/*
* @(#)Proxy.java 1.22 05/11/17
*
* Copyright 2006 Sun Microsystems, Inc. All rights reserved.
* SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*/
package java.lang.reflect;
import java.lang.ref.Reference;
import java.lang.ref.WeakReference;
import java.util.Arrays;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;
import java.util.WeakHashMap;
import sun.misc.ProxyGenerator;
/**
* <code>Proxy</code> provides static methods for creating dynamic proxy
* classes and instances, and it is also the superclass of all
* dynamic proxy classes created by those methods.
*
* <p>To create a proxy for some interface <code>Foo</code>:
* <pre>
* InvocationHandler handler = new MyInvocationHandler(...);
* Class proxyClass = Proxy.getProxyClass(
* Foo.class.getClassLoader(), new Class[] { Foo.class });
* Foo f = (Foo) proxyClass.
* getConstructor(new Class[] { InvocationHandler.class }).
* newInstance(new Object[] { handler });
* </pre>
* or more simply:
* <pre>
* Foo f = (Foo) Proxy.newProxyInstance(Foo.class.getClassLoader(),
* new Class[] { Foo.class },
* handler);
* </pre>
*
* <p>A <i>dynamic proxy class</i> (simply referred to as a <i>proxy
* class</i> below) is a class that implements a list of interfaces
* specified at runtime when the class is created, with behavior as
* described below.
*
* A <i>proxy interface</i> is such an interface that is implemented
* by a proxy class.
*
* A <i>proxy instance</i> is an instance of a proxy class.
*
* Each proxy instance has an associated <i>invocation handler</i>
* object, which implements the interface {@link InvocationHandler}.
* A method invocation on a proxy instance through one of its proxy
* interfaces will be dispatched to the {@link InvocationHandler#invoke
* invoke} method of the instance's invocation handler, passing the proxy
* instance, a <code>java.lang.reflect.Method</code> object identifying
* the method that was invoked, and an array of type <code>Object</code>
* containing the arguments. The invocation handler processes the
* encoded method invocation as appropriate and the result that it
* returns will be returned as the result of the method invocation on
* the proxy instance.
*
* <p>A proxy class has the following properties:
*
* <ul>
* <li>Proxy classes are public, final, and not abstract.
*
* <li>The unqualified name of a proxy class is unspecified. The space
* of class names that begin with the string <code>"$Proxy"</code>
* should be, however, reserved for proxy classes.
*
* <li>A proxy class extends <code>java.lang.reflect.Proxy</code>.
*
* <li>A proxy class implements exactly the interfaces specified at its
* creation, in the same order.
*
* <li>If a proxy class implements a non-public interface, then it will
* be defined in the same package as that interface. Otherwise, the
* package of a proxy class is also unspecified. Note that package
* sealing will not prevent a proxy class from being successfully defined
* in a particular package at runtime, and neither will classes already
* defined by the same class loader and the same package with particular
* signers.
*
* <li>Since a proxy class implements all of the interfaces specified at
* its creation, invoking <code>getInterfaces</code> on its
* <code>Class</code> object will return an array containing the same
* list of interfaces (in the order specified at its creation), invoking
* <code>getMethods</code> on its <code>Class</code> object will return
* an array of <code>Method</code> objects that include all of the
* methods in those interfaces, and invoking <code>getMethod</code> will
* find methods in the proxy interfaces as would be expected.
*
* <li>The {@link Proxy#isProxyClass Proxy.isProxyClass} method will
* return true if it is passed a proxy class-- a class returned by
* <code>Proxy.getProxyClass</code> or the class of an object returned by
* <code>Proxy.newProxyInstance</code>-- and false otherwise.
*
* <li>The <code>java.security.ProtectionDomain</code> of a proxy class
* is the same as that of system classes loaded by the bootstrap class
* loader, such as <code>java.lang.Object</code>, because the code for a
* proxy class is generated by trusted system code. This protection
* domain will typically be granted
* <code>java.security.AllPermission</code>.
*
* <li>Each proxy class has one public constructor that takes one argument,
* an implementation of the interface {@link InvocationHandler}, to set
* the invocation handler for a proxy instance. Rather than having to use
* the reflection API to access the public constructor, a proxy instance
* can be also be created by calling the {@link Proxy#newProxyInstance
* Proxy.newInstance} method, which combines the actions of calling
* {@link Proxy#getProxyClass Proxy.getProxyClass} with invoking the
* constructor with an invocation handler.
