Quelle Module.java Sprache: JAVA

/*
* Copyright (c) 2014, 2022, 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;

import java.io.IOException;
import java.io.InputStream;
import java.lang.annotation.Annotation;
import java.lang.module.Configuration;
import java.lang.module.ModuleReference;
import java.lang.module.ModuleDescriptor;
import java.lang.module.ModuleDescriptor.Exports;
import java.lang.module.ModuleDescriptor.Opens;
import java.lang.module.ModuleDescriptor.Version;
import java.lang.module.ResolvedModule;
import java.lang.reflect.AnnotatedElement;
import java.net.URI;
import java.net.URL;
import java.security.AccessController;
import java.security.PrivilegedAction;
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.ConcurrentHashMap;
import java.util.function.Function;
import java.util.stream.Collectors;
import java.util.stream.Stream;

import jdk.internal.javac.PreviewFeature;
import jdk.internal.loader.BuiltinClassLoader;
import jdk.internal.loader.BootLoader;
import jdk.internal.loader.ClassLoaders;
import jdk.internal.misc.CDS;
import jdk.internal.module.ModuleBootstrap;
import jdk.internal.module.ModuleLoaderMap;
import jdk.internal.module.ServicesCatalog;
import jdk.internal.module.Resources;
import jdk.internal.org.objectweb.asm.AnnotationVisitor;
import jdk.internal.org.objectweb.asm.Attribute;
import jdk.internal.org.objectweb.asm.ClassReader;
import jdk.internal.org.objectweb.asm.ClassVisitor;
import jdk.internal.org.objectweb.asm.ClassWriter;
import jdk.internal.org.objectweb.asm.ModuleVisitor;
import jdk.internal.org.objectweb.asm.Opcodes;
import jdk.internal.reflect.CallerSensitive;
import jdk.internal.reflect.Reflection;
import jdk.internal.vm.annotation.Stable;
import sun.security.util.SecurityConstants;

/**
* Represents a run-time module, either {@link #isNamed() named} or unnamed.
*
* Named modules have a {@link #getName() name} and are constructed by the
* Java Virtual Machine when a graph of modules is defined to the Java virtual
* machine to create a {@linkplain ModuleLayer module layer}. 
*
* An unnamed module does not have a name. There is an unnamed module for
* each {@link ClassLoader ClassLoader}, obtained by invoking its {@link
* ClassLoader#getUnnamedModule() getUnnamedModule} method. All types that are
* not in a named module are members of their defining class loader's unnamed
* module. 
*
* The package names that are parameters or returned by methods defined in
* this class are the fully-qualified names of the packages as defined in
* section {@jls 6.5.3} of <cite>The Java Language Specification</cite>, for
* example, {@code "java.lang"}. 
*
* Unless otherwise specified, passing a {@code null} argument to a method
* in this class causes a {@link NullPointerException NullPointerException} to
* be thrown. 
*
* @since 9
* @see Class#getModule()
* @jls 7.7 Module Declarations
*/

public final class Module implements AnnotatedElement {

 // the layer that contains this module, can be null
 private final ModuleLayer layer;

 // module name and loader, these fields are read by VM
 private final String name;
 private final ClassLoader loader;

 // the module descriptor
 private final ModuleDescriptor descriptor;

 // true, if this module allows restricted native access
 @Stable
 private boolean enableNativeAccess;

 /**
 * Creates a new named Module. The resulting Module will be defined to the
 * VM but will not read any other modules, will not have any exports setup
 * and will not be registered in the service catalog.
 */
 Module(ModuleLayer layer,
 ClassLoader loader,
 ModuleDescriptor descriptor,
 URI uri)
 {
 this.layer = layer;
 this.name = descriptor.name();
 this.loader = loader;
 this.descriptor = descriptor;

 // define module to VM

 boolean isOpen = descriptor.isOpen() || descriptor.isAutomatic();
 Version version = descriptor.version().orElse(null);
 String vs = Objects.toString(version, null);
 String loc = Objects.toString(uri, null);
 Object[] packages = descriptor.packages().toArray();
 defineModule0(this, isOpen, vs, loc, packages);
 if (loader == null || loader == ClassLoaders.platformClassLoader()) {
 // boot/builtin modules are always native
 implAddEnableNativeAccess();
 }
 }

 /**
 * Create the unnamed Module for the given ClassLoader.
 *
 * @see ClassLoader#getUnnamedModule
 */
 Module(ClassLoader loader) {
 this.layer = null;
 this.name = null;
 this.loader = loader;
 this.descriptor = null;
 }

 /**
 * Creates a named module but without defining the module to the VM.
 *
 * @apiNote This constructor is for VM white-box testing.
 */
 Module(ClassLoader loader, ModuleDescriptor descriptor) {
 this.layer = null;
 this.name = descriptor.name();
 this.loader = loader;
 this.descriptor = descriptor;
 }

 /**
 * Returns {@code true} if this module is a named module.
 *
 * @return {@code true} if this is a named module
 *
 * @see ClassLoader#getUnnamedModule()
 * @jls 7.7.5 Unnamed Modules
 */
 public boolean isNamed() {
 return name != null;
 }

 /**
 * Returns the module name or {@code null} if this module is an unnamed
 * module.
 *
 * @return The module name
 */
 public String getName() {
 return name;
 }

 /**
 * Returns the {@code ClassLoader} for this module.
 *
 * If there is a security manager then its {@code checkPermission}
 * method if first called with a {@code RuntimePermission("getClassLoader")}
 * permission to check that the caller is allowed to get access to the
 * class loader. 
 *
 * @return The class loader for this module
 *
 * @throws SecurityException
 * If denied by the security manager
 */
 public ClassLoader getClassLoader() {
 @SuppressWarnings("removal")
 SecurityManager sm = System.getSecurityManager();
 if (sm != null) {
 sm.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
 }
 return loader;
 }

 /**
 * Returns the module descriptor for this module or {@code null} if this
 * module is an unnamed module.
 *
 * @return The module descriptor for this module
 */
 public ModuleDescriptor getDescriptor() {
 return descriptor;
 }

 /**
 * Returns the module layer that contains this module or {@code null} if
 * this module is not in a module layer.
 *
 * A module layer contains named modules and therefore this method always
 * returns {@code null} when invoked on an unnamed module.
 *
 * <a href="reflect/Proxy.html#dynamicmodule">Dynamic modules</a> are
 * named modules that are generated at runtime. A dynamic module may or may
 * not be in a module layer. 
 *
 * @return The module layer that contains this module
 *
 * @see java.lang.reflect.Proxy
 */
 public ModuleLayer getLayer() {
 if (isNamed()) {
 ModuleLayer layer = this.layer;
 if (layer != null)
 return layer;

