,
* or if the method is {@code static}
* or if the method's variable arity modifier bit
* is set and {@code asVarargsCollector} fails
* @exception SecurityException if a security manager is present and it
* <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
* @throws NullPointerException if any argument is null
*/
public MethodHandle findVirtual(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
MemberName method = resolveOrFail(refc, name, type, false);
checkSecurityManager(refc, method); // stack walk magic: do not refactor
return accessVirtual(refc, method);
}
private MethodHandle resolveVirtual(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
MemberName method = resolveOrFail(refc, name, type, false);
return accessVirtual(refc, method);
}
private MethodHandle accessVirtual(Class<?> refc, MemberName method) throws IllegalAccessException {
checkMethod(refc, method, false);
MethodHandle mh = MethodHandleImpl.findMethod(method, true, lookupClassOrNull());
return restrictProtectedReceiver(method, mh);
}
/**
* Produces a method handle which creates an object and initializes it, using
* the constructor of the specified type.
* The parameter types of the method handle will be those of the constructor,
* while the return type will be a reference to the constructor's class.
* The constructor and all its argument types must be accessible to the lookup class.
* If the constructor's class has not yet been initialized, that is done
* immediately, before the method handle is returned.
* <p>
* Note: The requested type must have a return type of {@code void}.
* This is consistent with the JVM's treatment of constructor type descriptors.
* <p>
* The returned method handle will have
* {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
* the constructor's variable arity modifier bit ({@code 0x0080}) is set.
* @param refc the class or interface from which the method is accessed
* @param type the type of the method, with the receiver argument omitted, and a void return type
* @return the desired method handle
* @throws NoSuchMethodException if the constructor does not exist
* @throws IllegalAccessException if access checking fails
* or if the method's variable arity modifier bit
* is set and {@code asVarargsCollector} fails
* @exception SecurityException if a security manager is present and it
* <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
* @throws NullPointerException if any argument is null
*/
public MethodHandle findConstructor(Class<?> refc, MethodType type) throws NoSuchMethodException, IllegalAccessException {
String name = "<init>";
MemberName ctor = resolveOrFail(refc, name, type, false, false, lookupClassOrNull());
checkSecurityManager(refc, ctor); // stack walk magic: do not refactor
return accessConstructor(refc, ctor);
}
private MethodHandle accessConstructor(Class<?> refc, MemberName ctor) throws IllegalAccessException {
assert(ctor.isConstructor());
checkAccess(refc, ctor);
MethodHandle rawMH = MethodHandleImpl.findMethod(ctor, false, lookupClassOrNull());
MethodHandle allocMH = MethodHandleImpl.makeAllocator(rawMH);
return fixVarargs(allocMH, rawMH);
}
private MethodHandle resolveConstructor(Class<?> refc, MethodType type) throws NoSuchMethodException, IllegalAccessException {
String name = "<init>";
MemberName ctor = resolveOrFail(refc, name, type, false, false, lookupClassOrNull());
return accessConstructor(refc, ctor);
}
/** Return a version of MH which matches matchMH w.r.t. isVarargsCollector. */
private static MethodHandle fixVarargs(MethodHandle mh, MethodHandle matchMH) {
boolean va1 = mh.isVarargsCollector();
boolean va2 = matchMH.isVarargsCollector();
if (va1 == va2) {
return mh;
} else if (va2) {
MethodType type = mh.type();
int arity = type.parameterCount();
return mh.asVarargsCollector(type.parameterType(arity-1));
} else {
return mh.asFixedArity();
}
}
/**
* Produces an early-bound method handle for a virtual method,
* as if called from an {@code invokespecial}
* instruction from {@code caller}.
* The type of the method handle will be that of the method,
* with a suitably restricted receiver type (such as {@code caller}) prepended.
* The method and all its argument types must be accessible
* to the caller.
* <p>
* When called, the handle will treat the first argument as a receiver,
* but will not dispatch on the receiver's type.
* (This direct invocation action is identical with that performed by an
* {@code invokespecial} instruction.)
* <p>
* If the explicitly specified caller class is not identical with the
* lookup class, or if this lookup object does not have private access
* privileges, the access fails.
* <p>
* The returned method handle will have
* {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
* the method's variable arity modifier bit ({@code 0x0080}) is set.
* @param refc the class or interface from which the method is accessed
* @param name the name of the method (which must not be "<init>")
* @param type the type of the method, with the receiver argument omitted
* @param specialCaller the proposed calling class to perform the {@code invokespecial}
* @return the desired method handle
* @throws NoSuchMethodException if the method does not exist
* @throws IllegalAccessException if access checking fails
* or if the method's variable arity modifier bit
* is set and {@code asVarargsCollector} fails
* @exception SecurityException if a security manager is present and it
* <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
* @throws NullPointerException if any argument is null
*/
public MethodHandle findSpecial(Class<?> refc, String name, MethodType type,
Class<?> specialCaller) throws NoSuchMethodException, IllegalAccessException {
checkSpecialCaller(specialCaller);
MemberName method = resolveOrFail(refc, name, type, false, false, specialCaller);
checkSecurityManager(refc, method); // stack walk magic: do not refactor
return accessSpecial(refc, method, specialCaller);
}
private MethodHandle accessSpecial(Class<?> refc, MemberName method,
Class<?> specialCaller) throws NoSuchMethodException, IllegalAccessException {
checkMethod(refc, method, false);
MethodHandle mh = MethodHandleImpl.findMethod(method, false, specialCaller);
return restrictReceiver(method, mh, specialCaller);
}
private MethodHandle resolveSpecial(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
Class<?> specialCaller = lookupClass();
checkSpecialCaller(specialCaller);
MemberName method = resolveOrFail(refc, name, type, false, false, specialCaller);
return accessSpecial(refc, method, specialCaller);
}
/**
* Produces a method handle giving read access to a non-static field.
* The type of the method handle will have a return type of the field's
* value type.
* The method handle's single argument will be the instance containing
* the field.
* Access checking is performed immediately on behalf of the lookup class.
* @param refc the class or interface from which the method is accessed
* @param name the field's name
* @param type the field's type
* @return a method handle which can load values from the field
* @throws NoSuchFieldException if the field does not exist
* @throws IllegalAccessException if access checking fails, or if the field is {@code static}
* @exception SecurityException if a security manager is present and it
* <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
* @throws NullPointerException if any argument is null
*/
public MethodHandle findGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
MemberName field = resolveOrFail(refc, name, type, false);
checkSecurityManager(refc, field); // stack walk magic: do not refactor
return makeAccessor(refc, field, false, false, 0);
}
private MethodHandle resolveGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
MemberName field = resolveOrFail(refc, name, type, false);
return makeAccessor(refc, field, false, false, 0);
}
/**
* Produces a method handle giving write access to a non-static field.
* The type of the method handle will have a void return type.
* The method handle will take two arguments, the instance containing
* the field, and the value to be stored.
* The second argument will be of the field's value type.
* Access checking is performed immediately on behalf of the lookup class.
* @param refc the class or interface from which the method is accessed
* @param name the field's name
* @param type the field's type
* @return a method handle which can store values into the field
* @throws NoSuchFieldException if the field does not exist
* @throws IllegalAccessException if access checking fails, or if the field is {@code static}
* @exception SecurityException if a security manager is present and it
* <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
* @throws NullPointerException if any argument is null
*/
public MethodHandle findSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
MemberName field = resolveOrFail(refc, name, type, false);
checkSecurityManager(refc, field); // stack walk magic: do not refactor
return makeAccessor(refc, field, false, true, 0);
}
private MethodHandle resolveSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
MemberName field = resolveOrFail(refc, name, type, false);
return makeAccessor(refc, field, false, true, 0);
}
/**
* Produces a method handle giving read access to a static field.
* The type of the method handle will have a return type of the field's
* value type.
* The method handle will take no arguments.
* Access checking is performed immediately on behalf of the lookup class.
* @param refc the class or interface from which the method is accessed
* @param name the field's name
* @param type the field's type
* @return a method handle which can load values from the field
* @throws NoSuchFieldException if the field does not exist
* @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
* @exception SecurityException if a security manager is present and it
* <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
* @throws NullPointerException if any argument is null
*/
public MethodHandle findStaticGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
MemberName field = resolveOrFail(refc, name, type, true);
checkSecurityManager(refc, field); // stack walk magic: do not refactor
return makeAccessor(refc, field, false, false, 1);
}
private MethodHandle resolveStaticGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
MemberName field = resolveOrFail(refc, name, type, true);
return makeAccessor(refc, field, false, false, 1);
}
/**
* Produces a method handle giving write access to a static field.