* </ul>
*
* <p>A proxy instance has the following properties:
*
* <ul>
* <li>Given a proxy instance <code>proxy</code> and one of the
* interfaces implemented by its proxy class <code>Foo</code>, the
* following expression will return true:
* <pre>
* <code>proxy instanceof Foo</code>
* </pre>
* and the following cast operation will succeed (rather than throwing
* a <code>ClassCastException</code>):
* <pre>
* <code>(Foo) proxy</code>
* </pre>
*
* <li>Each proxy instance has an associated invocation handler, the one
* that was passed to its constructor. The static
* {@link Proxy#getInvocationHandler Proxy.getInvocationHandler} method
* will return the invocation handler associated with the proxy instance
* passed as its argument.
*
* <li>An interface method invocation on a proxy instance will be
* encoded and dispatched to the invocation handler's {@link
* InvocationHandler#invoke invoke} method as described in the
* documentation for that method.
*
* <li>An invocation of the <code>hashCode</code>,
* <code>equals</code>, or <code>toString</code> methods declared in
* <code>java.lang.Object</code> on a proxy instance will be encoded and
* dispatched to the invocation handler's <code>invoke</code> method in
* the same manner as interface method invocations are encoded and
* dispatched, as described above. The declaring class of the
* <code>Method</code> object passed to <code>invoke</code> will be
* <code>java.lang.Object</code>. Other public methods of a proxy
* instance inherited from <code>java.lang.Object</code> are not
* overridden by a proxy class, so invocations of those methods behave
* like they do for instances of <code>java.lang.Object</code>.
* </ul>
*
* <h3>Methods Duplicated in Multiple Proxy Interfaces</h3>
*
* <p>When two or more interfaces of a proxy class contain a method with
* the same name and parameter signature, the order of the proxy class's
* interfaces becomes significant. When such a <i>duplicate method</i>
* is invoked on a proxy instance, the <code>Method</code> object passed
* to the invocation handler will not necessarily be the one whose
* declaring class is assignable from the reference type of the interface
* that the proxy's method was invoked through. This limitation exists
* because the corresponding method implementation in the generated proxy
* class cannot determine which interface it was invoked through.
* Therefore, when a duplicate method is invoked on a proxy instance,
* the <code>Method</code> object for the method in the foremost interface
* that contains the method (either directly or inherited through a
* superinterface) in the proxy class's list of interfaces is passed to
* the invocation handler's <code>invoke</code> method, regardless of the
* reference type through which the method invocation occurred.
*
* <p>If a proxy interface contains a method with the same name and
* parameter signature as the <code>hashCode</code>, <code>equals</code>,
* or <code>toString</code> methods of <code>java.lang.Object</code>,
* when such a method is invoked on a proxy instance, the
* <code>Method</code> object passed to the invocation handler will have
* <code>java.lang.Object</code> as its declaring class. In other words,
* the public, non-final methods of <code>java.lang.Object</code>
* logically precede all of the proxy interfaces for the determination of
* which <code>Method</code> object to pass to the invocation handler.
*
* <p>Note also that when a duplicate method is dispatched to an
* invocation handler, the <code>invoke</code> method may only throw
* checked exception types that are assignable to one of the exception
* types in the <code>throws</code> clause of the method in <i>all</i> of
* the proxy interfaces that it can be invoked through. If the
* <code>invoke</code> method throws a checked exception that is not
* assignable to any of the exception types declared by the method in one
* of the proxy interfaces that it can be invoked through, then an
* unchecked <code>UndeclaredThrowableException</code> will be thrown by
* the invocation on the proxy instance. This restriction means that not
* all of the exception types returned by invoking
* <code>getExceptionTypes</code> on the <code>Method</code> object
* passed to the <code>invoke</code> method can necessarily be thrown
* successfully by the <code>invoke</code> method.