 // special-case java.base as it is created before the boot layer
 if (loader == null && name.equals("java.base")) {
 return ModuleLayer.boot();
 }
 }
 return null;
 }

 /**
 * Update this module to allow access to restricted methods.
 */
 synchronized Module implAddEnableNativeAccess() {
 enableNativeAccess = true;
 return this;
 }

 /**
 * Returns {@code true} if this module can access
 * <a href="foreign/package-summary.html#restricted">restricted</a> methods.
 *
 * @since 20
 *
 * @return {@code true} if this module can access restricted methods.
 */
 @PreviewFeature(feature=PreviewFeature.Feature.FOREIGN)
 public boolean isNativeAccessEnabled() {
 Module target = moduleForNativeAccess();
 synchronized(target) {
 return target.enableNativeAccess;
 }
 }

 // Returns the Module object that holds the enableNativeAccess
 // flag for this module.
 private Module moduleForNativeAccess() {
 return isNamed() ? this : ALL_UNNAMED_MODULE;
 }

 // This is invoked from Reflection.ensureNativeAccess
 void ensureNativeAccess(Class<?> owner, String methodName) {
 // The target module whose enableNativeAccess flag is ensured
 Module target = moduleForNativeAccess();
 // racy read of the enable native access flag
 boolean isNativeAccessEnabled = target.enableNativeAccess;
 if (!isNativeAccessEnabled) {
 synchronized (target) {
 // safe read of the enableNativeAccess of the target module
 isNativeAccessEnabled = target.enableNativeAccess;

 // check again with the safely read flag
 if (isNativeAccessEnabled) {
 // another thread beat us to it - nothing to do
 return;
 } else if (ModuleBootstrap.hasEnableNativeAccessFlag()) {
 throw new IllegalCallerException("Illegal native access from: " + this);
 } else {
 // warn and set flag, so that only one warning is reported per module
 String cls = owner.getName();
 String mtd = cls + "::" + methodName;
 String mod = isNamed() ? "module " + getName() : "the unnamed module";
 String modflag = isNamed() ? getName() : "ALL-UNNAMED";
 System.err.printf("""
 WARNING: A restricted method in %s has been called
 WARNING: %s has been called by %s
 WARNING: Use --enable-native-access=%s to avoid a warning for this module
 %n""", cls, mtd, mod, modflag);

 // set the flag
 target.enableNativeAccess = true;
 }
 }
 }
 }

 /**
 * Update all unnamed modules to allow access to restricted methods.
 */
 static void implAddEnableNativeAccessToAllUnnamed() {
 synchronized (ALL_UNNAMED_MODULE) {
 ALL_UNNAMED_MODULE.enableNativeAccess = true;
 }
 }

 // --

 // special Module to mean "all unnamed modules"
 private static final Module ALL_UNNAMED_MODULE;
 private static final Set<Module> ALL_UNNAMED_MODULE_SET;

 // special Module to mean "everyone"
 private static final Module EVERYONE_MODULE;
 private static final Set<Module> EVERYONE_SET;

 private static class ArchivedData {
 private static ArchivedData archivedData;
 private final Module allUnnamedModule;
 private final Set<Module> allUnnamedModules;
 private final Module everyoneModule;
 private final Set<Module> everyoneSet;

 private ArchivedData() {
 this.allUnnamedModule = ALL_UNNAMED_MODULE;
 this.allUnnamedModules = ALL_UNNAMED_MODULE_SET;
 this.everyoneModule = EVERYONE_MODULE;
 this.everyoneSet = EVERYONE_SET;
 }

 static void archive() {
 archivedData = new ArchivedData();
 }

 static ArchivedData get() {
 return archivedData;
 }

 static {
 CDS.initializeFromArchive(ArchivedData.class);
 }
 }

 static {
 ArchivedData archivedData = ArchivedData.get();
 if (archivedData != null) {
 ALL_UNNAMED_MODULE = archivedData.allUnnamedModule;
 ALL_UNNAMED_MODULE_SET = archivedData.allUnnamedModules;
 EVERYONE_MODULE = archivedData.everyoneModule;
 EVERYONE_SET = archivedData.everyoneSet;
 } else {
 ALL_UNNAMED_MODULE = new Module(null);
 ALL_UNNAMED_MODULE_SET = Set.of(ALL_UNNAMED_MODULE);
 EVERYONE_MODULE = new Module(null);
 EVERYONE_SET = Set.of(EVERYONE_MODULE);
 ArchivedData.archive();
 }
 }

 /**
 * The holder of data structures to support readability, exports, and
 * service use added at runtime with the reflective APIs.
 */
 private static class ReflectionData {
 /**
 * A module (1st key) reads another module (2nd key)
 */
 static final WeakPairMap<Module, Module, Boolean> reads =
 new WeakPairMap<>();

 /**
 * A module (1st key) exports or opens a package to another module
 * (2nd key). The map value is a map of package name to a boolean
 * that indicates if the package is opened.
 */
 static final WeakPairMap<Module, Module, Map<String, Boolean>> exports =
 new WeakPairMap<>();

 /**
 * A module (1st key) uses a service (2nd key)
 */
 static final WeakPairMap<Module, Class<?>, Boolean> uses =
 new WeakPairMap<>();
 }

 // -- readability --

 // the modules that this module reads
 private volatile Set<Module> reads;

 /**
 * Indicates if this module reads the given module. This method returns
 * {@code true} if invoked to test if this module reads itself. It also
 * returns {@code true} if invoked on an unnamed module (as unnamed
 * modules read all modules).
 *
 * @param other
 * The other module
 *
 * @return {@code true} if this module reads {@code other}
 *
 * @see #addReads(Module)
 */
 public boolean canRead(Module other) {
 Objects.requireNonNull(other);

 // an unnamed module reads all modules
 if (!this.isNamed())
 return true;

 // all modules read themselves
 if (other == this)
 return true;

 // check if this module reads other
 if (other.isNamed()) {
 Set<Module> reads = this.reads; // volatile read
 if (reads != null && reads.contains(other))
 return true;
 }

 // check if this module reads the other module reflectively
 if (ReflectionData.reads.containsKeyPair(this, other))
 return true;

