/*
* Copyright (c) 2014, 2016, Oracle and/or its affiliates. All rights reserved.
* 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,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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package java.lang.reflect;
import java.lang.module.Configuration;
import java.lang.module.ModuleDescriptor;
import java.lang.module.ResolvedModule;
import java.util.ArrayDeque;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Deque;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Objects;
import java.util.Optional;
import java.util.Set;
import java.util.concurrent.CopyOnWriteArrayList;
import java.util.function.Function;
import java.util.stream.Collectors;
import java.util.stream.Stream;
import jdk.internal.loader.ClassLoaderValue;
import jdk.internal.loader.Loader;
import jdk.internal.loader.LoaderPool;
import jdk.internal.misc.SharedSecrets;
import jdk.internal.module.Modules;
import jdk.internal.module.ServicesCatalog;
import sun.security.util.SecurityConstants;
/**
* A layer of modules in the Java virtual machine.
*
* <p> A layer is created from a graph of modules that is the {@link
* Configuration} and a function that maps each module to a {@link ClassLoader}.
* Creating a layer informs the Java virtual machine about the classes that
* may be loaded from modules so that the Java virtual machine knows which
* module that each class is a member of. Each layer, except the {@link
* #empty() empty} layer, has at least one {@link #parents() parent}. </p>
*
* <p> Creating a layer creates a {@link Module} object for each {@link
* ResolvedModule} in the configuration. For each resolved module that is
* {@link ResolvedModule#reads() read}, the {@code Module} {@link
* Module#canRead reads} the corresponding run-time {@code Module}, which may
* be in the same layer or a parent layer. The {@code Module} {@link
* Module#isExported(String) exports} the packages described by its {@link
* ModuleDescriptor}. </p>
*
* <p> The {@link #defineModulesWithOneLoader defineModulesWithOneLoader} and
* {@link #defineModulesWithManyLoaders defineModulesWithManyLoaders} methods
* provide convenient ways to create a {@code Layer} where all modules are
* mapped to a single class loader or where each module is mapped to its own
* class loader. The {@link #defineModules defineModules} method is for more
* advanced cases where modules are mapped to custom class loaders by means of
* a function specified to the method. Each of these methods has an instance
* and static variant. The instance methods create a layer with the receiver
* as the parent layer. The static methods are for more advanced cases where
* there can be more than one parent layer or a {@link Layer.Controller
* Controller} is needed to control modules in the layer. </p>
*
* <p> A Java virtual machine has at least one non-empty layer, the {@link
* #boot() boot} layer, that is created when the Java virtual machine is
* started. The boot layer contains module {@code java.base} and is the only
* layer in the Java virtual machine with a module named "{@code java.base}".
* The modules in the boot layer are mapped to the bootstrap class loader and
* other class loaders that are <a href="../ClassLoader.html#builtinLoaders">
* built-in</a> into the Java virtual machine. The boot layer will often be
* the {@link #parents() parent} when creating additional layers. </p>
*
* <p> As when creating a {@code Configuration},
* {@link ModuleDescriptor#isAutomatic() automatic} modules receive
* <a href="../module/Configuration.html#automaticmoduleresolution">special
* treatment</a> when creating a layer. An automatic module is created in the
* Java virtual machine as a {@code Module} that reads every unnamed {@code
* Module} in the Java virtual machine. </p>
*
* <p> Unless otherwise specified, passing a {@code null} argument to a method
* in this class causes a {@link NullPointerException NullPointerException} to
* be thrown. </p>
*
* <h3> Example usage: </h3>
*
* <p> This example creates a configuration by resolving a module named
* "{@code myapp}" with the configuration for the boot layer as the parent. It
* then creates a new layer with the modules in this configuration. All modules
* are defined to the same class loader. </p>
*
* <pre>{@code
* ModuleFinder finder = ModuleFinder.of(dir1, dir2, dir3);
*
* Layer parent = Layer.boot();
*
* Configuration cf = parent.configuration()
* .resolveRequires(finder, ModuleFinder.of(), Set.of("myapp"));
*
* ClassLoader scl = ClassLoader.getSystemClassLoader();
*
* Layer layer = parent.defineModulesWithOneLoader(cf, scl);
*
* Class<?> c = layer.findLoader("myapp").loadClass("app.Main");
* }</pre>
*
* @since 9
* @see Module#getLayer()
*/
public final class Layer {
// the empty Layer
private static final Layer EMPTY_LAYER
= new Layer(Configuration.empty(), List.of(), null);
// the configuration from which this Layer was created
private final Configuration cf;
// parent layers, empty in the case of the empty layer
private final List<Layer> parents;
// maps module name to jlr.Module
private final Map<String, Module> nameToModule;
/**
* Creates a new Layer from the modules in the given configuration.
