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*
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* - Redistributions in binary form must reproduce the above copyright
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* - Neither the name of Oracle nor the names of its
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*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
* IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
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import java.lang.invoke.MethodHandle;
import java.lang.invoke.MethodHandles;
import java.lang.invoke.MethodType;
import java.util.ArrayList;
import java.util.List;
import jdk.dynalink.CallSiteDescriptor;
import jdk.dynalink.NamedOperation;
import jdk.dynalink.NamespaceOperation;
import jdk.dynalink.Operation;
import jdk.dynalink.StandardNamespace;
import jdk.dynalink.StandardOperation;
import jdk.dynalink.beans.BeansLinker;
import jdk.dynalink.linker.GuardedInvocation;
import jdk.dynalink.linker.GuardingDynamicLinker;
import jdk.dynalink.linker.GuardingDynamicLinkerExporter;
import jdk.dynalink.linker.LinkRequest;
import jdk.dynalink.linker.LinkerServices;
import jdk.dynalink.linker.TypeBasedGuardingDynamicLinker;
import jdk.dynalink.linker.support.Guards;
import jdk.dynalink.linker.support.Lookup;
/**
* This is a dynalink pluggable linker (see http://openjdk.java.net/jeps/276).
* This linker routes missing methods to Smalltalk-style doesNotUnderstand method.
* Object of any Java class that implements MissingMethodHandler is handled by this linker.
* For any method call, if a matching Java method is found, it is called. If there is no
* method by that name, then MissingMethodHandler.doesNotUnderstand is called.
*/
public final class MissingMethodLinkerExporter extends GuardingDynamicLinkerExporter {
static {
System.out.println("pluggable dynalink missing method linker loaded");
}
// represents a MissingMethod - just stores as name and also serves a guard type
public static class MissingMethod {
private final String name;
public MissingMethod(final String name) {
this.name = name;
}
public String getName() {
return name;
}
}
// MissingMethodHandler.doesNotUnderstand method
private static final MethodHandle DOES_NOT_UNDERSTAND;
// type of MissingMethodHandler - but "this" and String args are flipped
private static final MethodType FLIPPED_DOES_NOT_UNDERSTAND_TYPE;
// "is this a MissingMethod?" guard
private static final MethodHandle IS_MISSING_METHOD;
// MissingMethod object->it's name filter
private static final MethodHandle MISSING_METHOD_TO_NAME;
static {
DOES_NOT_UNDERSTAND = Lookup.PUBLIC.findVirtual(
MissingMethodHandler.class,
"doesNotUnderstand",
MethodType.methodType(Object.class, String.class, Object[].class));
FLIPPED_DOES_NOT_UNDERSTAND_TYPE =
MethodType.methodType(Object.class, String.class, MissingMethodHandler.class, Object[].class);
IS_MISSING_METHOD = Guards.isOfClass(MissingMethod.class,
MethodType.methodType(Boolean.TYPE, Object.class));
MISSING_METHOD_TO_NAME = Lookup.PUBLIC.findVirtual(MissingMethod.class,
"getName", MethodType.methodType(String.class));
}
@Override
public List<GuardingDynamicLinker> get() {
final ArrayList<GuardingDynamicLinker> linkers = new ArrayList<>();
final BeansLinker beansLinker = new BeansLinker();
linkers.add(new TypeBasedGuardingDynamicLinker() {
// only handles MissingMethodHandler and MissingMethod objects
@Override
public boolean canLinkType(final Class<?> type) {
return
MissingMethodHandler.class.isAssignableFrom(type) ||
type == MissingMethod.class;
}
@Override
public GuardedInvocation getGuardedInvocation(final LinkRequest request,
final LinkerServices linkerServices) throws Exception {
final Object self = request.getReceiver();
final CallSiteDescriptor desc = request.getCallSiteDescriptor();
// any method call is done by two steps. Step (1) GET_METHOD and (2) is CALL
// For step (1), we check if GET_METHOD can succeed by Java linker, if so
// we return that method object. If not, we return a MissingMethod object.
if (self instanceof MissingMethodHandler) {
// Check if this is a named GET_METHOD first.
final Operation namedOp = desc.getOperation();
final Operation namespaceOp = NamedOperation.getBaseOperation(namedOp);
final Operation op = NamespaceOperation.getBaseOperation(namespaceOp);
final boolean isGetMethod = op == StandardOperation.GET && StandardNamespace.findFirst(namespaceOp) == StandardNamespace.METHOD;
final Object name = NamedOperation.getName(namedOp);
if (isGetMethod && name instanceof String) {
final GuardingDynamicLinker javaLinker = beansLinker.getLinkerForClass(self.getClass());
GuardedInvocation inv;
try {
inv = javaLinker.getGuardedInvocation(request, linkerServices);
} catch (final Throwable th) {
inv = null;
}
final String nameStr = name.toString();
if (inv == null) {
// use "this" for just guard and drop it -- return a constant Method handle
// that returns a newly created MissingMethod object
final MethodHandle mh = MethodHandles.constant(Object.class, new MissingMethod(nameStr));
inv = new GuardedInvocation(
MethodHandles.dropArguments(mh, 0, Object.class),
Guards.isOfClass(self.getClass(), MethodType.methodType(Boolean.TYPE, Object.class)));
}
return inv;
}
} else if (self instanceof MissingMethod) {
// This is step (2). We call MissingMethodHandler.doesNotUnderstand here
// Check if this is this a CALL first.
final boolean isCall = NamedOperation.getBaseOperation(desc.getOperation()) == StandardOperation.CALL;
if (isCall) {
MethodHandle mh = DOES_NOT_UNDERSTAND;
// flip "this" and method name (String)
mh = MethodHandles.permuteArguments(mh, FLIPPED_DOES_NOT_UNDERSTAND_TYPE, 1, 0, 2);
// collect rest of the arguments as vararg
mh = mh.asCollector(Object[].class, desc.getMethodType().parameterCount() - 2);
// convert MissingMethod object to it's name
mh = MethodHandles.filterArguments(mh, 0, MISSING_METHOD_TO_NAME);
return new GuardedInvocation(mh, IS_MISSING_METHOD);
}
}
return null;
}
});
return linkers;
}
}