 // if other is an unnamed module then check if this module reads
 // all unnamed modules
 if (!other.isNamed()
 && ReflectionData.reads.containsKeyPair(this, ALL_UNNAMED_MODULE))
 return true;

 return false;
 }

 /**
 * If the caller's module is this module then update this module to read
 * the given module.
 *
 * This method is a no-op if {@code other} is this module (all modules read
 * themselves), this module is an unnamed module (as unnamed modules read
 * all modules), or this module already reads {@code other}.
 *
 * @implNote Read edges added by this method are weak and
 * do not prevent {@code other} from being GC'ed when this module is
 * strongly reachable.
 *
 * @param other
 * The other module
 *
 * @return this module
 *
 * @throws IllegalCallerException
 * If this is a named module and the caller's module is not this
 * module
 *
 * @see #canRead
 */
 @CallerSensitive
 public Module addReads(Module other) {
 Objects.requireNonNull(other);
 if (this.isNamed()) {
 Module caller = getCallerModule(Reflection.getCallerClass());
 if (caller != this) {
 throw new IllegalCallerException(caller + " != " + this);
 }
 implAddReads(other, true);
 }
 return this;
 }

 /**
 * Updates this module to read another module.
 *
 * @apiNote Used by the --add-reads command line option.
 */
 void implAddReads(Module other) {
 implAddReads(other, true);
 }

 /**
 * Updates this module to read all unnamed modules.
 *
 * @apiNote Used by the --add-reads command line option.
 */
 void implAddReadsAllUnnamed() {
 implAddReads(Module.ALL_UNNAMED_MODULE, true);
 }

 /**
 * Updates this module to read another module without notifying the VM.
 *
 * @apiNote This method is for VM white-box testing.
 */
 void implAddReadsNoSync(Module other) {
 implAddReads(other, false);
 }

 /**
 * Makes the given {@code Module} readable to this module.
 *
 * If {@code syncVM} is {@code true} then the VM is notified.
 */
 private void implAddReads(Module other, boolean syncVM) {
 Objects.requireNonNull(other);
 if (!canRead(other)) {
 // update VM first, just in case it fails
 if (syncVM) {
 if (other == ALL_UNNAMED_MODULE) {
 addReads0(this, null);
 } else {
 addReads0(this, other);
 }
 }

 // add reflective read
 ReflectionData.reads.putIfAbsent(this, other, Boolean.TRUE);
 }
 }

 // -- exported and open packages --

 // the packages are open to other modules, can be null
 // if the value contains EVERYONE_MODULE then the package is open to all
 private volatile Map<String, Set<Module>> openPackages;

 // the packages that are exported, can be null
 // if the value contains EVERYONE_MODULE then the package is exported to all
 private volatile Map<String, Set<Module>> exportedPackages;

 /**
 * Returns {@code true} if this module exports the given package to at
 * least the given module.
 *
 * This method returns {@code true} if invoked to test if a package in
 * this module is exported to itself. It always returns {@code true} when
 * invoked on an unnamed module. A package that is {@link #isOpen open} to
 * the given module is considered exported to that module at run-time and
 * so this method returns {@code true} if the package is open to the given
 * module. 
 *
 * This method does not check if the given module reads this module. 
 *
 * @param pn
 * The package name
 * @param other
 * The other module
 *
 * @return {@code true} if this module exports the package to at least the
 * given module
 *
 * @see ModuleDescriptor#exports()
 * @see #addExports(String,Module)
 */
 public boolean isExported(String pn, Module other) {
 Objects.requireNonNull(pn);
 Objects.requireNonNull(other);
 return implIsExportedOrOpen(pn, other, /*open*/false);
 }

 /**
 * Returns {@code true} if this module has opened a package to at
 * least the given module.
 *
 * This method returns {@code true} if invoked to test if a package in
 * this module is open to itself. It returns {@code true} when invoked on an
 * {@link ModuleDescriptor#isOpen open} module with a package in the module.
 * It always returns {@code true} when invoked on an unnamed module. 
 *
 * This method does not check if the given module reads this module. 
 *
 * @param pn
 * The package name
 * @param other
 * The other module
 *
 * @return {@code true} if this module has opened the package
 * to at least the given module
 *
 * @see ModuleDescriptor#opens()
 * @see #addOpens(String,Module)
 * @see java.lang.reflect.AccessibleObject#setAccessible(boolean)
 * @see java.lang.invoke.MethodHandles#privateLookupIn
 */
 public boolean isOpen(String pn, Module other) {
 Objects.requireNonNull(pn);
 Objects.requireNonNull(other);
 return implIsExportedOrOpen(pn, other, /*open*/true);
 }

 /**
 * Returns {@code true} if this module exports the given package
 * unconditionally.
 *
 * This method always returns {@code true} when invoked on an unnamed
 * module. A package that is {@link #isOpen(String) opened} unconditionally
 * is considered exported unconditionally at run-time and so this method
 * returns {@code true} if the package is opened unconditionally. 
 *
 * This method does not check if the given module reads this module. 
 *
 * @param pn
 * The package name
 *
 * @return {@code true} if this module exports the package unconditionally
 *
 * @see ModuleDescriptor#exports()
 */
 public boolean isExported(String pn) {
 Objects.requireNonNull(pn);
 return implIsExportedOrOpen(pn, EVERYONE_MODULE, /*open*/false);
 }

 /**
 * Returns {@code true} if this module has opened a package
 * unconditionally.
 *
 * This method always returns {@code true} when invoked on an unnamed
 * module. Additionally, it always returns {@code true} when invoked on an
 * {@link ModuleDescriptor#isOpen open} module with a package in the
 * module. 
 *
 * This method does not check if the given module reads this module. 
 *
 * @param pn
 * The package name
 *
 * @return {@code true} if this module has opened the package
 * unconditionally
 *
 * @see ModuleDescriptor#opens()
 */
 public boolean isOpen(String pn) {
 Objects.requireNonNull(pn);
 return implIsExportedOrOpen(pn, EVERYONE_MODULE, /*open*/true);
 }

 /**
 * Returns {@code true} if this module exports or opens the given package
 * to the given module. If the other module is {@code EVERYONE_MODULE} then
 * this method tests if the package is exported or opened unconditionally.
 */
 private boolean implIsExportedOrOpen(String pn, Module other, boolean open) {
 // all packages in unnamed modules are open
 if (!isNamed())
 return true;

 // all packages are exported/open to self
 if (other == this && descriptor.packages().contains(pn))
 return true;

 // all packages in open and automatic modules are open
 if (descriptor.isOpen() || descriptor.isAutomatic())
 return descriptor.packages().contains(pn);

 // exported/opened via module declaration/descriptor
 if (isStaticallyExportedOrOpen(pn, other, open))
 return true;