* The type of the method handle will have a void return type.
* The method handle will take a single
* argument, of the field's value type, the value to be stored.
* Access checking is performed immediately on behalf of the lookup class.
* @param refc the class or interface from which the method is accessed
* @param name the field's name
* @param type the field's type
* @return a method handle which can store values into the field
* @throws NoSuchFieldException if the field does not exist
* @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
* @exception SecurityException if a security manager is present and it
* <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
* @throws NullPointerException if any argument is null
*/
public MethodHandle findStaticSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
MemberName field = resolveOrFail(refc, name, type, true);
checkSecurityManager(refc, field); // stack walk magic: do not refactor
return makeAccessor(refc, field, false, true, 1);
}
private MethodHandle resolveStaticSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
MemberName field = resolveOrFail(refc, name, type, true);
return makeAccessor(refc, field, false, true, 1);
}
/**
* Produces an early-bound method handle for a non-static method.
* The receiver must have a supertype {@code defc} in which a method
* of the given name and type is accessible to the lookup class.
* The method and all its argument types must be accessible to the lookup class.
* The type of the method handle will be that of the method,
* without any insertion of an additional receiver parameter.
* The given receiver will be bound into the method handle,
* so that every call to the method handle will invoke the
* requested method on the given receiver.
* <p>
* The returned method handle will have
* {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
* the method's variable arity modifier bit ({@code 0x0080}) is set
* <em>and</em> the trailing array argument is not the only argument.
* (If the trailing array argument is the only argument,
* the given receiver value will be bound to it.)
* <p>
* This is equivalent to the following code:
* <blockquote><pre>
import static java.lang.invoke.MethodHandles.*;
import static java.lang.invoke.MethodType.*;
...
MethodHandle mh0 = lookup().{@link #findVirtual findVirtual}(defc, name, type);
MethodHandle mh1 = mh0.{@link MethodHandle#bindTo bindTo}(receiver);
MethodType mt1 = mh1.type();
if (mh0.isVarargsCollector())
mh1 = mh1.asVarargsCollector(mt1.parameterType(mt1.parameterCount()-1));
return mh1;
* </pre></blockquote>
* where {@code defc} is either {@code receiver.getClass()} or a super
* type of that class, in which the requested method is accessible
* to the lookup class.
* (Note that {@code bindTo} does not preserve variable arity.)
* @param receiver the object from which the method is accessed
* @param name the name of the method
* @param type the type of the method, with the receiver argument omitted
* @return the desired method handle
* @throws NoSuchMethodException if the method does not exist
* @throws IllegalAccessException if access checking fails
* or if the method's variable arity modifier bit
* is set and {@code asVarargsCollector} fails
* @exception SecurityException if a security manager is present and it
* <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
* @throws NullPointerException if any argument is null
*/
public MethodHandle bind(Object receiver, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
Class<? extends Object> refc = receiver.getClass(); // may get NPE
MemberName method = resolveOrFail(refc, name, type, false);
checkSecurityManager(refc, method); // stack walk magic: do not refactor
checkMethod(refc, method, false);
MethodHandle dmh = MethodHandleImpl.findMethod(method, true, lookupClassOrNull());
MethodHandle bmh = MethodHandleImpl.bindReceiver(dmh, receiver);
if (bmh == null)
throw method.makeAccessException("no access", this);
return fixVarargs(bmh, dmh);
}
/**
* Makes a direct method handle to <i>m</i>, if the lookup class has permission.
* If <i>m</i> is non-static, the receiver argument is treated as an initial argument.
* If <i>m</i> is virtual, overriding is respected on every call.
* Unlike the Core Reflection API, exceptions are <em>not</em> wrapped.
* The type of the method handle will be that of the method,
* with the receiver type prepended (but only if it is non-static).
* If the method's {@code accessible} flag is not set,
* access checking is performed immediately on behalf of the lookup class.
* If <i>m</i> is not public, do not share the resulting handle with untrusted parties.
* <p>
* The returned method handle will have
* {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
* the method's variable arity modifier bit ({@code 0x0080}) is set.
* @param m the reflected method
* @return a method handle which can invoke the reflected method
* @throws IllegalAccessException if access checking fails
* or if the method's variable arity modifier bit
* is set and {@code asVarargsCollector} fails
* @throws NullPointerException if the argument is null
*/
public MethodHandle unreflect(Method m) throws IllegalAccessException {
MemberName method = new MemberName(m);
assert(method.isMethod());
if (m.isAccessible())
return MethodHandleImpl.findMethod(method, true, /*no lookupClass*/ null);
checkMethod(method.getDeclaringClass(), method, method.isStatic());
MethodHandle mh = MethodHandleImpl.findMethod(method, true, lookupClassOrNull());
return restrictProtectedReceiver(method, mh);
}
/**
* Produces a method handle for a reflected method.
* It will bypass checks for overriding methods on the receiver,
* as if by a {@code invokespecial} instruction from within the {@code specialCaller}.
* The type of the method handle will be that of the method,
* with the special caller type prepended (and <em>not</em> the receiver of the method).
* If the method's {@code accessible} flag is not set,
* access checking is performed immediately on behalf of the lookup class,
* as if {@code invokespecial} instruction were being linked.
* <p>
* The returned method handle will have
* {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
* the method's variable arity modifier bit ({@code 0x0080}) is set.
* @param m the reflected method
* @param specialCaller the class nominally calling the method
* @return a method handle which can invoke the reflected method
* @throws IllegalAccessException if access checking fails
* or if the method's variable arity modifier bit
* is set and {@code asVarargsCollector} fails
* @throws NullPointerException if any argument is null
*/
public MethodHandle unreflectSpecial(Method m, Class<?> specialCaller) throws IllegalAccessException {
checkSpecialCaller(specialCaller);
MemberName method = new MemberName(m);
assert(method.isMethod());
// ignore m.isAccessible: this is a new kind of access
checkMethod(m.getDeclaringClass(), method, false);
MethodHandle mh = MethodHandleImpl.findMethod(method, false, lookupClassOrNull());
return restrictReceiver(method, mh, specialCaller);
}
/**
* Produces a method handle for a reflected constructor.
* The type of the method handle will be that of the constructor,
* with the return type changed to the declaring class.
* The method handle will perform a {@code newInstance} operation,
* creating a new instance of the constructor's class on the
* arguments passed to the method handle.
* <p>
* If the constructor's {@code accessible} flag is not set,
* access checking is performed immediately on behalf of the lookup class.
* <p>
* The returned method handle will have
* {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
* the constructor's variable arity modifier bit ({@code 0x0080}) is set.
* @param c the reflected constructor
* @return a method handle which can invoke the reflected constructor
* @throws IllegalAccessException if access checking fails
* or if the method's variable arity modifier bit
* is set and {@code asVarargsCollector} fails
* @throws NullPointerException if the argument is null
*/
public MethodHandle unreflectConstructor(Constructor c) throws IllegalAccessException {
MemberName ctor = new MemberName(c);
assert(ctor.isConstructor());
MethodHandle rawCtor;
if (c.isAccessible()) {
rawCtor = MethodHandleImpl.findMethod(ctor, false, /*no lookupClass*/ null);
} else {
checkAccess(c.getDeclaringClass(), ctor);
rawCtor = MethodHandleImpl.findMethod(ctor, false, lookupClassOrNull());
}
MethodHandle allocator = MethodHandleImpl.makeAllocator(rawCtor);
return fixVarargs(allocator, rawCtor);
}
/**
* Produces a method handle giving read access to a reflected field.
* The type of the method handle will have a return type of the field's
* value type.
* If the field is static, the method handle will take no arguments.
* Otherwise, its single argument will be the instance containing
* the field.
* If the field's {@code accessible} flag is not set,
* access checking is performed immediately on behalf of the lookup class.
* @param f the reflected field
* @return a method handle which can load values from the reflected field
* @throws IllegalAccessException if access checking fails
* @throws NullPointerException if the argument is null
*/
public MethodHandle unreflectGetter(Field f) throws IllegalAccessException {
return makeAccessor(f.getDeclaringClass(), new MemberName(f), f.isAccessible(), false, -1);
}
/**
* Produces a method handle giving write access to a reflected field.