*
* @author Peter Jones
* @version 1.22, 05/11/17
* @see InvocationHandler
* @since 1.3
*/
public class Proxy implements java.io.Serializable {
private static final long serialVersionUID = -2222568056686623797L;
/** prefix for all proxy class names */
private final static String proxyClassNamePrefix = "$Proxy";
/** parameter types of a proxy class constructor */
private final static Class[] constructorParams =
{ InvocationHandler.class };
/** maps a class loader to the proxy class cache for that loader */
private static Map loaderToCache = new WeakHashMap();
/** marks that a particular proxy class is currently being generated */
private static Object pendingGenerationMarker = new Object();
/** next number to use for generation of unique proxy class names */
private static long nextUniqueNumber = 0;
private static Object nextUniqueNumberLock = new Object();
/** set of all generated proxy classes, for isProxyClass implementation */
private static Map proxyClasses =
Collections.synchronizedMap(new WeakHashMap());
/**
* the invocation handler for this proxy instance.
* @serial
*/
protected InvocationHandler h;
/**
* Prohibits instantiation.
*/
private Proxy() {
}
/**
* Constructs a new <code>Proxy</code> instance from a subclass
* (typically, a dynamic proxy class) with the specified value
* for its invocation handler.
*
* @param h the invocation handler for this proxy instance
*/
protected Proxy(InvocationHandler h) {
this.h = h;
}
/**
* Returns the <code>java.lang.Class</code> object for a proxy class
* given a class loader and an array of interfaces. The proxy class
* will be defined by the specified class loader and will implement
* all of the supplied interfaces. If a proxy class for the same
* permutation of interfaces has already been defined by the class
* loader, then the existing proxy class will be returned; otherwise,
* a proxy class for those interfaces will be generated dynamically
* and defined by the class loader.
*
* <p>There are several restrictions on the parameters that may be
* passed to <code>Proxy.getProxyClass</code>:
*
* <ul>
* <li>All of the <code>Class</code> objects in the
* <code>interfaces</code> array must represent interfaces, not
* classes or primitive types.
*
* <li>No two elements in the <code>interfaces</code> array may
* refer to identical <code>Class</code> objects.
*
* <li>All of the interface types must be visible by name through the
* specified class loader. In other words, for class loader
* <code>cl</code> and every interface <code>i</code>, the following
* expression must be true:
* <pre>
* Class.forName(i.getName(), false, cl) == i
* </pre>
*
* <li>All non-public interfaces must be in the same package;
* otherwise, it would not be possible for the proxy class to
* implement all of the interfaces, regardless of what package it is
* defined in.
*
* <li>For any set of member methods of the specified interfaces
* that have the same signature:
* <ul>
* <li>If the return type of any of the methods is a primitive
* type or void, then all of the methods must have that same
* return type.
* <li>Otherwise, one of the methods must have a return type that
* is assignable to all of the return types of the rest of the
* methods.
* </ul>
*
* <li>The resulting proxy class must not exceed any limits imposed
* on classes by the virtual machine. For example, the VM may limit
* the number of interfaces that a class may implement to 65535; in
* that case, the size of the <code>interfaces</code> array must not
* exceed 65535.
* </ul>
*
* <p>If any of these restrictions are violated,
* <code>Proxy.getProxyClass</code> will throw an
* <code>IllegalArgumentException</code>. If the <code>interfaces</code>
* array argument or any of its elements are <code>null</code>, a
* <code>NullPointerException</code> will be thrown.
*
* <p>Note that the order of the specified proxy interfaces is
* significant: two requests for a proxy class with the same combination
* of interfaces but in a different order will result in two distinct
* proxy classes.
*
* @param loader the class loader to define the proxy class
* @param interfaces the list of interfaces for the proxy class
* to implement
* @return a proxy class that is defined in the specified class loader
* and that implements the specified interfaces
* @throws IllegalArgumentException if any of the restrictions on the
* parameters that may be passed to <code>getProxyClass</code>
* are violated
* @throws NullPointerException if the <code>interfaces</code> array
* argument or any of its elements are <code>null</code>
*/
public static Class<?> getProxyClass(ClassLoader loader,
Class<?>... interfaces)
throws IllegalArgumentException
{
if (interfaces.length > 65535) {
throw new IllegalArgumentException("interface limit exceeded");
}
Class proxyClass = null;
/* collect interface names to use as key for proxy class cache */
String[] interfaceNames = new String[interfaces.length];
Set interfaceSet = new HashSet(); // for detecting duplicates
for (int i = 0; i < interfaces.length; i++) {
/*
* Verify that the class loader resolves the name of this
* interface to the same Class object.