*/
private Layer(Configuration cf,
List<Layer> parents,
Function<String, ClassLoader> clf)
{
this.cf = cf;
this.parents = parents; // no need to do defensive copy
Map<String, Module> map;
if (parents.isEmpty()) {
map = Collections.emptyMap();
} else {
map = Module.defineModules(cf, clf, this);
}
this.nameToModule = map; // no need to do defensive copy
}
/**
* Controls a layer. The static methods defined by {@link Layer} to create
* module layers return a {@code Controller} that can be used to control
* modules in the layer.
*
* @apiNote Care should be taken with {@code Controller} objects, they
* should never be shared with untrusted code.
*
* @since 9
*/
public static final class Controller {
private final Layer layer;
Controller(Layer layer) {
this.layer = layer;
}
/**
* Returns the layer that this object controls.
*
* @return the layer
*/
public Layer layer() {
return layer;
}
private void ensureInLayer(Module source) {
if (!layer.modules().contains(source))
throw new IllegalArgumentException(source + " not in layer");
}
/**
* Updates module {@code source} in the layer to read module
* {@code target}. This method is a no-op if {@code source} already
* reads {@code target}.
*
* @implNote <em>Read edges</em> added by this method are <em>weak</em>
* and do not prevent {@code target} from being GC'ed when {@code source}
* is strongly reachable.
*
* @param source
* The source module
* @param target
* The target module to read
*
* @return This controller
*
* @throws IllegalArgumentException
* If {@code source} is not in the layer
*
* @see Module#addReads
*/
public Controller addReads(Module source, Module target) {
Objects.requireNonNull(source);
Objects.requireNonNull(target);
ensureInLayer(source);
Modules.addReads(source, target);
return this;
}
/**
* Updates module {@code source} in the layer to open a package to
* module {@code target}. This method is a no-op if {@code source}
* already opens the package to at least {@code target}.
*
* @param source
* The source module
* @param pn
* The package name
* @param target
* The target module to read
*
* @return This controller
*
* @throws IllegalArgumentException
* If {@code source} is not in the layer or the package is not
* in the source module
*
* @see Module#addOpens
*/
public Controller addOpens(Module source, String pn, Module target) {
Objects.requireNonNull(source);
Objects.requireNonNull(source);
Objects.requireNonNull(target);
ensureInLayer(source);
Modules.addOpens(source, pn, target);
return this;
}
}
/**
* Creates a new layer, with this layer as its parent, by defining the
* modules in the given {@code Configuration} to the Java virtual machine.
* This method creates one class loader and defines all modules to that
* class loader. The {@link ClassLoader#getParent() parent} of each class
* loader is the given parent class loader. This method works exactly as
* specified by the static {@link
* #defineModulesWithOneLoader(Configuration,List,ClassLoader)
* defineModulesWithOneLoader} method when invoked with this layer as the
* parent. In other words, if this layer is {@code thisLayer} then this
* method is equivalent to invoking:
* <pre> {@code
* Layer.defineModulesWithOneLoader(cf, List.of(thisLayer), parentLoader).layer();
* }</pre>
*
* @param cf
* The configuration for the layer
* @param parentLoader
* The parent class loader for the class loader created by this
* method; may be {@code null} for the bootstrap class loader
*
* @return The newly created layer
*
* @throws IllegalArgumentException
* If the parent of the given configuration is not the configuration
* for this layer
* @throws LayerInstantiationException
* If all modules cannot be defined to the same class loader for any
* of the reasons listed above or the layer cannot be created because
* the configuration contains a module named "{@code java.base}" or
* a module with a package name starting with "{@code java.}"
* @throws SecurityException
* If {@code RuntimePermission("createClassLoader")} or
* {@code RuntimePermission("getClassLoader")} is denied by
* the security manager
*
* @see #findLoader
*/
public Layer defineModulesWithOneLoader(Configuration cf,
ClassLoader parentLoader) {
return defineModulesWithOneLoader(cf, List.of(this), parentLoader).layer();
}
/**
* Creates a new layer, with this layer as its parent, by defining the
* modules in the given {@code Configuration} to the Java virtual machine.