* The type of the method handle will have a void return type.
* If the field is static, the method handle will take a single
* argument, of the field's value type, the value to be stored.
* Otherwise, the two arguments will be the instance containing
* the field, and the value to be stored.
* If the field's {@code accessible} flag is not set,
* access checking is performed immediately on behalf of the lookup class.
* @param f the reflected field
* @return a method handle which can store values into the reflected field
* @throws IllegalAccessException if access checking fails
* @throws NullPointerException if the argument is null
*/
public MethodHandle unreflectSetter(Field f) throws IllegalAccessException {
return makeAccessor(f.getDeclaringClass(), new MemberName(f), f.isAccessible(), true, -1);
}
/// Helper methods, all package-private.
MemberName resolveOrFail(Class<?> refc, String name, Class<?> type, boolean isStatic) throws NoSuchFieldException, IllegalAccessException {
checkSymbolicClass(refc); // do this before attempting to resolve
name.getClass(); type.getClass(); // NPE
int mods = (isStatic ? Modifier.STATIC : 0);
return IMPL_NAMES.resolveOrFail(new MemberName(refc, name, type, mods), true, lookupClassOrNull(),
NoSuchFieldException.class);
}
MemberName resolveOrFail(Class<?> refc, String name, MethodType type, boolean isStatic) throws NoSuchMethodException, IllegalAccessException {
checkSymbolicClass(refc); // do this before attempting to resolve
name.getClass(); type.getClass(); // NPE
int mods = (isStatic ? Modifier.STATIC : 0);
return IMPL_NAMES.resolveOrFail(new MemberName(refc, name, type, mods), true, lookupClassOrNull(),
NoSuchMethodException.class);
}
MemberName resolveOrFail(Class<?> refc, String name, MethodType type, boolean isStatic,
boolean searchSupers, Class<?> specialCaller) throws NoSuchMethodException, IllegalAccessException {
checkSymbolicClass(refc); // do this before attempting to resolve
name.getClass(); type.getClass(); // NPE
int mods = (isStatic ? Modifier.STATIC : 0);
return IMPL_NAMES.resolveOrFail(new MemberName(refc, name, type, mods), searchSupers, specialCaller,
NoSuchMethodException.class);
}
void checkSymbolicClass(Class<?> refc) throws IllegalAccessException {
Class<?> caller = lookupClassOrNull();
if (caller != null && !VerifyAccess.isClassAccessible(refc, caller))
throw new MemberName(refc).makeAccessException("symbolic reference class is not public", this);
}
/**
* Perform necessary <a href="MethodHandles.Lookup.html#secmgr">access checks</a>.
* This function performs stack walk magic: do not refactor it.
*/
void checkSecurityManager(Class<?> refc, MemberName m) {
SecurityManager smgr = System.getSecurityManager();
if (smgr == null) return;
if (allowedModes == TRUSTED) return;
// Step 1:
smgr.checkMemberAccess(refc, Member.PUBLIC);
// Step 2:
if (!VerifyAccess.classLoaderIsAncestor(lookupClass, refc))
smgr.checkPackageAccess(VerifyAccess.getPackageName(refc));
// Step 3:
if (m.isPublic()) return;
Class<?> defc = m.getDeclaringClass();
smgr.checkMemberAccess(defc, Member.DECLARED); // STACK WALK HERE
// Step 4:
if (defc != refc)
smgr.checkPackageAccess(VerifyAccess.getPackageName(defc));
// Comment from SM.checkMemberAccess, where which=DECLARED:
/*
* stack depth of 4 should be the caller of one of the
* methods in java.lang.Class that invoke checkMember
* access. The stack should look like:
*
* someCaller [3]
* java.lang.Class.someReflectionAPI [2]
* java.lang.Class.checkMemberAccess [1]
* SecurityManager.checkMemberAccess [0]
*
*/
// For us it is this stack:
// someCaller [3]
// Lookup.findSomeMember [2]
// Lookup.checkSecurityManager [1]
// SecurityManager.checkMemberAccess [0]
}
void checkMethod(Class<?> refc, MemberName m, boolean wantStatic) throws IllegalAccessException {
String message;
if (m.isConstructor())
message = "expected a method, not a constructor";
else if (!m.isMethod())
message = "expected a method";
else if (wantStatic != m.isStatic())
message = wantStatic ? "expected a static method" : "expected a non-static method";
else
{ checkAccess(refc, m); return; }
throw m.makeAccessException(message, this);
}
void checkAccess(Class<?> refc, MemberName m) throws IllegalAccessException {
int allowedModes = this.allowedModes;
if (allowedModes == TRUSTED) return;
int mods = m.getModifiers();
if (Modifier.isPublic(mods) && Modifier.isPublic(refc.getModifiers()) && allowedModes != 0)
return; // common case
int requestedModes = fixmods(mods); // adjust 0 => PACKAGE
if ((requestedModes & allowedModes) != 0
&& VerifyAccess.isMemberAccessible(refc, m.getDeclaringClass(),
mods, lookupClass()))
return;
if (((requestedModes & ~allowedModes) & PROTECTED) != 0
&& VerifyAccess.isSamePackage(m.getDeclaringClass(), lookupClass()))
// Protected members can also be checked as if they were package-private.
return;
throw m.makeAccessException(accessFailedMessage(refc, m), this);
}
String accessFailedMessage(Class<?> refc, MemberName m) {
Class<?> defc = m.getDeclaringClass();
int mods = m.getModifiers();
// check the class first:
boolean classOK = (Modifier.isPublic(defc.getModifiers()) &&
(defc == refc ||
Modifier.isPublic(refc.getModifiers())));
if (!classOK && (allowedModes & PACKAGE) != 0) {
classOK = (VerifyAccess.isClassAccessible(defc, lookupClass()) &&
(defc == refc ||
VerifyAccess.isClassAccessible(refc, lookupClass())));
}
if (!classOK)
return "class is not public";
if (Modifier.isPublic(mods))
return "access to public member failed"; // (how?)
if (Modifier.isPrivate(mods))
return "member is private";
if (Modifier.isProtected(mods))
return "member is protected";
return "member is private to package";
}
private static final boolean ALLOW_NESTMATE_ACCESS = false;
void checkSpecialCaller(Class<?> specialCaller) throws IllegalAccessException {
if (allowedModes == TRUSTED) return;
if ((allowedModes & PRIVATE) == 0
|| (specialCaller != lookupClass()
&& !(ALLOW_NESTMATE_ACCESS &&
VerifyAccess.isSamePackageMember(specialCaller, lookupClass()))))
throw new MemberName(specialCaller).
makeAccessException("no private access for invokespecial", this);
}
MethodHandle restrictProtectedReceiver(MemberName method, MethodHandle mh) throws IllegalAccessException {
// The accessing class only has the right to use a protected member
// on itself or a subclass. Enforce that restriction, from JVMS 5.4.4, etc.