*/
String interfaceName = interfaces[i].getName();
Class interfaceClass = null;
try {
interfaceClass = Class.forName(interfaceName, false, loader);
} catch (ClassNotFoundException e) {
}
if (interfaceClass != interfaces[i]) {
throw new IllegalArgumentException(
interfaces[i] + " is not visible from class loader");
}
/*
* Verify that the Class object actually represents an
* interface.
*/
if (!interfaceClass.isInterface()) {
throw new IllegalArgumentException(
interfaceClass.getName() + " is not an interface");
}
/*
* Verify that this interface is not a duplicate.
*/
if (interfaceSet.contains(interfaceClass)) {
throw new IllegalArgumentException(
"repeated interface: " + interfaceClass.getName());
}
interfaceSet.add(interfaceClass);
interfaceNames[i] = interfaceName;
}
/*
* Using string representations of the proxy interfaces as
* keys in the proxy class cache (instead of their Class
* objects) is sufficient because we require the proxy
* interfaces to be resolvable by name through the supplied
* class loader, and it has the advantage that using a string
* representation of a class makes for an implicit weak
* reference to the class.
*/
Object key = Arrays.asList(interfaceNames);
/*
* Find or create the proxy class cache for the class loader.
*/
Map cache;
synchronized (loaderToCache) {
cache = (Map) loaderToCache.get(loader);
if (cache == null) {
cache = new HashMap();
loaderToCache.put(loader, cache);
}
/*
* This mapping will remain valid for the duration of this
* method, without further synchronization, because the mapping
* will only be removed if the class loader becomes unreachable.
*/
}
/*
* Look up the list of interfaces in the proxy class cache using
* the key. This lookup will result in one of three possible
* kinds of values:
* null, if there is currently no proxy class for the list of
* interfaces in the class loader,
* the pendingGenerationMarker object, if a proxy class for the
* list of interfaces is currently being generated,
* or a weak reference to a Class object, if a proxy class for
* the list of interfaces has already been generated.
*/
synchronized (cache) {
/*
* Note that we need not worry about reaping the cache for
* entries with cleared weak references because if a proxy class
* has been garbage collected, its class loader will have been
* garbage collected as well, so the entire cache will be reaped
* from the loaderToCache map.
*/
do {
Object value = cache.get(key);
if (value instanceof Reference) {
proxyClass = (Class) ((Reference) value).get();
}
if (proxyClass != null) {
// proxy class already generated: return it
return proxyClass;
} else if (value == pendingGenerationMarker) {
// proxy class being generated: wait for it
try {
cache.wait();
} catch (InterruptedException e) {
/*
* The class generation that we are waiting for should
* take a small, bounded time, so we can safely ignore
* thread interrupts here.
*/
}
continue;
} else {
/*
* No proxy class for this list of interfaces has been
* generated or is being generated, so we will go and
* generate it now. Mark it as pending generation.
*/
cache.put(key, pendingGenerationMarker);
break;
}
} while (true);
}
try {
String proxyPkg = null; // package to define proxy class in
/*
* Record the package of a non-public proxy interface so that the
* proxy class will be defined in the same package. Verify that
* all non-public proxy interfaces are in the same package.
*/
for (int i = 0; i < interfaces.length; i++) {
int flags = interfaces[i].getModifiers();
if (!Modifier.isPublic(flags)) {
String name = interfaces[i].getName();
int n = name.lastIndexOf('.');
String pkg = ((n == -1) ? "" : name.substring(0, n + 1));
if (proxyPkg == null) {
proxyPkg = pkg;
} else if (!pkg.equals(proxyPkg)) {
throw new IllegalArgumentException(
"non-public interfaces from different packages");
}
}
}
if (proxyPkg == null) { // if no non-public proxy interfaces,
proxyPkg = ""; // use the unnamed package
}
{
/*
* Choose a name for the proxy class to generate.
*/
long num;
synchronized (nextUniqueNumberLock) {
num = nextUniqueNumber++;
}
String proxyName = proxyPkg + proxyClassNamePrefix + num;
/*
* Verify that the class loader hasn't already
* defined a class with the chosen name.
*/
/*
* Generate the specified proxy class.