* Each module is defined to its own {@link ClassLoader} created by this
* method. The {@link ClassLoader#getParent() parent} of each class loader
* is the given parent class loader. This method works exactly as specified
* by the static {@link
* #defineModulesWithManyLoaders(Configuration,List,ClassLoader)
* defineModulesWithManyLoaders} method when invoked with this layer as the
* parent. In other words, if this layer is {@code thisLayer} then this
* method is equivalent to invoking:
* <pre> {@code
* Layer.defineModulesWithManyLoaders(cf, List.of(thisLayer), parentLoader).layer();
* }</pre>
*
* @param cf
* The configuration for the layer
* @param parentLoader
* The parent class loader for each of the class loaders created by
* this method; may be {@code null} for the bootstrap class loader
*
* @return The newly created layer
*
* @throws IllegalArgumentException
* If the parent of the given configuration is not the configuration
* for this layer
* @throws LayerInstantiationException
* If the layer cannot be created because the configuration contains
* a module named "{@code java.base}" or a module with a package
* name starting with "{@code java.}"
* @throws SecurityException
* If {@code RuntimePermission("createClassLoader")} or
* {@code RuntimePermission("getClassLoader")} is denied by
* the security manager
*
* @see #findLoader
*/
public Layer defineModulesWithManyLoaders(Configuration cf,
ClassLoader parentLoader) {
return defineModulesWithManyLoaders(cf, List.of(this), parentLoader).layer();
}
/**
* Creates a new layer, with this layer as its parent, by defining the
* modules in the given {@code Configuration} to the Java virtual machine.
* Each module is mapped, by name, to its class loader by means of the
* given function. This method works exactly as specified by the static
* {@link #defineModules(Configuration,List,Function) defineModules}
* method when invoked with this layer as the parent. In other words, if
* this layer is {@code thisLayer} then this method is equivalent to
* invoking:
* <pre> {@code
* Layer.defineModules(cf, List.of(thisLayer), clf).layer();
* }</pre>
*
* @param cf
* The configuration for the layer
* @param clf
* The function to map a module name to a class loader
*
* @return The newly created layer
*
* @throws IllegalArgumentException
* If the parent of the given configuration is not the configuration
* for this layer
* @throws LayerInstantiationException
* If creating the {@code Layer} fails for any of the reasons
* listed above, the layer cannot be created because the
* configuration contains a module named "{@code java.base}",
* a module with a package name starting with "{@code java.}" is
* mapped to a class loader other than the {@link
* ClassLoader#getPlatformClassLoader() platform class loader},
* or the function to map a module name to a class loader returns
* {@code null}
* @throws SecurityException
* If {@code RuntimePermission("getClassLoader")} is denied by
* the security manager
*/
public Layer defineModules(Configuration cf,
Function<String, ClassLoader> clf) {
return defineModules(cf, List.of(this), clf).layer();
}
/**
* Creates a new layer by defining the modules in the given {@code
* Configuration} to the Java virtual machine. This method creates one
* class loader and defines all modules to that class loader.
*
* <p> The class loader created by this method implements <em>direct
* delegation</em> when loading types from modules. When its {@link
* ClassLoader#loadClass(String, boolean) loadClass} method is invoked to
* load a class then it uses the package name of the class to map it to a
* module. This may be a module in this layer and hence defined to the same
* class loader. It may be a package in a module in a parent layer that is
* exported to one or more of the modules in this layer. The class
* loader delegates to the class loader of the module, throwing {@code
* ClassNotFoundException} if not found by that class loader.