 // exported via addExports/addOpens
 if (isReflectivelyExportedOrOpen(pn, other, open))
 return true;

 // not exported or open to other
 return false;
 }

 /**
 * Returns {@code true} if this module exports or opens a package to
 * the given module via its module declaration or CLI options.
 */
 private boolean isStaticallyExportedOrOpen(String pn, Module other, boolean open) {
 // test if package is open to everyone or <other>
 Map<String, Set<Module>> openPackages = this.openPackages;
 if (openPackages != null && allows(openPackages.get(pn), other)) {
 return true;
 }

 if (!open) {
 // test package is exported to everyone or <other>
 Map<String, Set<Module>> exportedPackages = this.exportedPackages;
 if (exportedPackages != null && allows(exportedPackages.get(pn), other)) {
 return true;
 }
 }

 return false;
 }

 /**
 * Returns {@code true} if targets is non-null and contains EVERYONE_MODULE
 * or the given module. Also returns true if the given module is an unnamed
 * module and targets contains ALL_UNNAMED_MODULE.
 */
 private boolean allows(Set<Module> targets, Module module) {
 if (targets != null) {
 if (targets.contains(EVERYONE_MODULE))
 return true;
 if (module != EVERYONE_MODULE) {
 if (targets.contains(module))
 return true;
 if (!module.isNamed() && targets.contains(ALL_UNNAMED_MODULE))
 return true;
 }
 }
 return false;
 }

 /**
 * Returns {@code true} if this module reflectively exports or opens the
 * given package to the given module.
 */
 private boolean isReflectivelyExportedOrOpen(String pn, Module other, boolean open) {
 // exported or open to all modules
 Map<String, Boolean> exports = ReflectionData.exports.get(this, EVERYONE_MODULE);
 if (exports != null) {
 Boolean b = exports.get(pn);
 if (b != null) {
 boolean isOpen = b.booleanValue();
 if (!open || isOpen) return true;
 }
 }

 if (other != EVERYONE_MODULE) {

 // exported or open to other
 exports = ReflectionData.exports.get(this, other);
 if (exports != null) {
 Boolean b = exports.get(pn);
 if (b != null) {
 boolean isOpen = b.booleanValue();
 if (!open || isOpen) return true;
 }
 }

 // other is an unnamed module && exported or open to all unnamed
 if (!other.isNamed()) {
 exports = ReflectionData.exports.get(this, ALL_UNNAMED_MODULE);
 if (exports != null) {
 Boolean b = exports.get(pn);
 if (b != null) {
 boolean isOpen = b.booleanValue();
 if (!open || isOpen) return true;
 }
 }
 }

 }

 return false;
 }

 /**
 * Returns {@code true} if this module reflectively exports the
 * given package to the given module.
 */
 boolean isReflectivelyExported(String pn, Module other) {
 return isReflectivelyExportedOrOpen(pn, other, false);
 }

 /**
 * Returns {@code true} if this module reflectively opens the
 * given package to the given module.
 */
 boolean isReflectivelyOpened(String pn, Module other) {
 return isReflectivelyExportedOrOpen(pn, other, true);
 }

 /**
 * If the caller's module is this module then update this module to export
 * the given package to the given module.
 *
 * This method has no effect if the package is already exported (or
 * open) to the given module. 
 *
 * @apiNote As specified in section {@jvms 5.4.3} of the <cite>The Java
 * Virtual Machine Specification </cite>, if an attempt to resolve a
 * symbolic reference fails because of a linkage error, then subsequent
 * attempts to resolve the reference always fail with the same error that
 * was thrown as a result of the initial resolution attempt.
 *
 * @param pn
 * The package name
 * @param other
 * The module
 *
 * @return this module
 *
 * @throws IllegalArgumentException
 * If {@code pn} is {@code null}, or this is a named module and the
 * package {@code pn} is not a package in this module
 * @throws IllegalCallerException
 * If this is a named module and the caller's module is not this
 * module
 *
 * @jvms 5.4.3 Resolution
 * @see #isExported(String,Module)
 */
 @CallerSensitive
 public Module addExports(String pn, Module other) {
 if (pn == null)
 throw new IllegalArgumentException("package is null");
 Objects.requireNonNull(other);

 if (isNamed()) {
 Module caller = getCallerModule(Reflection.getCallerClass());
 if (caller != this) {
 throw new IllegalCallerException(caller + " != " + this);
 }
 implAddExportsOrOpens(pn, other, /*open*/false, /*syncVM*/true);
 }

 return this;
 }

 /**
 * If this module has opened a package to at least the caller
 * module then update this module to open the package to the given module.
 * Opening a package with this method allows all types in the package,
 * and all their members, not just public types and their public members,
 * to be reflected on by the given module when using APIs that support
 * private access or a way to bypass or suppress default Java language
 * access control checks.
 *
 * This method has no effect if the package is already open
 * to the given module. 
 *
 * @apiNote This method can be used for cases where a consumer
 * module uses a qualified opens to open a package to an API
 * module but where the reflective access to the members of classes in
 * the consumer module is delegated to code in another module. Code in the
 * API module can use this method to open the package in the consumer module
 * to the other module.
 *
 * @param pn
 * The package name
 * @param other
 * The module
 *
 * @return this module
 *
 * @throws IllegalArgumentException
 * If {@code pn} is {@code null}, or this is a named module and the
 * package {@code pn} is not a package in this module
 * @throws IllegalCallerException
 * If this is a named module and this module has not opened the
 * package to at least the caller's module
 *
 * @see #isOpen(String,Module)
 * @see java.lang.reflect.AccessibleObject#setAccessible(boolean)
 * @see java.lang.invoke.MethodHandles#privateLookupIn
 */
 @CallerSensitive
 public Module addOpens(String pn, Module other) {
 if (pn == null)
 throw new IllegalArgumentException("package is null");
 Objects.requireNonNull(other);

 if (isNamed()) {
 Module caller = getCallerModule(Reflection.getCallerClass());
 if (caller != this && (caller == null || !isOpen(pn, caller)))
 throw new IllegalCallerException(pn + " is not open to " + caller);
 implAddExportsOrOpens(pn, other, /*open*/true, /*syncVM*/true);
 }

 return this;
 }

 /**
 * Updates this module to export a package unconditionally.
 *
 * @apiNote This method is for JDK tests only.
 */
 void implAddExports(String pn) {
 implAddExportsOrOpens(pn, Module.EVERYONE_MODULE, false, true);
 }