if (!method.isProtected() || method.isStatic()
|| allowedModes == TRUSTED
|| method.getDeclaringClass() == lookupClass()
|| VerifyAccess.isSamePackage(method.getDeclaringClass(), lookupClass())
|| (ALLOW_NESTMATE_ACCESS &&
VerifyAccess.isSamePackageMember(method.getDeclaringClass(), lookupClass())))
return mh;
else
return restrictReceiver(method, mh, lookupClass());
}
MethodHandle restrictReceiver(MemberName method, MethodHandle mh, Class<?> caller) throws IllegalAccessException {
assert(!method.isStatic());
Class<?> defc = method.getDeclaringClass(); // receiver type of mh is too wide
if (defc.isInterface() || !defc.isAssignableFrom(caller)) {
throw method.makeAccessException("caller class must be a subclass below the method", caller);
}
MethodType rawType = mh.type();
if (rawType.parameterType(0) == caller) return mh;
MethodType narrowType = rawType.changeParameterType(0, caller);
MethodHandle narrowMH = MethodHandleImpl.convertArguments(mh, narrowType, rawType, 0);
return fixVarargs(narrowMH, mh);
}
MethodHandle makeAccessor(Class<?> refc, MemberName field,
boolean trusted, boolean isSetter,
int checkStatic) throws IllegalAccessException {
assert(field.isField());
if (checkStatic >= 0 && (checkStatic != 0) != field.isStatic())
throw field.makeAccessException((checkStatic != 0)
? "expected a static field"
: "expected a non-static field", this);
if (trusted)
return MethodHandleImpl.accessField(field, isSetter, /*no lookupClass*/ null);
checkAccess(refc, field);
MethodHandle mh = MethodHandleImpl.accessField(field, isSetter, lookupClassOrNull());
return restrictProtectedReceiver(field, mh);
}
/** Hook called from the JVM (via MethodHandleNatives) to link MH constants:
*/
/*non-public*/
MethodHandle linkMethodHandleConstant(int refKind, Class<?> defc, String name, Object type) throws ReflectiveOperationException {
switch (refKind) {
case REF_getField: return resolveGetter( defc, name, (Class<?>) type );
case REF_getStatic: return resolveStaticGetter( defc, name, (Class<?>) type );
case REF_putField: return resolveSetter( defc, name, (Class<?>) type );
case REF_putStatic: return resolveStaticSetter( defc, name, (Class<?>) type );
case REF_invokeVirtual: return resolveVirtual( defc, name, (MethodType) type );
case REF_invokeStatic: return resolveStatic( defc, name, (MethodType) type );
case REF_invokeSpecial: return resolveSpecial( defc, name, (MethodType) type );
case REF_newInvokeSpecial: return resolveConstructor( defc, (MethodType) type );
case REF_invokeInterface: return resolveVirtual( defc, name, (MethodType) type );
}
// oops
throw new ReflectiveOperationException("bad MethodHandle constant #"+refKind+" "+name+" : "+type);
}
}
/**
* Produces a method handle giving read access to elements of an array.
* The type of the method handle will have a return type of the array's
* element type. Its first argument will be the array type,
* and the second will be {@code int}.
* @param arrayClass an array type
* @return a method handle which can load values from the given array type
* @throws NullPointerException if the argument is null
* @throws IllegalArgumentException if arrayClass is not an array type
*/
public static
MethodHandle arrayElementGetter(Class<?> arrayClass) throws IllegalArgumentException {
return MethodHandleImpl.accessArrayElement(arrayClass, false);
}
/**
* Produces a method handle giving write access to elements of an array.
* The type of the method handle will have a void return type.
* Its last argument will be the array's element type.
* The first and second arguments will be the array type and int.
* @return a method handle which can store values into the array type
* @throws NullPointerException if the argument is null
* @throws IllegalArgumentException if arrayClass is not an array type
*/
public static
MethodHandle arrayElementSetter(Class<?> arrayClass) throws IllegalArgumentException {
return MethodHandleImpl.accessArrayElement(arrayClass, true);
}
/// method handle invocation (reflective style)
/**
* Produces a method handle which will invoke any method handle of the
* given {@code type}, with a given number of trailing arguments replaced by
* a single trailing {@code Object[]} array.
* The resulting invoker will be a method handle with the following
* arguments:
* <ul>
* <li>a single {@code MethodHandle} target
* <li>zero or more leading values (counted by {@code leadingArgCount})
* <li>an {@code Object[]} array containing trailing arguments
* </ul>
* <p>
* The invoker will invoke its target like a call to {@link MethodHandle#invoke invoke} with
* the indicated {@code type}.
* That is, if the target is exactly of the given {@code type}, it will behave
* like {@code invokeExact}; otherwise it behave as if {@link MethodHandle#asType asType}
* is used to convert the target to the required {@code type}.
* <p>
* The type of the returned invoker will not be the given {@code type}, but rather
* will have all parameters except the first {@code leadingArgCount}
* replaced by a single array of type {@code Object[]}, which will be
* the final parameter.
* <p>
* Before invoking its target, the invoker will spread the final array, apply
* reference casts as necessary, and unbox and widen primitive arguments.
* <p>
* This method is equivalent to the following code (though it may be more efficient):
* <p><blockquote><pre>
MethodHandle invoker = MethodHandles.invoker(type);
int spreadArgCount = type.parameterCount() - leadingArgCount;
invoker = invoker.asSpreader(Object[].class, spreadArgCount);
return invoker;
* </pre></blockquote>
* <p>
* This method throws no reflective or security exceptions.
* @param type the desired target type
* @param leadingArgCount number of fixed arguments, to be passed unchanged to the target
* @return a method handle suitable for invoking any method handle of the given type
* @throws NullPointerException if {@code type} is null
* @throws IllegalArgumentException if {@code leadingArgCount} is not in
* the range from 0 to {@code type.parameterCount()} inclusive
*/
static public
MethodHandle spreadInvoker(MethodType type, int leadingArgCount) {
if (leadingArgCount < 0 || leadingArgCount > type.parameterCount())
throw new IllegalArgumentException("bad argument count "+leadingArgCount);
return type.invokers().spreadInvoker(leadingArgCount);
}
/**
* Produces a special <em>invoker method handle</em> which can be used to
* invoke any method handle of the given type, as if by {@link MethodHandle#invokeExact invokeExact}.
* The resulting invoker will have a type which is
* exactly equal to the desired type, except that it will accept
* an additional leading argument of type {@code MethodHandle}.
* <p>
* This method is equivalent to the following code (though it may be more efficient):
* <p><blockquote><pre>
publicLookup().findVirtual(MethodHandle.class, "invokeExact", type)
* </pre></blockquote>
*
* <p style="font-size:smaller;">
* <em>Discussion:</em>
* Invoker method handles can be useful when working with variable method handles
* of unknown types.
* For example, to emulate an {@code invokeExact} call to a variable method
* handle {@code M}, extract its type {@code T},
* look up the invoker method {@code X} for {@code T},
* and call the invoker method, as {@code X.invoke(T, A...)}.
* (It would not work to call {@code X.invokeExact}, since the type {@code T}
* is unknown.)
* If spreading, collecting, or other argument transformations are required,
* they can be applied once to the invoker {@code X} and reused on many {@code M}
* method handle values, as long as they are compatible with the type of {@code X}.
* <p>
* <em>(Note: The invoker method is not available via the Core Reflection API.
* An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
* on the declared {@code invokeExact} or {@code invoke} method will raise an
* {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
* <p>
* This method throws no reflective or security exceptions.
* @param type the desired target type
* @return a method handle suitable for invoking any method handle of the given type
*/
static public
MethodHandle exactInvoker(MethodType type) {
return type.invokers().exactInvoker();
}
/**
* Produces a special <em>invoker method handle</em> which can be used to
* invoke any method handle compatible with the given type, as if by {@link MethodHandle#invoke invoke}.
* The resulting invoker will have a type which is
* exactly equal to the desired type, except that it will accept
* an additional leading argument of type {@code MethodHandle}.
* <p>
* Before invoking its target, if the target differs from the expected type,
* the invoker will apply reference casts as
* necessary and box, unbox, or widen primitive values, as if by {@link MethodHandle#asType asType}.
* Similarly, the return value will be converted as necessary.
* If the target is a {@linkplain MethodHandle#asVarargsCollector variable arity method handle},
* the required arity conversion will be made, again as if by {@link MethodHandle#asType asType}.
* <p>
* A {@linkplain MethodType#genericMethodType general method type},
* mentions only {@code Object} arguments and return values.
* An invoker for such a type is capable of calling any method handle
* of the same arity as the general type.
* <p>
* This method is equivalent to the following code (though it may be more efficient):
* <p><blockquote><pre>
publicLookup().findVirtual(MethodHandle.class, "invoke", type)
* </pre></blockquote>
* <p>
* This method throws no reflective or security exceptions.
* @param type the desired target type
* @return a method handle suitable for invoking any method handle convertible to the given type
*/
static public
MethodHandle invoker(MethodType type) {
return type.invokers().generalInvoker();
}
/**
* Perform value checking, exactly as if for an adapted method handle.
* It is assumed that the given value is either null, of type T0,
* or (if T0 is primitive) of the wrapper class corresponding to T0.
* The following checks and conversions are made:
* <ul>
* <li>If T0 and T1 are references, then a cast to T1 is applied.
* (The types do not need to be related in any particular way.)
* <li>If T0 and T1 are primitives, then a widening or narrowing
* conversion is applied, if one exists.
* <li>If T0 is a primitive and T1 a reference, and
* T0 has a wrapper class TW, a boxing conversion to TW is applied,
* possibly followed by a reference conversion.