*
* When {@code loadClass} is invoked to load classes that do not map to a
* module then it delegates to the parent class loader. </p>
*
* <p> Attempting to create a layer with all modules defined to the same
* class loader can fail for the following reasons:
*
* <ul>
*
* <li><p> <em>Overlapping packages</em>: Two or more modules in the
* configuration have the same package. </p></li>
*
* <li><p> <em>Split delegation</em>: The resulting class loader would
* need to delegate to more than one class loader in order to load types
* in a specific package. </p></li>
*
* </ul>
*
* <p> If there is a security manager then the class loader created by
* this method will load classes and resources with privileges that are
* restricted by the calling context of this method. </p>
*
* @param cf
* The configuration for the layer
* @param parentLayers
* The list parent layers in search order
* @param parentLoader
* The parent class loader for the class loader created by this
* method; may be {@code null} for the bootstrap class loader
*
* @return A controller that controls the newly created layer
*
* @throws IllegalArgumentException
* If the parent configurations do not match the configuration of
* the parent layers, including order
* @throws LayerInstantiationException
* If all modules cannot be defined to the same class loader for any
* of the reasons listed above or the layer cannot be created because
* the configuration contains a module named "{@code java.base}" or
* a module with a package name starting with "{@code java.}"
* @throws SecurityException
* If {@code RuntimePermission("createClassLoader")} or
* {@code RuntimePermission("getClassLoader")} is denied by
* the security manager
*
* @see #findLoader
*/
public static Controller defineModulesWithOneLoader(Configuration cf,
List<Layer> parentLayers,
ClassLoader parentLoader)
{
List<Layer> parents = new ArrayList<>(parentLayers);
checkConfiguration(cf, parents);
checkCreateClassLoaderPermission();
checkGetClassLoaderPermission();
try {
Loader loader = new Loader(cf.modules(), parentLoader);
loader.initRemotePackageMap(cf, parents);
Layer layer = new Layer(cf, parents, mn -> loader);
return new Controller(layer);
} catch (IllegalArgumentException e) {
throw new LayerInstantiationException(e.getMessage());
}
}
/**
* Creates a new layer by defining the modules in the given {@code
* Configuration} to the Java virtual machine. Each module is defined to
* its own {@link ClassLoader} created by this method. The {@link
* ClassLoader#getParent() parent} of each class loader is the given parent
* class loader.
*
* <p> The class loaders created by this method implement <em>direct
* delegation</em> when loading types from modules. When {@link
* ClassLoader#loadClass(String, boolean) loadClass} method is invoked to
* load a class then it uses the package name of the class to map it to a
* module. The package may be in the module defined to the class loader.
* The package may be exported by another module in this layer to the
* module defined to the class loader. It may be in a package exported by a
* module in a parent layer. The class loader delegates to the class loader
* of the module, throwing {@code ClassNotFoundException} if not found by
* that class loader.
*
* When {@code loadClass} is invoked to load classes that do not map to a
* module then it delegates to the parent class loader. </p>
*
* <p> If there is a security manager then the class loaders created by
* this method will load classes and resources with privileges that are
* restricted by the calling context of this method. </p>
*
* @param cf
* The configuration for the layer
* @param parentLayers
* The list parent layers in search order
* @param parentLoader
* The parent class loader for each of the class loaders created by
* this method; may be {@code null} for the bootstrap class loader
*
* @return A controller that controls the newly created layer
*
* @throws IllegalArgumentException
* If the parent configurations do not match the configuration of
* the parent layers, including order
* @throws LayerInstantiationException
* If the layer cannot be created because the configuration contains
* a module named "{@code java.base}" or a module with a package
* name starting with "{@code java.}"
* @throws SecurityException
* If {@code RuntimePermission("createClassLoader")} or
* {@code RuntimePermission("getClassLoader")} is denied by
* the security manager
*
* @see #findLoader
*/
public static Controller defineModulesWithManyLoaders(Configuration cf,
List<Layer> parentLayers,
ClassLoader parentLoader)
{
List<Layer> parents = new ArrayList<>(parentLayers);
checkConfiguration(cf, parents);
checkCreateClassLoaderPermission();
checkGetClassLoaderPermission();
LoaderPool pool = new LoaderPool(cf, parents, parentLoader);
try {
Layer layer = new Layer(cf, parents, pool::loaderFor);
return new Controller(layer);
} catch (IllegalArgumentException e) {
throw new LayerInstantiationException(e.getMessage());
}
}
/**
* Creates a new layer by defining the modules in the given {@code
* Configuration} to the Java virtual machine.
