proxy.java

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    public static Class getProxyClass(ClassLoader loader, 
				      Class[] interfaces)
	throws IllegalArgumentException
    {
	Class proxyClass = null;

	/* buffer to generate string key for proxy class cache */
	StringBuffer keyBuffer = new StringBuffer();

	for (int i = 0; i < interfaces.length; i++) {
	    /*
	     * Verify that the class loader resolves the name of this
	     * interface to the same Class object.
	     */
	    Class interfaceClass = null;
	    try {
		interfaceClass =
		    Class.forName(interfaces[i].getName(), 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");
	    }

	    // continue building string key for proxy class cache
	    keyBuffer.append(interfaces[i].getName()).append(';');
	}

	/*
	 * Using a string representation of the proxy interfaces as keys
	 * in the proxy class cache instead of a collection of their Class
	 * objects is sufficiently correct because we require the proxy
	 * interfaces to be resolvable by name through the supplied class
	 * loader, and it has a couple of advantages: matching String
	 * objects is simpler and faster than matching collections of
	 * objects, and using a string representation of a class makes
	 * for an implicit weak reference to the class.
	 */
	String key = keyBuffer.toString();

	/*
	 * 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(3);
		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 string 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);
}