深入学习Java动态代理

package common;
public class Test {
static interface Subject{
void sayHi();
void sayHello();
}
static class SubjectImpl implements Subject{
@Override
public void sayHi() {
System.out.println("hi");
}
@Override
public void sayHello() {
System.out.println("hello");
}
}
static class SubjectImplProxy implements Subject{
private Subject target;
public SubjectImplProxy(Subject target) {
this.target=target;
}
@Override
public void sayHi() {
System.out.print("say:");
target.sayHi();
}
@Override
public void sayHello() {
System.out.print("say:");
target.sayHello();
}
}
public static void main(String[] args) {
Subject subject=new SubjectImpl();
Subject subjectProxy=new SubjectImplProxy(subject);
subjectProxy.sayHi();
subjectProxy.sayHello();
}
}

package common;
import java.lang.invoke.MethodHandle;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
public class Test {
static interface Subject{
void sayHi();
void sayHello();
}
static class SubjectImpl implements Subject{
@Override
public void sayHi() {
System.out.println("hi");
}
@Override
public void sayHello() {
System.out.println("hello");
}
}
static class ProxyInvocationHandler implements InvocationHandler{
private Subject target;
public ProxyInvocationHandler(Subject target) {
this.target=target;
}
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
System.out.print("say:");
return method.invoke(target, args);
}
}
public static void main(String[] args) {
Subject subject=new SubjectImpl();
Subject subjectProxy=(Subject) Proxy.newProxyInstance(subject.getClass().getClassLoader(), subject.getClass().getInterfaces(), new ProxyInvocationHandler(subject));
subjectProxy.sayHi();
subjectProxy.sayHello();
}
}

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);　　//获取代理类的Class
/*
* Invoke its constructor with the designated invocation handler.
*/
try {
Constructor cons = cl.getConstructor(constructorParams);　　//constructorParams是写死的：{ InvocationHandler.class }，上边返回的代理类Class一定是extends Proxy的，而Proxy有一个参数为InvocationHandler的构造函数
return cons.newInstance(new Object[] { h });　　//这里通过构造函数将我们自己定义的InvocationHandler的子类传到代理类的实例里，当我们调用代理类的任何方法时，实际上都会调用我们定义的InvocationHandler子类重写的invoke()函数
} 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());
}
}

public static Class<?> getProxyClass(ClassLoader loader,
Class<?>... interfaces)
throws IllegalArgumentException
{
if (interfaces.length > 65535) {　　//因为在class文件中，一个类保存的接口数量是用2个字节来表示的，因此java中一个类最多可以实现65535个接口
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];
// for detecting duplicates
Set> interfaceSet = new HashSet<>();
　　　　 //验证interfaces里的接口是否能被类加载器加载，是否是接口，是否有重复的　
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.
*/
List key = Arrays.asList(interfaceNames);　　//使用interfaces列表作为key缓存在cache里，也就是实现了相同interfaces的代理类只会创建加载一次
/*
* Find or create the proxy class cache for the class loader.
*/
Map, Object> cache;
synchronized (loaderToCache) {
cache = 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.
*/
　　　　 //看看缓存里有没有，如果有就直接取出来然后return，否则判断根据pendingGenerationMarker判断是否有其它线程正在生成当前的代理类，如果有则cache.wait()等待，如果没有则创建。
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);
}
　　　　 //确认要生成的代理类所属的包，如果interfaces里所有接口都是public的，代理类所属包就是默认包；如果有interface不是public，那么所有不是public的interface必须在一个包里否则报错。
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;　　//生成代理类的名字，proxyPkg是上面确定下来的代理类所在的包名，proxyClassNamePrefix是写死的字符串“$Proxy”，num是一个全局唯一的long型数字，从0开始累积，每次生成新的代理类就+1，从这里也能看出生成的动态代理类的数量不能超过Long.maxValue
/*
* 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);　　//生成一个以proxyName为类名的，实现了Interfaces里所有接口的类的字节码
try {
proxyClass = defineClass0(loader, proxyName,
proxyClassFile, 0, proxyClassFile.length);　　//加载生成的类
} 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.
*/
　　　　　　　//创建成功，则将cache中该key的pendingGenerationMarker替换为实际的代理类的弱引用，否则也要清除pendingGenerationMarker标记；不管是否成功，都要执行cache.notifyAll()，让其它要创建相同代理类并且执行了cache.wait()的线程恢复执行。
synchronized (cache) {
if (proxyClass != null) {
cache.put(key, new WeakReference>(proxyClass));
} else {
cache.remove(key);
}
cache.notifyAll();
}
}
return proxyClass; //最后返回代理类Class
}

package common;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.lang.reflect.UndeclaredThrowableException;
public final class $Proxy0 extends Proxy
implements Test.Subject
{
private static Method m4;
private static Method m1;
private static Method m3;
private static Method m0;
private static Method m2;
static
{
try {
m4 = Class.forName("Test$Subject").getMethod("sayHello", new Class[0]);
m1 = Class.forName("java.lang.Object").getMethod("equals", new Class[] { Class.forName("java.lang.Object") });
m3 = Class.forName("Test$Subject").getMethod("sayHi", new Class[0]);
m0 = Class.forName("java.lang.Object").getMethod("hashCode", new Class[0]);
m2 = Class.forName("java.lang.Object").getMethod("toString", new Class[0]);
} catch (Exception e) {
throw new RuntimeException(e);
}
}
public $Proxy0(InvocationHandler paramInvocationHandler)
{
super(paramInvocationHandler);
}
public final void sayHello()
{
try
{
this.h.invoke(this, m4, null);
return;
}
catch (RuntimeException localRuntimeException)
{
throw localRuntimeException;
}
catch (Throwable localThrowable)
{
throw new UndeclaredThrowableException(localThrowable);
}
}
public final boolean equals(Object paramObject)
{
try
{
return ((Boolean)this.h.invoke(this, m1, new Object[] { paramObject })).booleanValue();
}
catch (RuntimeException localRuntimeException)
{
throw localRuntimeException;
}
catch (Throwable localThrowable)
{
throw new UndeclaredThrowableException(localThrowable);
}
}
public final void sayHi()
{
try
{
this.h.invoke(this, m3, null);
return;
}
catch (RuntimeException localRuntimeException)
{
throw localRuntimeException;
}
catch (Throwable localThrowable)
{
throw new UndeclaredThrowableException(localThrowable);
}
}
public final int hashCode()
{
try
{
return ((Integer)this.h.invoke(this, m0, null)).intValue();
}
catch (RuntimeException localRuntimeException)
{
throw localRuntimeException;
}
catch (Throwable localThrowable)
{
throw new UndeclaredThrowableException(localThrowable);
}
}
public final String toString()
{
try
{
return (String)this.h.invoke(this, m2, null);
}
catch (RuntimeException localRuntimeException)
{
throw localRuntimeException;
}
catch (Throwable localThrowable)
{
throw new UndeclaredThrowableException(localThrowable);
}
}
}