* T1 must be TW or a supertype.
* <li>If T0 is a reference and T1 a primitive, and
* T1 has a wrapper class TW, an unboxing conversion is applied,
* possibly preceded by a reference conversion.
* T0 must be TW or a supertype.
* <li>If T1 is void, the return value is discarded
* <li>If T0 is void and T1 a reference, a null value is introduced.
* <li>If T0 is void and T1 a primitive, a zero value is introduced.
* </ul>
* If the value is discarded, null will be returned.
* @param valueType
* @param value
* @return the value, converted if necessary
* @throws java.lang.ClassCastException if a cast fails
*/
// FIXME: This is used in just one place. Refactor away.
static
<T0, T1> T1 checkValue(Class<T0> t0, Class<T1> t1, Object value)
throws ClassCastException
{
if (t0 == t1) {
// no conversion needed; just reassert the same type
if (t0.isPrimitive())
return Wrapper.asPrimitiveType(t1).cast(value);
else
return Wrapper.OBJECT.convert(value, t1);
}
boolean prim0 = t0.isPrimitive(), prim1 = t1.isPrimitive();
if (!prim0) {
// check contract with caller
Wrapper.OBJECT.convert(value, t0);
if (!prim1) {
return Wrapper.OBJECT.convert(value, t1);
}
// convert reference to primitive by unboxing
Wrapper w1 = Wrapper.forPrimitiveType(t1);
return w1.convert(value, t1);
}
// check contract with caller:
Wrapper.asWrapperType(t0).cast(value);
Wrapper w1 = Wrapper.forPrimitiveType(t1);
return w1.convert(value, t1);
}
// FIXME: Delete this. It is used only for insertArguments & bindTo.
// Replace by a more standard check.
static
Object checkValue(Class<?> T1, Object value)
throws ClassCastException
{
Class<?> T0;
if (value == null)
T0 = Object.class;
else
T0 = value.getClass();
return checkValue(T0, T1, value);
}
/// method handle modification (creation from other method handles)
/**
* Produces a method handle which adapts the type of the
* given method handle to a new type by pairwise argument and return type conversion.
* The original type and new type must have the same number of arguments.
* The resulting method handle is guaranteed to report a type
* which is equal to the desired new type.
* <p>
* If the original type and new type are equal, returns target.
* <p>
* The same conversions are allowed as for {@link MethodHandle#asType MethodHandle.asType},
* and some additional conversions are also applied if those conversions fail.
* Given types <em>T0</em>, <em>T1</em>, one of the following conversions is applied
* if possible, before or instead of any conversions done by {@code asType}:
* <ul>
* <li>If <em>T0</em> and <em>T1</em> are references, and <em>T1</em> is an interface type,
* then the value of type <em>T0</em> is passed as a <em>T1</em> without a cast.
* (This treatment of interfaces follows the usage of the bytecode verifier.)
* <li>If <em>T0</em> is boolean and <em>T1</em> is another primitive,
* the boolean is converted to a byte value, 1 for true, 0 for false.
* (This treatment follows the usage of the bytecode verifier.)
* <li>If <em>T1</em> is boolean and <em>T0</em> is another primitive,
* <em>T0</em> is converted to byte via Java casting conversion (JLS 5.5),
* and the low order bit of the result is tested, as if by {@code (x & 1) != 0}.
* <li>If <em>T0</em> and <em>T1</em> are primitives other than boolean,
* then a Java casting conversion (JLS 5.5) is applied.
* (Specifically, <em>T0</em> will convert to <em>T1</em> by
* widening and/or narrowing.)
* <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, an unboxing
* conversion will be applied at runtime, possibly followed
* by a Java casting conversion (JLS 5.5) on the primitive value,
* possibly followed by a conversion from byte to boolean by testing
* the low-order bit.
* <li>If <em>T0</em> is a reference and <em>T1</em> a primitive,
* and if the reference is null at runtime, a zero value is introduced.
* </ul>
* @param target the method handle to invoke after arguments are retyped
* @param newType the expected type of the new method handle
* @return a method handle which delegates to the target after performing
* any necessary argument conversions, and arranges for any
* necessary return value conversions
* @throws NullPointerException if either argument is null
* @throws WrongMethodTypeException if the conversion cannot be made
* @see MethodHandle#asType
*/
public static
MethodHandle explicitCastArguments(MethodHandle target, MethodType newType) {
return MethodHandleImpl.convertArguments(target, newType, 2);
}
/**
* Produces a method handle which adapts the calling sequence of the
* given method handle to a new type, by reordering the arguments.
* The resulting method handle is guaranteed to report a type
* which is equal to the desired new type.
* <p>
* The given array controls the reordering.
* Call {@code #I} the number of incoming parameters (the value
* {@code newType.parameterCount()}, and call {@code #O} the number
* of outgoing parameters (the value {@code target.type().parameterCount()}).
* Then the length of the reordering array must be {@code #O},
* and each element must be a non-negative number less than {@code #I}.
* For every {@code N} less than {@code #O}, the {@code N}-th
* outgoing argument will be taken from the {@code I}-th incoming
* argument, where {@code I} is {@code reorder[N]}.
* <p>
* No argument or return value conversions are applied.
* The type of each incoming argument, as determined by {@code newType},
* must be identical to the type of the corresponding outgoing parameter
* or parameters in the target method handle.
* The return type of {@code newType} must be identical to the return
* type of the original target.
* <p>
* The reordering array need not specify an actual permutation.
* An incoming argument will be duplicated if its index appears
* more than once in the array, and an incoming argument will be dropped
* if its index does not appear in the array.
* As in the case of {@link #dropArguments(MethodHandle,int,List) dropArguments},
* incoming arguments which are not mentioned in the reordering array
* are may be any type, as determined only by {@code newType}.
* <blockquote><pre>
import static java.lang.invoke.MethodHandles.*;
import static java.lang.invoke.MethodType.*;
...
MethodType intfn1 = methodType(int.class, int.class);
MethodType intfn2 = methodType(int.class, int.class, int.class);
MethodHandle sub = ... {int x, int y => x-y} ...;
assert(sub.type().equals(intfn2));
MethodHandle sub1 = permuteArguments(sub, intfn2, 0, 1);
MethodHandle rsub = permuteArguments(sub, intfn2, 1, 0);
assert((int)rsub.invokeExact(1, 100) == 99);
MethodHandle add = ... {int x, int y => x+y} ...;
assert(add.type().equals(intfn2));
MethodHandle twice = permuteArguments(add, intfn1, 0, 0);
assert(twice.type().equals(intfn1));
assert((int)twice.invokeExact(21) == 42);
* </pre></blockquote>
* @param target the method handle to invoke after arguments are reordered
* @param newType the expected type of the new method handle
* @param reorder an index array which controls the reordering
* @return a method handle which delegates to the target after it
* drops unused arguments and moves and/or duplicates the other arguments
* @throws NullPointerException if any argument is null
* @throws IllegalArgumentException if the index array length is not equal to
* the arity of the target, or if any index array element
* not a valid index for a parameter of {@code newType},
* or if two corresponding parameter types in
* {@code target.type()} and {@code newType} are not identical,
*/
public static
MethodHandle permuteArguments(MethodHandle target, MethodType newType, int... reorder) {
MethodType oldType = target.type();
checkReorder(reorder, newType, oldType);
return MethodHandleImpl.permuteArguments(target,
newType, oldType,
reorder);
}
private static void checkReorder(int[] reorder, MethodType newType, MethodType oldType) {
if (newType.returnType() != oldType.returnType())
throw newIllegalArgumentException("return types do not match",
oldType, newType);
if (reorder.length == oldType.parameterCount()) {
int limit = newType.parameterCount();
boolean bad = false;
for (int j = 0; j < reorder.length; j++) {
int i = reorder[j];
if (i < 0 || i >= limit) {
bad = true; break;
}
Class<?> src = newType.parameterType(i);
Class<?> dst = oldType.parameterType(j);
if (src != dst)
throw newIllegalArgumentException("parameter types do not match after reorder",
oldType, newType);
}
if (!bad) return;
}
throw newIllegalArgumentException("bad reorder array: "+Arrays.toString(reorder));
}
/**
* Produces a method handle of the requested return type which returns the given
* constant value every time it is invoked.