* Each module is mapped, by name, to its class loader by means of the
* given function. The class loader delegation implemented by these class
* loaders must respect module readability. The class loaders should be
* {@link ClassLoader#registerAsParallelCapable parallel-capable} so as to
* avoid deadlocks during class loading. In addition, the entity creating
* a new layer with this method should arrange that the class loaders are
* ready to load from these module before there are any attempts to load
* classes or resources.
*
* <p> Creating a {@code Layer} can fail for the following reasons: </p>
*
* <ul>
*
* <li><p> Two or more modules with the same package are mapped to the
* same class loader. </p></li>
*
* <li><p> A module is mapped to a class loader that already has a
* module of the same name defined to it. </p></li>
*
* <li><p> A module is mapped to a class loader that has already
* defined types in any of the packages in the module. </p></li>
*
* </ul>
*
* <p> If the function to map a module name to class loader throws an error
* or runtime exception then it is propagated to the caller of this method.
* </p>
*
* @apiNote It is implementation specific as to whether creating a Layer
* with this method is an atomic operation or not. Consequentially it is
* possible for this method to fail with some modules, but not all, defined
* to Java virtual machine.
*
* @param cf
* The configuration for the layer
* @param parentLayers
* The list parent layers in search order
* @param clf
* The function to map a module name to a class loader
*
* @return A controller that controls the newly created layer
*
* @throws IllegalArgumentException
* If the parent configurations do not match the configuration of
* the parent layers, including order
* @throws LayerInstantiationException
* If creating the {@code Layer} fails for any of the reasons
* listed above, the layer cannot be created because the
* configuration contains a module named "{@code java.base}",
* a module with a package name starting with "{@code java.}" is
* mapped to a class loader other than the {@link
* ClassLoader#getPlatformClassLoader() platform class loader},
* or the function to map a module name to a class loader returns
* {@code null}
* @throws SecurityException
* If {@code RuntimePermission("getClassLoader")} is denied by
* the security manager
*/
public static Controller defineModules(Configuration cf,
List<Layer> parentLayers,
Function<String, ClassLoader> clf)
{
List<Layer> parents = new ArrayList<>(parentLayers);
checkConfiguration(cf, parents);
Objects.requireNonNull(clf);
checkGetClassLoaderPermission();
// For now, no two modules in the boot Layer may contain the same
// package so we use a simple check for the boot Layer to keep
// the overhead at startup to a minimum
if (boot() == null) {
checkBootModulesForDuplicatePkgs(cf);
} else {
checkForDuplicatePkgs(cf, clf);
}
try {
Layer layer = new Layer(cf, parents, clf);
return new Controller(layer);
} catch (IllegalArgumentException iae) {
// IAE is thrown by VM when defining the module fails
throw new LayerInstantiationException(iae.getMessage());
}
}
/**
* Checks that the parent configurations match the configuration of
* the parent layers.