 /**
 * Updates this module to export a package to another module.
 *
 * @apiNote Used by Instrumentation::redefineModule and --add-exports
 */
 void implAddExports(String pn, Module other) {
 implAddExportsOrOpens(pn, other, false, true);
 }

 /**
 * Updates this module to export a package to all unnamed modules.
 *
 * @apiNote Used by the --add-exports command line option.
 */
 void implAddExportsToAllUnnamed(String pn) {
 implAddExportsOrOpens(pn, Module.ALL_UNNAMED_MODULE, false, true);
 }

 /**
 * Updates this export to export a package unconditionally without
 * notifying the VM.
 *
 * @apiNote This method is for VM white-box testing.
 */
 void implAddExportsNoSync(String pn) {
 implAddExportsOrOpens(pn.replace('/', '.'), Module.EVERYONE_MODULE, false, false);
 }

 /**
 * Updates a module to export a package to another module without
 * notifying the VM.
 *
 * @apiNote This method is for VM white-box testing.
 */
 void implAddExportsNoSync(String pn, Module other) {
 implAddExportsOrOpens(pn.replace('/', '.'), other, false, false);
 }

 /**
 * Updates this module to open a package unconditionally.
 *
 * @apiNote This method is for JDK tests only.
 */
 void implAddOpens(String pn) {
 implAddExportsOrOpens(pn, Module.EVERYONE_MODULE, true, true);
 }

 /**
 * Updates this module to open a package to another module.
 *
 * @apiNote Used by Instrumentation::redefineModule and --add-opens
 */
 void implAddOpens(String pn, Module other) {
 implAddExportsOrOpens(pn, other, true, true);
 }

 /**
 * Updates this module to open a package to all unnamed modules.
 *
 * @apiNote Used by the --add-opens command line option.
 */
 void implAddOpensToAllUnnamed(String pn) {
 implAddExportsOrOpens(pn, Module.ALL_UNNAMED_MODULE, true, true);
 }

 /**
 * Updates a module to export or open a module to another module.
 *
 * If {@code syncVM} is {@code true} then the VM is notified.
 */
 private void implAddExportsOrOpens(String pn,
 Module other,
 boolean open,
 boolean syncVM) {
 Objects.requireNonNull(other);
 Objects.requireNonNull(pn);

 // all packages are open in unnamed, open, and automatic modules
 if (!isNamed() || descriptor.isOpen() || descriptor.isAutomatic())
 return;

 // check if the package is already exported/open to other
 if (implIsExportedOrOpen(pn, other, open))
 return;

 // can only export a package in the module
 if (!descriptor.packages().contains(pn)) {
 throw new IllegalArgumentException("package " + pn
 + " not in contents");
 }

 // update VM first, just in case it fails
 if (syncVM) {
 if (other == EVERYONE_MODULE) {
 addExportsToAll0(this, pn);
 } else if (other == ALL_UNNAMED_MODULE) {
 addExportsToAllUnnamed0(this, pn);
 } else {
 addExports0(this, pn, other);
 }
 }

 // add package name to exports if absent
 Map<String, Boolean> map = ReflectionData.exports
 .computeIfAbsent(this, other,
 (m1, m2) -> new ConcurrentHashMap<>());
 if (open) {
 map.put(pn, Boolean.TRUE); // may need to promote from FALSE to TRUE
 } else {
 map.putIfAbsent(pn, Boolean.FALSE);
 }
 }

 /**
 * Updates a module to open all packages in the given sets to all unnamed
 * modules.
 *
 * @apiNote Used during startup to open packages for illegal access.
 */
 void implAddOpensToAllUnnamed(Set<String> concealedPkgs, Set<String> exportedPkgs) {
 if (jdk.internal.misc.VM.isModuleSystemInited()) {
 throw new IllegalStateException("Module system already initialized");
 }

 // replace this module's openPackages map with a new map that opens
 // the packages to all unnamed modules.
 Map<String, Set<Module>> openPackages = this.openPackages;
 if (openPackages == null) {
 openPackages = HashMap.newHashMap(concealedPkgs.size() + exportedPkgs.size());
 } else {
 openPackages = new HashMap<>(openPackages);
 }
 implAddOpensToAllUnnamed(concealedPkgs, openPackages);
 implAddOpensToAllUnnamed(exportedPkgs, openPackages);
 this.openPackages = openPackages;
 }

 private void implAddOpensToAllUnnamed(Set<String> pkgs, Map<String, Set<Module>> openPackages) {
 for (String pn : pkgs) {
 Set<Module> prev = openPackages.putIfAbsent(pn, ALL_UNNAMED_MODULE_SET);
 if (prev != null) {
 prev.add(ALL_UNNAMED_MODULE);
 }

 // update VM to export the package
 addExportsToAllUnnamed0(this, pn);
 }
 }

 // -- services --

 /**
 * If the caller's module is this module then update this module to add a
 * service dependence on the given service type. This method is intended
 * for use by frameworks that invoke {@link java.util.ServiceLoader
 * ServiceLoader} on behalf of other modules or where the framework is
 * passed a reference to the service type by other code. This method is
 * a no-op when invoked on an unnamed module or an automatic module.
 *
 * This method does not cause {@link Configuration#resolveAndBind
 * resolveAndBind} to be re-run. 
 *
 * @param service
 * The service type
 *
 * @return this module
 *
 * @throws IllegalCallerException
 * If this is a named module and the caller's module is not this
 * module
 *
 * @see #canUse(Class)
 * @see ModuleDescriptor#uses()
 */
 @CallerSensitive
 public Module addUses(Class<?> service) {
 Objects.requireNonNull(service);

 if (isNamed() && !descriptor.isAutomatic()) {
 Module caller = getCallerModule(Reflection.getCallerClass());
 if (caller != this) {
 throw new IllegalCallerException(caller + " != " + this);
 }
 implAddUses(service);
 }

 return this;
 }

 /**
 * Update this module to add a service dependence on the given service
 * type.
 */
 void implAddUses(Class<?> service) {
 if (!canUse(service)) {
 ReflectionData.uses.putIfAbsent(this, service, Boolean.TRUE);
 }
 }

 /**
 * Indicates if this module has a service dependence on the given service
 * type. This method always returns {@code true} when invoked on an unnamed
 * module or an automatic module.
 *
 * @param service
 * The service type
 *
 * @return {@code true} if this module uses service type {@code st}
 *
 * @see #addUses(Class)
 */
 public boolean canUse(Class<?> service) {
 Objects.requireNonNull(service);

 if (!isNamed())
 return true;

 if (descriptor.isAutomatic())
 return true;

 // uses was declared
 if (descriptor.uses().contains(service.getName()))
 return true;