* <p>
* Before the method handle is returned, the passed-in value is converted to the requested type.
* If the requested type is primitive, widening primitive conversions are attempted,
* else reference conversions are attempted.
* <p>The returned method handle is equivalent to {@code identity(type).bindTo(value)}.
* @param type the return type of the desired method handle
* @param value the value to return
* @return a method handle of the given return type and no arguments, which always returns the given value
* @throws NullPointerException if the {@code type} argument is null
* @throws ClassCastException if the value cannot be converted to the required return type
* @throws IllegalArgumentException if the given type is {@code void.class}
*/
public static
MethodHandle constant(Class<?> type, Object value) {
if (type.isPrimitive()) {
if (type == void.class)
throw newIllegalArgumentException("void type");
Wrapper w = Wrapper.forPrimitiveType(type);
return insertArguments(identity(type), 0, w.convert(value, type));
} else {
return identity(type).bindTo(type.cast(value));
}
}
/**
* Produces a method handle which returns its sole argument when invoked.
* @param type the type of the sole parameter and return value of the desired method handle
* @return a unary method handle which accepts and returns the given type
* @throws NullPointerException if the argument is null
* @throws IllegalArgumentException if the given type is {@code void.class}
*/
public static
MethodHandle identity(Class<?> type) {
if (type == void.class)
throw newIllegalArgumentException("void type");
else if (type == Object.class)
return ValueConversions.identity();
else if (type.isPrimitive())
return ValueConversions.identity(Wrapper.forPrimitiveType(type));
else
return AdapterMethodHandle.makeRetypeRaw(
MethodType.methodType(type, type), ValueConversions.identity());
}
/**
* Provides a target method handle with one or more <em>bound arguments</em>
* in advance of the method handle's invocation.
* The formal parameters to the target corresponding to the bound
* arguments are called <em>bound parameters</em>.
* Returns a new method handle which saves away the bound arguments.
* When it is invoked, it receives arguments for any non-bound parameters,
* binds the saved arguments to their corresponding parameters,
* and calls the original target.
* <p>
* The type of the new method handle will drop the types for the bound
* parameters from the original target type, since the new method handle
* will no longer require those arguments to be supplied by its callers.
* <p>
* Each given argument object must match the corresponding bound parameter type.
* If a bound parameter type is a primitive, the argument object
* must be a wrapper, and will be unboxed to produce the primitive value.
* <p>
* The {@code pos} argument selects which parameters are to be bound.
* It may range between zero and <i>N-L</i> (inclusively),
* where <i>N</i> is the arity of the target method handle
* and <i>L</i> is the length of the values array.
* @param target the method handle to invoke after the argument is inserted
* @param pos where to insert the argument (zero for the first)
* @param values the series of arguments to insert
* @return a method handle which inserts an additional argument,
* before calling the original method handle
* @throws NullPointerException if the target or the {@code values} array is null
* @see MethodHandle#bindTo
*/
public static
MethodHandle insertArguments(MethodHandle target, int pos, Object... values) {
int insCount = values.length;
MethodType oldType = target.type();
int outargs = oldType.parameterCount();
int inargs = outargs - insCount;
if (inargs < 0)
throw newIllegalArgumentException("too many values to insert");
if (pos < 0 || pos > inargs)
throw newIllegalArgumentException("no argument type to append");
MethodHandle result = target;
for (int i = 0; i < insCount; i++) {
Object value = values[i];
Class<?> valueType = oldType.parameterType(pos+i);
value = checkValue(valueType, value);
if (pos == 0 && !valueType.isPrimitive()) {
// At least for now, make bound method handles a special case.
MethodHandle bmh = MethodHandleImpl.bindReceiver(result, value);
if (bmh != null) {
result = bmh;
continue;
}
// else fall through to general adapter machinery
}
result = MethodHandleImpl.bindArgument(result, pos, value);
}
return result;
}
/**
* Produces a method handle which will discard some dummy arguments
* before calling some other specified <i>target</i> method handle.
* The type of the new method handle will be the same as the target's type,
* except it will also include the dummy argument types,
* at some given position.
* <p>
* The {@code pos} argument may range between zero and <i>N</i>,
* where <i>N</i> is the arity of the target.
* If {@code pos} is zero, the dummy arguments will precede
* the target's real arguments; if {@code pos} is <i>N</i>
* they will come after.
* <p>
* <b>Example:</b>
* <p><blockquote><pre>
import static java.lang.invoke.MethodHandles.*;
import static java.lang.invoke.MethodType.*;
...
MethodHandle cat = lookup().findVirtual(String.class,
"concat", methodType(String.class, String.class));
assertEquals("xy", (String) cat.invokeExact("x", "y"));
MethodType bigType = cat.type().insertParameterTypes(0, int.class, String.class);
MethodHandle d0 = dropArguments(cat, 0, bigType.parameterList().subList(0,2));
assertEquals(bigType, d0.type());
assertEquals("yz", (String) d0.invokeExact(123, "x", "y", "z"));
* </pre></blockquote>
* <p>
* This method is also equivalent to the following code:
* <p><blockquote><pre>
* {@link #dropArguments(MethodHandle,int,Class...) dropArguments}(target, pos, valueTypes.toArray(new Class[0]))
* </pre></blockquote>
* @param target the method handle to invoke after the arguments are dropped
* @param valueTypes the type(s) of the argument(s) to drop
* @param pos position of first argument to drop (zero for the leftmost)
* @return a method handle which drops arguments of the given types,
* before calling the original method handle
* @throws NullPointerException if the target is null,
* or if the {@code valueTypes} list or any of its elements is null
* @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
* or if {@code pos} is negative or greater than the arity of the target,
* or if the new method handle's type would have too many parameters
*/
public static
MethodHandle dropArguments(MethodHandle target, int pos, List<Class<?>> valueTypes) {
MethodType oldType = target.type(); // get NPE
if (valueTypes.size() == 0) return target;
int outargs = oldType.parameterCount();
int inargs = outargs + valueTypes.size();
if (pos < 0 || pos >= inargs)
throw newIllegalArgumentException("no argument type to remove");
ArrayList<Class<?>> ptypes =
new ArrayList<Class<?>>(oldType.parameterList());
ptypes.addAll(pos, valueTypes);
MethodType newType = MethodType.methodType(oldType.returnType(), ptypes);
return MethodHandleImpl.dropArguments(target, newType, pos);
}
/**
* Produces a method handle which will discard some dummy arguments
* before calling some other specified <i>target</i> method handle.
* The type of the new method handle will be the same as the target's type,
* except it will also include the dummy argument types,
* at some given position.
* <p>
* The {@code pos} argument may range between zero and <i>N</i>,
* where <i>N</i> is the arity of the target.
* If {@code pos} is zero, the dummy arguments will precede
* the target's real arguments; if {@code pos} is <i>N</i>
* they will come after.
* <p>
* <b>Example:</b>
* <p><blockquote><pre>
import static java.lang.invoke.MethodHandles.*;
import static java.lang.invoke.MethodType.*;
...
MethodHandle cat = lookup().findVirtual(String.class,
"concat", methodType(String.class, String.class));
assertEquals("xy", (String) cat.invokeExact("x", "y"));
MethodHandle d0 = dropArguments(cat, 0, String.class);
assertEquals("yz", (String) d0.invokeExact("x", "y", "z"));
MethodHandle d1 = dropArguments(cat, 1, String.class);
assertEquals("xz", (String) d1.invokeExact("x", "y", "z"));
MethodHandle d2 = dropArguments(cat, 2, String.class);
assertEquals("xy", (String) d2.invokeExact("x", "y", "z"));
MethodHandle d12 = dropArguments(cat, 1, int.class, boolean.class);
assertEquals("xz", (String) d12.invokeExact("x", 12, true, "z"));
* </pre></blockquote>
* <p>
* This method is also equivalent to the following code:
* <p><blockquote><pre>
* {@link #dropArguments(MethodHandle,int,List) dropArguments}(target, pos, Arrays.asList(valueTypes))
* </pre></blockquote>
* @param target the method handle to invoke after the arguments are dropped
* @param valueTypes the type(s) of the argument(s) to drop
* @param pos position of first argument to drop (zero for the leftmost)
* @return a method handle which drops arguments of the given types,
* before calling the original method handle
* @throws NullPointerException if the target is null,
* or if the {@code valueTypes} array or any of its elements is null
* @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
* or if {@code pos} is negative or greater than the arity of the target,
* or if the new method handle's type would have too many parameters
*/
public static
MethodHandle dropArguments(MethodHandle target, int pos, Class<?>... valueTypes) {
return dropArguments(target, pos, Arrays.asList(valueTypes));
}
/**
* Adapts a target method handle by pre-processing
* one or more of its arguments, each with its own unary filter function,
* and then calling the target with each pre-processed argument
* replaced by the result of its corresponding filter function.