*/
private static void checkConfiguration(Configuration cf,
List<Layer> parentLayers)
{
Objects.requireNonNull(cf);
List<Configuration> parentConfigurations = cf.parents();
if (parentLayers.size() != parentConfigurations.size())
throw new IllegalArgumentException("wrong number of parents");
int index = 0;
for (Layer parent : parentLayers) {
if (parent.configuration() != parentConfigurations.get(index)) {
throw new IllegalArgumentException(
"Parent of configuration != configuration of this Layer");
}
index++;
}
}
private static void checkCreateClassLoaderPermission() {
SecurityManager sm = System.getSecurityManager();
if (sm != null)
sm.checkPermission(SecurityConstants.CREATE_CLASSLOADER_PERMISSION);
}
private static void checkGetClassLoaderPermission() {
SecurityManager sm = System.getSecurityManager();
if (sm != null)
sm.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
}
/**
* Checks a configuration for the boot Layer to ensure that no two modules
* have the same package.
*
* @throws LayerInstantiationException
*/
private static void checkBootModulesForDuplicatePkgs(Configuration cf) {
Map<String, String> packageToModule = new HashMap<>();
for (ResolvedModule resolvedModule : cf.modules()) {
ModuleDescriptor descriptor = resolvedModule.reference().descriptor();
String name = descriptor.name();
for (String p : descriptor.packages()) {
String other = packageToModule.putIfAbsent(p, name);
if (other != null) {
throw fail("Package " + p + " in both module "
+ name + " and module " + other);
}
}
}
}
/**
* Checks a configuration and the module-to-loader mapping to ensure that
* no two modules mapped to the same class loader have the same package.
* It also checks that no two automatic modules have the same package.
*
* @throws LayerInstantiationException
*/
private static void checkForDuplicatePkgs(Configuration cf,
Function<String, ClassLoader> clf)
{
// HashMap allows null keys
Map<ClassLoader, Set<String>> loaderToPackages = new HashMap<>();
for (ResolvedModule resolvedModule : cf.modules()) {
ModuleDescriptor descriptor = resolvedModule.reference().descriptor();
ClassLoader loader = clf.apply(descriptor.name());
Set<String> loaderPackages
= loaderToPackages.computeIfAbsent(loader, k -> new HashSet<>());
for (String pkg : descriptor.packages()) {
boolean added = loaderPackages.add(pkg);
if (!added) {
throw fail("More than one module with package %s mapped" +
" to the same class loader", pkg);
}
}
}
}
/**
* Creates a LayerInstantiationException with the a message formatted from
* the given format string and arguments.
*/
private static LayerInstantiationException fail(String fmt, Object ... args) {
String msg = String.format(fmt, args);
return new LayerInstantiationException(msg);
}
/**
* Returns the configuration for this layer.
*
* @return The configuration for this layer
*/
public Configuration configuration() {
return cf;
}
/**
* Returns the list of this layer's parents unless this is the
* {@linkplain #empty empty layer}, which has no parents and so an
* empty list is returned.
*
* @return The list of this layer's parents
*/
public List<Layer> parents() {
return parents;
}
/**
* Returns an ordered stream of layers. The first element is is this layer,
* the remaining elements are the parent layers in DFS order.
*
* @implNote For now, the assumption is that the number of elements will
* be very low and so this method does not use a specialized spliterator.
*/
Stream<Layer> layers() {
List<Layer> allLayers = this.allLayers;
if (allLayers != null)
return allLayers.stream();
allLayers = new ArrayList<>();
Set<Layer> visited = new HashSet<>();
Deque<Layer> stack = new ArrayDeque<>();
visited.add(this);
stack.push(this);
while (!stack.isEmpty()) {
Layer layer = stack.pop();
allLayers.add(layer);
// push in reverse order
for (int i = layer.parents.size() - 1; i >= 0; i--) {
Layer parent = layer.parents.get(i);
if (!visited.contains(parent)) {
visited.add(parent);
stack.push(parent);
}
}
}
this.allLayers = allLayers = Collections.unmodifiableList(allLayers);
return allLayers.stream();
}
private volatile List<Layer> allLayers;
/**
* Returns the set of the modules in this layer.
*
* @return A possibly-empty unmodifiable set of the modules in this layer
*/
public Set<Module> modules() {
return Collections.unmodifiableSet(
nameToModule.values().stream().collect(Collectors.toSet()));
}
/**
* Returns the module with the given name in this layer, or if not in this
* layer, the {@linkplain #parents parents} layers. Finding a module in
* parent layers is equivalent to invoking {@code findModule} on each
* parent, in search order, until the module is found or all parents have
* been searched. In a <em>tree of layers</em> then this is equivalent to
* a depth-first search.