*/
byte[] proxyClassFile = ProxyGenerator.generateProxyClass(
proxyName, interfaces);
try {
proxyClass = defineClass0(loader, proxyName,
proxyClassFile, 0, proxyClassFile.length);
} catch (ClassFormatError e) {
/*
* A ClassFormatError here means that (barring bugs in the
* proxy class generation code) there was some other
* invalid aspect of the arguments supplied to the proxy
* class creation (such as virtual machine limitations
* exceeded).
*/
throw new IllegalArgumentException(e.toString());
}
}
// add to set of all generated proxy classes, for isProxyClass
proxyClasses.put(proxyClass, null);
} finally {
/*
* We must clean up the "pending generation" state of the proxy
* class cache entry somehow. If a proxy class was successfully
* generated, store it in the cache (with a weak reference);
* otherwise, remove the reserved entry. In all cases, notify
* all waiters on reserved entries in this cache.
*/
synchronized (cache) {
if (proxyClass != null) {
cache.put(key, new WeakReference(proxyClass));
} else {
cache.remove(key);
}
cache.notifyAll();
}
}
return proxyClass;
}
/**
* Returns an instance of a proxy class for the specified interfaces
* that dispatches method invocations to the specified invocation
* handler. This method is equivalent to:
* <pre>
* Proxy.getProxyClass(loader, interfaces).
* getConstructor(new Class[] { InvocationHandler.class }).
* newInstance(new Object[] { handler });
* </pre>
*
* <p><code>Proxy.newProxyInstance</code> throws
* <code>IllegalArgumentException</code> for the same reasons that
* <code>Proxy.getProxyClass</code> does.
*
* @param loader the class loader to define the proxy class
* @param interfaces the list of interfaces for the proxy class
* to implement
* @param h the invocation handler to dispatch method invocations to
* @return a proxy instance with the specified invocation handler of a
* proxy class that is defined by the specified class loader
* and that implements the specified interfaces
* @throws IllegalArgumentException if any of the restrictions on the
* parameters that may be passed to <code>getProxyClass</code>
* are violated
* @throws NullPointerException if the <code>interfaces</code> array
* argument or any of its elements are <code>null</code>, or
* if the invocation handler, <code>h</code>, is
* <code>null</code>
*/
public static Object newProxyInstance(ClassLoader loader,
Class<?>[] interfaces,
InvocationHandler h)
throws IllegalArgumentException
{
if (h == null) {
throw new NullPointerException();
}
/*
* Look up or generate the designated proxy class.
*/
Class cl = getProxyClass(loader, interfaces);
/*
* Invoke its constructor with the designated invocation handler.
*/
try {
Constructor cons = cl.getConstructor(constructorParams);
return (Object) cons.newInstance(new Object[] { h });
} catch (NoSuchMethodException e) {
throw new InternalError(e.toString());
} catch (IllegalAccessException e) {
throw new InternalError(e.toString());
} catch (InstantiationException e) {
throw new InternalError(e.toString());
} catch (InvocationTargetException e) {
throw new InternalError(e.toString());
}
}
/**
* Returns true if and only if the specified class was dynamically
* generated to be a proxy class using the <code>getProxyClass</code>
* method or the <code>newProxyInstance</code> method.
*
* <p>The reliability of this method is important for the ability
* to use it to make security decisions, so its implementation should
* not just test if the class in question extends <code>Proxy</code>.
*
* @param cl the class to test
* @return <code>true</code> if the class is a proxy class and
* <code>false</code> otherwise
* @throws NullPointerException if <code>cl</code> is <code>null</code>
*/
public static boolean isProxyClass(Class<?> cl) {
if (cl == null) {
throw new NullPointerException();
}
return proxyClasses.containsKey(cl);
}
/**
* Returns the invocation handler for the specified proxy instance.
*
* @param proxy the proxy instance to return the invocation handler for
* @return the invocation handler for the proxy instance
* @throws IllegalArgumentException if the argument is not a
* proxy instance
*/
public static InvocationHandler getInvocationHandler(Object proxy)
throws IllegalArgumentException
{
/*
* Verify that the object is actually a proxy instance.
*/
if (!isProxyClass(proxy.getClass())) {
throw new IllegalArgumentException("not a proxy instance");
}
Proxy p = (Proxy) proxy;
return p.h;
}
private static native Class defineClass0(ClassLoader loader, String name,
byte[] b, int off, int len);
}
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