* <p>
* The pre-processing is performed by one or more method handles,
* specified in the elements of the {@code filters} array.
* The first element of the filter array corresponds to the {@code pos}
* argument of the target, and so on in sequence.
* <p>
* Null arguments in the array are treated as identity functions,
* and the corresponding arguments left unchanged.
* (If there are no non-null elements in the array, the original target is returned.)
* Each filter is applied to the corresponding argument of the adapter.
* <p>
* If a filter {@code F} applies to the {@code N}th argument of
* the target, then {@code F} must be a method handle which
* takes exactly one argument. The type of {@code F}'s sole argument
* replaces the corresponding argument type of the target
* in the resulting adapted method handle.
* The return type of {@code F} must be identical to the corresponding
* parameter type of the target.
* <p>
* It is an error if there are elements of {@code filters}
* (null or not)
* which do not correspond to argument positions in the target.
* <b>Example:</b>
* <p><blockquote><pre>
import static java.lang.invoke.MethodHandles.*;
import static java.lang.invoke.MethodType.*;
...
MethodHandle cat = lookup().findVirtual(String.class,
"concat", methodType(String.class, String.class));
MethodHandle upcase = lookup().findVirtual(String.class,
"toUpperCase", methodType(String.class));
assertEquals("xy", (String) cat.invokeExact("x", "y"));
MethodHandle f0 = filterArguments(cat, 0, upcase);
assertEquals("Xy", (String) f0.invokeExact("x", "y")); // Xy
MethodHandle f1 = filterArguments(cat, 1, upcase);
assertEquals("xY", (String) f1.invokeExact("x", "y")); // xY
MethodHandle f2 = filterArguments(cat, 0, upcase, upcase);
assertEquals("XY", (String) f2.invokeExact("x", "y")); // XY
* </pre></blockquote>
* <p> Here is pseudocode for the resulting adapter:
* <blockquote><pre>
* V target(P... p, A[i]... a[i], B... b);
* A[i] filter[i](V[i]);
* T adapter(P... p, V[i]... v[i], B... b) {
* return target(p..., f[i](v[i])..., b...);
* }
* </pre></blockquote>
*
* @param target the method handle to invoke after arguments are filtered
* @param pos the position of the first argument to filter
* @param filters method handles to call initially on filtered arguments
* @return method handle which incorporates the specified argument filtering logic
* @throws NullPointerException if the target is null
* or if the {@code filters} array is null
* @throws IllegalArgumentException if a non-null element of {@code filters}
* does not match a corresponding argument type of target as described above,
* or if the {@code pos+filters.length} is greater than {@code target.type().parameterCount()}
*/
public static
MethodHandle filterArguments(MethodHandle target, int pos, MethodHandle... filters) {
MethodType targetType = target.type();
MethodHandle adapter = target;
MethodType adapterType = null;
assert((adapterType = targetType) != null);
int maxPos = targetType.parameterCount();
if (pos + filters.length > maxPos)
throw newIllegalArgumentException("too many filters");
int curPos = pos-1; // pre-incremented
for (MethodHandle filter : filters) {
curPos += 1;
if (filter == null) continue; // ignore null elements of filters
adapter = filterArgument(adapter, curPos, filter);
assert((adapterType = adapterType.changeParameterType(curPos, filter.type().parameterType(0))) != null);
}
assert(adapterType.equals(adapter.type()));
return adapter;
}
/*non-public*/ static
MethodHandle filterArgument(MethodHandle target, int pos, MethodHandle filter) {
MethodType targetType = target.type();
MethodType filterType = filter.type();
if (filterType.parameterCount() != 1
|| filterType.returnType() != targetType.parameterType(pos))
throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
return MethodHandleImpl.filterArgument(target, pos, filter);
}
/**
* Adapts a target method handle by post-processing
* its return value (if any) with a filter (another method handle).
* The result of the filter is returned from the adapter.
* <p>
* If the target returns a value, the filter must accept that value as
* its only argument.
* If the target returns void, the filter must accept no arguments.
* <p>
* The return type of the filter
* replaces the return type of the target
* in the resulting adapted method handle.
* The argument type of the filter (if any) must be identical to the
* return type of the target.
* <b>Example:</b>
* <p><blockquote><pre>
import static java.lang.invoke.MethodHandles.*;
import static java.lang.invoke.MethodType.*;
...
MethodHandle cat = lookup().findVirtual(String.class,
"concat", methodType(String.class, String.class));
MethodHandle length = lookup().findVirtual(String.class,
"length", methodType(int.class));
System.out.println((String) cat.invokeExact("x", "y")); // xy
MethodHandle f0 = filterReturnValue(cat, length);
System.out.println((int) f0.invokeExact("x", "y")); // 2
* </pre></blockquote>
* <p> Here is pseudocode for the resulting adapter:
* <blockquote><pre>
* V target(A...);
* T filter(V);
* T adapter(A... a) {
* V v = target(a...);
* return filter(v);
* }
* // and if the target has a void return:
* void target2(A...);
* T filter2();
* T adapter2(A... a) {
* target2(a...);
* return filter2();
* }
* // and if the filter has a void return:
* V target3(A...);
* void filter3(V);
* void adapter3(A... a) {
* V v = target3(a...);
* filter3(v);
* }
* </pre></blockquote>
* @param target the method handle to invoke before filtering the return value
* @param filter method handle to call on the return value
* @return method handle which incorporates the specified return value filtering logic
* @throws NullPointerException if either argument is null
* @throws IllegalArgumentException if the argument list of {@code filter}
* does not match the return type of target as described above
*/
public static
MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) {
MethodType targetType = target.type();
MethodType filterType = filter.type();
Class<?> rtype = targetType.returnType();
int filterValues = filterType.parameterCount();
if (filterValues == 0
? (rtype != void.class)
: (rtype != filterType.parameterType(0)))
throw newIllegalArgumentException("target and filter types do not match", target, filter);
// result = fold( lambda(retval, arg...) { filter(retval) },
// lambda( arg...) { target(arg...) } )
MethodType newType = targetType.changeReturnType(filterType.returnType());
MethodHandle result = null;
if (AdapterMethodHandle.canCollectArguments(filterType, targetType, 0, false)) {
result = AdapterMethodHandle.makeCollectArguments(filter, target, 0, false);
if (result != null) return result;
}
// FIXME: Too many nodes here.
assert(MethodHandleNatives.workaroundWithoutRicochetFrames()); // this class is deprecated
MethodHandle returner = dropArguments(filter, filterValues, targetType.parameterList());
result = foldArguments(returner, target);
assert(result.type().equals(newType));
return result;
}
/**
* Adapts a target method handle by pre-processing
* some of its arguments, and then calling the target with
* the result of the pre-processing, inserted into the original
* sequence of arguments.
* <p>
* The pre-processing is performed by {@code combiner}, a second method handle.
* Of the arguments passed to the adapter, the first {@code N} arguments
* are copied to the combiner, which is then called.
* (Here, {@code N} is defined as the parameter count of the combiner.)
* After this, control passes to the target, with any result
* from the combiner inserted before the original {@code N} incoming
* arguments.
* <p>
* If the combiner returns a value, the first parameter type of the target
* must be identical with the return type of the combiner, and the next
* {@code N} parameter types of the target must exactly match the parameters
* of the combiner.
* <p>
* If the combiner has a void return, no result will be inserted,
* and the first {@code N} parameter types of the target
* must exactly match the parameters of the combiner.
* <p>
* The resulting adapter is the same type as the target, except that the
* first parameter type is dropped,
* if it corresponds to the result of the combiner.
* <p>
* (Note that {@link #dropArguments(MethodHandle,int,List) dropArguments} can be used to remove any arguments
* that either the combiner or the target does not wish to receive.