*
* @param name
* The name of the module to find
*
* @return The module with the given name or an empty {@code Optional}
* if there isn't a module with this name in this layer or any
* parent layer
*/
public Optional<Module> findModule(String name) {
Objects.requireNonNull(name);
Module m = nameToModule.get(name);
if (m != null)
return Optional.of(m);
return layers()
.skip(1) // skip this layer
.map(l -> l.nameToModule)
.filter(map -> map.containsKey(name))
.map(map -> map.get(name))
.findAny();
}
/**
* Returns the {@code ClassLoader} for the module with the given name. If
* a module of the given name is not in this layer then the {@link #parents
* parent} layers are searched in the manner specified by {@link
* #findModule(String) findModule}.
*
* <p> If there is a security manager then its {@code checkPermission}
* method is called with a {@code RuntimePermission("getClassLoader")}
* permission to check that the caller is allowed to get access to the
* class loader. </p>
*
* @apiNote This method does not return an {@code Optional<ClassLoader>}
* because `null` must be used to represent the bootstrap class loader.
*
* @param name
* The name of the module to find
*
* @return The ClassLoader that the module is defined to
*
* @throws IllegalArgumentException if a module of the given name is not
* defined in this layer or any parent of this layer
*
* @throws SecurityException if denied by the security manager
*/
public ClassLoader findLoader(String name) {
Optional<Module> om = findModule(name);
// can't use map(Module::getClassLoader) as class loader can be null
if (om.isPresent()) {
return om.get().getClassLoader();
} else {
throw new IllegalArgumentException("Module " + name
+ " not known to this layer");
}
}
/**
* Returns a string describing this layer.
*
* @return A possibly empty string describing this layer
*/
@Override
public String toString() {
return modules().stream()
.map(Module::getName)
.collect(Collectors.joining(", "));
}
/**
* Returns the <em>empty</em> layer. There are no modules in the empty
* layer. It has no parents.
*
* @return The empty layer
*/
public static Layer empty() {
return EMPTY_LAYER;
}
/**
* Returns the boot layer. The boot layer contains at least one module,
* {@code java.base}. Its parent is the {@link #empty() empty} layer.
*
* @apiNote This method returns {@code null} during startup and before
* the boot layer is fully initialized.
*
* @return The boot layer
*/
public static Layer boot() {
return SharedSecrets.getJavaLangAccess().getBootLayer();
}
/**
* Returns the ServicesCatalog for this Layer, creating it if not
* already created.
*/
ServicesCatalog getServicesCatalog() {
ServicesCatalog servicesCatalog = this.servicesCatalog;
if (servicesCatalog != null)
return servicesCatalog;
synchronized (this) {
servicesCatalog = this.servicesCatalog;
if (servicesCatalog == null) {
servicesCatalog = ServicesCatalog.create();
nameToModule.values().forEach(servicesCatalog::register);
this.servicesCatalog = servicesCatalog;
}
}
return servicesCatalog;
}
private volatile ServicesCatalog servicesCatalog;
/**
* Record that this layer has at least one module defined to the given
* class loader.
*/
void bindToLoader(ClassLoader loader) {
// CLV.computeIfAbsent(loader, (cl, clv) -> new CopyOnWriteArrayList<>())
List<Layer> list = CLV.get(loader);
if (list == null) {
list = new CopyOnWriteArrayList<>();
List<Layer> previous = CLV.putIfAbsent(loader, list);
if (previous != null) list = previous;
}
list.add(this);
}
/**
* Returns a stream of the layers that have at least one module defined to
* the given class loader.
*/
static Stream<Layer> layers(ClassLoader loader) {
List<Layer> list = CLV.get(loader);
if (list != null) {
return list.stream();
} else {
return Stream.empty();
}
}
// the list of layers with modules defined to a class loader
private static final ClassLoaderValue<List<Layer>> CLV = new ClassLoaderValue<>();
}