 // uses added via addUses
 return ReflectionData.uses.containsKeyPair(this, service);
 }

 // -- packages --

 /**
 * Returns the set of package names for the packages in this module.
 *
 * For named modules, the returned set contains an element for each
 * package in the module. 
 *
 * For unnamed modules, the returned set contains an element for
 * each package that {@link ClassLoader#getDefinedPackages() has been defined}
 * in the unnamed module.
 *
 * @return the set of the package names of the packages in this module
 */
 public Set<String> getPackages() {
 if (isNamed()) {
 return descriptor.packages();
 } else {
 // unnamed module
 Stream<Package> packages;
 if (loader == null) {
 packages = BootLoader.packages();
 } else {
 packages = loader.packages();
 }
 return packages.filter(p -> p.module() == this)
 .map(Package::getName).collect(Collectors.toSet());
 }
 }

 // -- creating Module objects --

 /**
 * Defines all module in a configuration to the runtime.
 *
 * @return a map of module name to runtime {@code Module}
 *
 * @throws IllegalArgumentException
 * If the function maps a module to the null or platform class loader
 * @throws IllegalStateException
 * If the module cannot be defined to the VM or its packages overlap
 * with another module mapped to the same class loader
 */
 static Map<String, Module> defineModules(Configuration cf,
 Function<String, ClassLoader> clf,
 ModuleLayer layer)
 {
 boolean isBootLayer = (ModuleLayer.boot() == null);

 int numModules = cf.modules().size();
 Map<String, Module> nameToModule = HashMap.newHashMap(numModules);

 // to avoid repeated lookups and reduce iteration overhead, we create
 // arrays holding correlated information about each module.
 ResolvedModule[] resolvedModules = new ResolvedModule[numModules];
 Module[] modules = new Module[numModules];
 ClassLoader[] classLoaders = new ClassLoader[numModules];

 resolvedModules = cf.modules().toArray(resolvedModules);

 // record that we want to bind the layer to non-boot and non-platform
 // module loaders as a final step
 HashSet<ClassLoader> toBindLoaders = new HashSet<>(4);
 boolean hasPlatformModules = false;

 // map each module to a class loader
 ClassLoader pcl = ClassLoaders.platformClassLoader();
 boolean isModuleLoaderMapper = ModuleLoaderMap.isBuiltinMapper(clf);

 for (int index = 0; index < numModules; index++) {
 String name = resolvedModules[index].name();
 ClassLoader loader = clf.apply(name);

 if (loader == null || loader == pcl) {
 if (!isModuleLoaderMapper) {
 throw new IllegalArgumentException("loader can't be 'null'"
 + " or the platform class loader");
 }
 hasPlatformModules = true;
 } else {
 toBindLoaders.add(loader);
 }

 classLoaders[index] = loader;
 }

 // define each module in the configuration to the VM
 for (int index = 0; index < numModules; index++) {
 ModuleReference mref = resolvedModules[index].reference();
 ModuleDescriptor descriptor = mref.descriptor();
 String name = descriptor.name();
 ClassLoader loader = classLoaders[index];
 Module m;
 if (loader == null && name.equals("java.base")) {
 // java.base is already defined to the VM
 m = Object.class.getModule();
 } else {
 URI uri = mref.location().orElse(null);
 m = new Module(layer, loader, descriptor, uri);
 }
 nameToModule.put(name, m);
 modules[index] = m;
 }

 // setup readability and exports/opens
 for (int index = 0; index < numModules; index++) {
 ResolvedModule resolvedModule = resolvedModules[index];
 ModuleReference mref = resolvedModule.reference();
 ModuleDescriptor descriptor = mref.descriptor();
 Module m = modules[index];

 // reads
 Set<Module> reads = new HashSet<>();

 // name -> source Module when in parent layer
 Map<String, Module> nameToSource = Map.of();

 for (ResolvedModule other : resolvedModule.reads()) {
 Module m2 = null;
 if (other.configuration() == cf) {
 // this configuration
 m2 = nameToModule.get(other.name());
 assert m2 != null;
 } else {
 // parent layer
 for (ModuleLayer parent: layer.parents()) {
 m2 = findModule(parent, other);
 if (m2 != null)
 break;
 }
 assert m2 != null;
 if (nameToSource.isEmpty())
 nameToSource = new HashMap<>();
 nameToSource.put(other.name(), m2);
 }
 reads.add(m2);

 // update VM view
 addReads0(m, m2);
 }
 m.reads = reads;

 // automatic modules read all unnamed modules
 if (descriptor.isAutomatic()) {
 m.implAddReads(ALL_UNNAMED_MODULE, true);
 }

 // exports and opens, skipped for open and automatic
 if (!descriptor.isOpen() && !descriptor.isAutomatic()) {
 if (isBootLayer && descriptor.opens().isEmpty()) {
 // no open packages, no qualified exports to modules in parent layers
 initExports(m, nameToModule);
 } else {
 initExportsAndOpens(m, nameToSource, nameToModule, layer.parents());
 }
 }
 }

 // if there are modules defined to the boot or platform class loaders
 // then register the modules in the class loader's services catalog
 if (hasPlatformModules) {
 ServicesCatalog bootCatalog = BootLoader.getServicesCatalog();
 ServicesCatalog pclCatalog = ServicesCatalog.getServicesCatalog(pcl);
 for (int index = 0; index < numModules; index++) {
 ResolvedModule resolvedModule = resolvedModules[index];
 ModuleReference mref = resolvedModule.reference();
 ModuleDescriptor descriptor = mref.descriptor();
 if (!descriptor.provides().isEmpty()) {
 Module m = modules[index];
 ClassLoader loader = classLoaders[index];
 if (loader == null) {
 bootCatalog.register(m);
 } else if (loader == pcl) {
 pclCatalog.register(m);
 }
 }
 }
 }

 // record that there is a layer with modules defined to the class loader
 for (ClassLoader loader : toBindLoaders) {
 layer.bindToLoader(loader);
 }

 return nameToModule;
 }

 /**
 * Find the runtime Module corresponding to the given ResolvedModule
 * in the given parent layer (or its parents).
 */
 private static Module findModule(ModuleLayer parent,
 ResolvedModule resolvedModule) {
 Configuration cf = resolvedModule.configuration();
 String dn = resolvedModule.name();
 return parent.layers()
 .filter(l -> l.configuration() == cf)
 .findAny()
 .map(layer -> {
 Optional<Module> om = layer.findModule(dn);
 assert om.isPresent() : dn + " not found in layer";
 Module m = om.get();
 assert m.getLayer() == layer : m + " not in expected layer";
 return m;
 })
 .orElse(null);
 }