* If some of the incoming arguments are destined only for the combiner,
* consider using {@link MethodHandle#asCollector asCollector} instead, since those
* arguments will not need to be live on the stack on entry to the
* target.)
* <b>Example:</b>
* <p><blockquote><pre>
import static java.lang.invoke.MethodHandles.*;
import static java.lang.invoke.MethodType.*;
...
MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
"println", methodType(void.class, String.class))
.bindTo(System.out);
MethodHandle cat = lookup().findVirtual(String.class,
"concat", methodType(String.class, String.class));
assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
MethodHandle catTrace = foldArguments(cat, trace);
// also prints "boo":
assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
* </pre></blockquote>
* <p> Here is pseudocode for the resulting adapter:
* <blockquote><pre>
* // there are N arguments in A...
* T target(V, A[N]..., B...);
* V combiner(A...);
* T adapter(A... a, B... b) {
* V v = combiner(a...);
* return target(v, a..., b...);
* }
* // and if the combiner has a void return:
* T target2(A[N]..., B...);
* void combiner2(A...);
* T adapter2(A... a, B... b) {
* combiner2(a...);
* return target2(a..., b...);
* }
* </pre></blockquote>
* @param target the method handle to invoke after arguments are combined
* @param combiner method handle to call initially on the incoming arguments
* @return method handle which incorporates the specified argument folding logic
* @throws NullPointerException if either argument is null
* @throws IllegalArgumentException if {@code combiner}'s return type
* is non-void and not the same as the first argument type of
* the target, or if the initial {@code N} argument types
* of the target
* (skipping one matching the {@code combiner}'s return type)
* are not identical with the argument types of {@code combiner}
*/
public static
MethodHandle foldArguments(MethodHandle target, MethodHandle combiner) {
int pos = 0;
MethodType targetType = target.type();
MethodType combinerType = combiner.type();
int foldPos = pos;
int foldArgs = combinerType.parameterCount();
int foldVals = combinerType.returnType() == void.class ? 0 : 1;
int afterInsertPos = foldPos + foldVals;
boolean ok = (targetType.parameterCount() >= afterInsertPos + foldArgs);
if (ok && !(combinerType.parameterList()
.equals(targetType.parameterList().subList(afterInsertPos,
afterInsertPos + foldArgs))))
ok = false;
if (ok && foldVals != 0 && !combinerType.returnType().equals(targetType.parameterType(0)))
ok = false;
if (!ok)
throw misMatchedTypes("target and combiner types", targetType, combinerType);
MethodType newType = targetType.dropParameterTypes(foldPos, afterInsertPos);
MethodHandle res = MethodHandleImpl.foldArguments(target, newType, foldPos, combiner);
if (res == null) throw newIllegalArgumentException("cannot fold from "+newType+" to " +targetType);
return res;
}
/**
* Makes a method handle which adapts a target method handle,
* by guarding it with a test, a boolean-valued method handle.
* If the guard fails, a fallback handle is called instead.
* All three method handles must have the same corresponding
* argument and return types, except that the return type
* of the test must be boolean, and the test is allowed
* to have fewer arguments than the other two method handles.
* <p> Here is pseudocode for the resulting adapter:
* <blockquote><pre>
* boolean test(A...);
* T target(A...,B...);
* T fallback(A...,B...);
* T adapter(A... a,B... b) {
* if (test(a...))
* return target(a..., b...);
* else
* return fallback(a..., b...);
* }
* </pre></blockquote>
* Note that the test arguments ({@code a...} in the pseudocode) cannot
* be modified by execution of the test, and so are passed unchanged
* from the caller to the target or fallback as appropriate.
* @param test method handle used for test, must return boolean
* @param target method handle to call if test passes
* @param fallback method handle to call if test fails
* @return method handle which incorporates the specified if/then/else logic
* @throws NullPointerException if any argument is null
* @throws IllegalArgumentException if {@code test} does not return boolean,
* or if all three method types do not match (with the return
* type of {@code test} changed to match that of the target).
*/
public static
MethodHandle guardWithTest(MethodHandle test,
MethodHandle target,
MethodHandle fallback) {
MethodType gtype = test.type();
MethodType ttype = target.type();
MethodType ftype = fallback.type();
if (!ttype.equals(ftype))
throw misMatchedTypes("target and fallback types", ttype, ftype);
if (gtype.returnType() != boolean.class)
throw newIllegalArgumentException("guard type is not a predicate "+gtype);
List<Class<?>> targs = ttype.parameterList();
List<Class<?>> gargs = gtype.parameterList();
if (!targs.equals(gargs)) {
int gpc = gargs.size(), tpc = targs.size();
if (gpc >= tpc || !targs.subList(0, gpc).equals(gargs))
throw misMatchedTypes("target and test types", ttype, gtype);
test = dropArguments(test, gpc, targs.subList(gpc, tpc));
gtype = test.type();
}
return MethodHandleImpl.makeGuardWithTest(test, target, fallback);
}
static RuntimeException misMatchedTypes(String what, MethodType t1, MethodType t2) {
return newIllegalArgumentException(what + " must match: " + t1 + " != " + t2);
}
/**
* Makes a method handle which adapts a target method handle,
* by running it inside an exception handler.
* If the target returns normally, the adapter returns that value.
* If an exception matching the specified type is thrown, the fallback
* handle is called instead on the exception, plus the original arguments.
* <p>
* The target and handler must have the same corresponding
* argument and return types, except that handler may omit trailing arguments
* (similarly to the predicate in {@link #guardWithTest guardWithTest}).
* Also, the handler must have an extra leading parameter of {@code exType} or a supertype.
* <p> Here is pseudocode for the resulting adapter:
* <blockquote><pre>
* T target(A..., B...);
* T handler(ExType, A...);
* T adapter(A... a, B... b) {
* try {
* return target(a..., b...);
* } catch (ExType ex) {
* return handler(ex, a...);
* }
* }
* </pre></blockquote>
* Note that the saved arguments ({@code a...} in the pseudocode) cannot
* be modified by execution of the target, and so are passed unchanged
* from the caller to the handler, if the handler is invoked.
* <p>
* The target and handler must return the same type, even if the handler
* always throws. (This might happen, for instance, because the handler
* is simulating a {@code finally} clause).
* To create such a throwing handler, compose the handler creation logic
* with {@link #throwException throwException},
* in order to create a method handle of the correct return type.
* @param target method handle to call
* @param exType the type of exception which the handler will catch
* @param handler method handle to call if a matching exception is thrown
* @return method handle which incorporates the specified try/catch logic
* @throws NullPointerException if any argument is null
* @throws IllegalArgumentException if {@code handler} does not accept
* the given exception type, or if the method handle types do
* not match in their return types and their
* corresponding parameters
*/
public static
MethodHandle catchException(MethodHandle target,
Class<? extends Throwable> exType,
MethodHandle handler) {
MethodType ttype = target.type();
MethodType htype = handler.type();
if (htype.parameterCount() < 1 ||
!htype.parameterType(0).isAssignableFrom(exType))
throw newIllegalArgumentException("handler does not accept exception type "+exType);
if (htype.returnType() != ttype.returnType())
throw misMatchedTypes("target and handler return types", ttype, htype);
List<Class<?>> targs = ttype.parameterList();
List<Class<?>> hargs = htype.parameterList();
hargs = hargs.subList(1, hargs.size()); // omit leading parameter from handler
if (!targs.equals(hargs)) {
int hpc = hargs.size(), tpc = targs.size();
if (hpc >= tpc || !targs.subList(0, hpc).equals(hargs))
throw misMatchedTypes("target and handler types", ttype, htype);
handler = dropArguments(handler, 1+hpc, targs.subList(hpc, tpc));
htype = handler.type();
}
return MethodHandleImpl.makeGuardWithCatch(target, exType, handler);
}
/**
* Produces a method handle which will throw exceptions of the given {@code exType}.
* The method handle will accept a single argument of {@code exType},
* and immediately throw it as an exception.
* The method type will nominally specify a return of {@code returnType}.
* The return type may be anything convenient: It doesn't matter to the
* method handle's behavior, since it will never return normally.
* @return method handle which can throw the given exceptions
* @throws NullPointerException if either argument is null
*/
public static
MethodHandle throwException(Class<?> returnType, Class<? extends Throwable> exType) {
return MethodHandleImpl.throwException(MethodType.methodType(returnType, exType));
}
}