 /**
 * Initialize/setup a module's exports.
 *
 * @param m the module
 * @param nameToModule map of module name to Module (for qualified exports)
 */
 private static void initExports(Module m, Map<String, Module> nameToModule) {
 Map<String, Set<Module>> exportedPackages = new HashMap<>();

 for (Exports exports : m.getDescriptor().exports()) {
 String source = exports.source();
 if (exports.isQualified()) {
 // qualified exports
 Set<Module> targets = new HashSet<>();
 for (String target : exports.targets()) {
 Module m2 = nameToModule.get(target);
 if (m2 != null) {
 addExports0(m, source, m2);
 targets.add(m2);
 }
 }
 if (!targets.isEmpty()) {
 exportedPackages.put(source, targets);
 }
 } else {
 // unqualified exports
 addExportsToAll0(m, source);
 exportedPackages.put(source, EVERYONE_SET);
 }
 }

 if (!exportedPackages.isEmpty())
 m.exportedPackages = exportedPackages;
 }

 /**
 * Initialize/setup a module's exports.
 *
 * @param m the module
 * @param nameToSource map of module name to Module for modules that m reads
 * @param nameToModule map of module name to Module for modules in the layer
 * under construction
 * @param parents the parent layers
 */
 private static void initExportsAndOpens(Module m,
 Map<String, Module> nameToSource,
 Map<String, Module> nameToModule,
 List<ModuleLayer> parents) {
 ModuleDescriptor descriptor = m.getDescriptor();
 Map<String, Set<Module>> openPackages = new HashMap<>();
 Map<String, Set<Module>> exportedPackages = new HashMap<>();

 // process the open packages first
 for (Opens opens : descriptor.opens()) {
 String source = opens.source();

 if (opens.isQualified()) {
 // qualified opens
 Set<Module> targets = new HashSet<>();
 for (String target : opens.targets()) {
 Module m2 = findModule(target, nameToSource, nameToModule, parents);
 if (m2 != null) {
 addExports0(m, source, m2);
 targets.add(m2);
 }
 }
 if (!targets.isEmpty()) {
 openPackages.put(source, targets);
 }
 } else {
 // unqualified opens
 addExportsToAll0(m, source);
 openPackages.put(source, EVERYONE_SET);
 }
 }

 // next the exports, skipping exports when the package is open
 for (Exports exports : descriptor.exports()) {
 String source = exports.source();

 // skip export if package is already open to everyone
 Set<Module> openToTargets = openPackages.get(source);
 if (openToTargets != null && openToTargets.contains(EVERYONE_MODULE))
 continue;

 if (exports.isQualified()) {
 // qualified exports
 Set<Module> targets = new HashSet<>();
 for (String target : exports.targets()) {
 Module m2 = findModule(target, nameToSource, nameToModule, parents);
 if (m2 != null) {
 // skip qualified export if already open to m2
 if (openToTargets == null || !openToTargets.contains(m2)) {
 addExports0(m, source, m2);
 targets.add(m2);
 }
 }
 }
 if (!targets.isEmpty()) {
 exportedPackages.put(source, targets);
 }
 } else {
 // unqualified exports
 addExportsToAll0(m, source);
 exportedPackages.put(source, EVERYONE_SET);
 }
 }

 if (!openPackages.isEmpty())
 m.openPackages = openPackages;
 if (!exportedPackages.isEmpty())
 m.exportedPackages = exportedPackages;
 }

 /**
 * Find the runtime Module with the given name. The module name is the
 * name of a target module in a qualified exports or opens directive.
 *
 * @param target The target module to find
 * @param nameToSource The modules in parent layers that are read
 * @param nameToModule The modules in the layer under construction
 * @param parents The parent layers
 */
 private static Module findModule(String target,
 Map<String, Module> nameToSource,
 Map<String, Module> nameToModule,
 List<ModuleLayer> parents) {
 Module m = nameToSource.get(target);
 if (m == null) {
 m = nameToModule.get(target);
 if (m == null) {
 for (ModuleLayer parent : parents) {
 m = parent.findModule(target).orElse(null);
 if (m != null) break;
 }
 }
 }
 return m;
 }

 // -- annotations --

 /**
 * {@inheritDoc}
 * This method returns {@code null} when invoked on an unnamed module.
 *
 * Note that any annotation returned by this method is a
 * declaration annotation.
 */
 @Override
 public <T extends Annotation> T getAnnotation(Class<T> annotationClass) {
 return moduleInfoClass().getDeclaredAnnotation(annotationClass);
 }

 /**
 * {@inheritDoc}
 * This method returns an empty array when invoked on an unnamed module.
 *
 * Note that any annotations returned by this method are
 * declaration annotations.
 */
 @Override
 public Annotation[] getAnnotations() {
 return moduleInfoClass().getAnnotations();
 }

 /**
 * {@inheritDoc}
 * This method returns an empty array when invoked on an unnamed module.
 *
 * Note that any annotations returned by this method are
 * declaration annotations.
 */
 @Override
 public Annotation[] getDeclaredAnnotations() {
 return moduleInfoClass().getDeclaredAnnotations();
 }

 // cached class file with annotations
 private volatile Class<?> moduleInfoClass;

 @SuppressWarnings("removal")
 private Class<?> moduleInfoClass() {
 Class<?> clazz = this.moduleInfoClass;
 if (clazz != null)
 return clazz;

 synchronized (this) {
 clazz = this.moduleInfoClass;
 if (clazz == null) {
 if (isNamed()) {
 PrivilegedAction<Class<?>> pa = this::loadModuleInfoClass;
 clazz = AccessController.doPrivileged(pa);
 }
 if (clazz == null) {
 class DummyModuleInfo { }
 clazz = DummyModuleInfo.class;
 }
 this.moduleInfoClass = clazz;
 }
 return clazz;
 }
 }

 private Class<?> loadModuleInfoClass() {
 Class<?> clazz = null;
 try (InputStream in = getResourceAsStream("module-info.class")) {
 if (in != null)
 clazz = loadModuleInfoClass(in);
 } catch (Exception ignore) { }
 return clazz;
 }

 /**
 * Loads module-info.class as a package-private interface in a class loader
 * that is a child of this module's class loader.
 */
 private Class<?> loadModuleInfoClass(InputStream in) throws IOException {
 final String MODULE_INFO = "module-info";

 ClassWriter cw = new ClassWriter(ClassWriter.COMPUTE_MAXS
 + ClassWriter.COMPUTE_FRAMES);

 ClassVisitor cv = new ClassVisitor(Opcodes.ASM7, cw) {
 @Override
 public void visit(int version,
 int access,
 String name,
 String signature,
 String superName,
 String[] interfaces) {
 cw.visit(version,
 Opcodes.ACC_INTERFACE
 + Opcodes.ACC_ABSTRACT
 + Opcodes.ACC_SYNTHETIC,
 MODULE_INFO,
 null,
 "java/lang/Object",
 null);
 }
 @Override
 public AnnotationVisitor visitAnnotation(String desc, boolean visible) {
 // keep annotations
 return super.visitAnnotation(desc, visible);
 }
 @Override
 public void visitAttribute(Attribute attr) {
 // drop non-annotation attributes
 }
 @Override
 public ModuleVisitor visitModule(String name, int flags, String version) {
 // drop Module attribute
 return null;
 }
 };

 ClassReader cr = new ClassReader(in);
 cr.accept(cv, 0);
 byte[] bytes = cw.toByteArray();

 ClassLoader cl = new ClassLoader(loader) {
 @Override
 protected Class<?> findClass(String cn)throws ClassNotFoundException {
 if (cn.equals(MODULE_INFO)) {
 return super.defineClass(cn, bytes, 0, bytes.length);
 } else {
 throw new ClassNotFoundException(cn);
 }
 }
 @Override
 protected Class<?> loadClass(String cn, boolean resolve)
 throws ClassNotFoundException
 {
 synchronized (getClassLoadingLock(cn)) {
 Class<?> c = findLoadedClass(cn);
 if (c == null) {
 if (cn.equals(MODULE_INFO)) {
 c = findClass(cn);
 } else {
 c = super.loadClass(cn, resolve);
 }
 }
 if (resolve)
 resolveClass(c);
 return c;
 }
 }
 };

 try {
 return cl.loadClass(MODULE_INFO);
 } catch (ClassNotFoundException e) {
 throw new InternalError(e);
 }
 }

 // -- misc --

 /**
 * Returns an input stream for reading a resource in this module.
 * The {@code name} parameter is a {@code '/'}-separated path name that
 * identifies the resource. As with {@link Class#getResourceAsStream
 * Class.getResourceAsStream}, this method delegates to the module's class
 * loader {@link ClassLoader#findResource(String,String)
 * findResource(String,String)} method, invoking it with the module name
 * (or {@code null} when the module is unnamed) and the name of the
 * resource. If the resource name has a leading slash then it is dropped
 * before delegation.
 *
 * A resource in a named module may be encapsulated so that
 * it cannot be located by code in other modules. Whether a resource can be
 * located or not is determined as follows: 
 *
 * <ul>
 * <li> If the resource name ends with "{@code .class}" then it is not
 * encapsulated. </li>
 *
 * <li> A package name is derived from the resource name. If
 * the package name is a {@linkplain #getPackages() package} in the
 * module then the resource can only be located by the caller of this
 * method when the package is {@linkplain #isOpen(String,Module) open}
 * to at least the caller's module. If the resource is not in a
 * package in the module then the resource is not encapsulated. </li>
 * </ul>
 *
 * In the above, the package name for a resource is derived
 * from the subsequence of characters that precedes the last {@code '/'} in
 * the name and then replacing each {@code '/'} character in the subsequence
 * with {@code '.'}. A leading slash is ignored when deriving the package
 * name. As an example, the package name derived for a resource named
 * "{@code a/b/c/foo.properties}" is "{@code a.b.c}". A resource name
 * with the name "{@code META-INF/MANIFEST.MF}" is never encapsulated
 * because "{@code META-INF}" is not a legal package name. 
 *
 * This method returns {@code null} if the resource is not in this
 * module, the resource is encapsulated and cannot be located by the caller,
 * or access to the resource is denied by the security manager. 
 *
 * @param name
 * The resource name
 *
 * @return An input stream for reading the resource or {@code null}
 *
 * @throws IOException
 * If an I/O error occurs
 *
 * @see Class#getResourceAsStream(String)
 */
 @CallerSensitive
 public InputStream getResourceAsStream(String name) throws IOException {
 if (name.startsWith("/")) {
 name = name.substring(1);
 }

 if (isNamed() && Resources.canEncapsulate(name)) {
 Module caller = getCallerModule(Reflection.getCallerClass());
 if (caller != this && caller != Object.class.getModule()) {
 String pn = Resources.toPackageName(name);
 if (getPackages().contains(pn)) {
 if (caller == null) {
 if (!isOpen(pn)) {
 return null;
 }
 } else if (!isOpen(pn, caller)) {
 // package not open to caller
 return null;
 }
 }
 }
 }

 String mn = this.name;

 // special-case built-in class loaders to avoid URL connection
 if (loader == null) {
 return BootLoader.findResourceAsStream(mn, name);
 } else if (loader instanceof BuiltinClassLoader) {
 return ((BuiltinClassLoader) loader).findResourceAsStream(mn, name);
 }

 // locate resource in module
 URL url = loader.findResource(mn, name);
 if (url != null) {
 try {
 return url.openStream();
 } catch (SecurityException e) { }
 }

 return null;
 }

 /**
 * Returns the string representation of this module. For a named module,
 * the representation is the string {@code "module"}, followed by a space,
 * and then the module name. For an unnamed module, the representation is
 * the string {@code "unnamed module"}, followed by a space, and then an
 * implementation specific string that identifies the unnamed module.
 *
 * @return The string representation of this module
 */
 @Override
 public String toString() {
 if (isNamed()) {
 return "module " + name;
 } else {
 String id = Integer.toHexString(System.identityHashCode(this));
 return "unnamed module @" + id;
 }
 }

 /**
 * Returns the module that a given caller class is a member of. Returns
 * {@code null} if the caller is {@code null}.
 */
 private Module getCallerModule(Class<?> caller) {
 return (caller != null) ? caller.getModule() : null;
 }

 // -- native methods --

 // JVM_DefineModule
 private static native void defineModule0(Module module,
 boolean isOpen,
 String version,
 String location,
 Object[] pns);

 // JVM_AddReadsModule
 private static native void addReads0(Module from, Module to);

 // JVM_AddModuleExports
 private static native void addExports0(Module from, String pn, Module to);

 // JVM_AddModuleExportsToAll
 private static native void addExportsToAll0(Module from, String pn);

 // JVM_AddModuleExportsToAllUnnamed
 private static native void addExportsToAllUnnamed0(Module from, String pn);
}

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