动态代理Proxy
接口：
package com.atb.proxy.simple;
public interface ProxyInterface {
public void methodPrint();
}
实现类：
package com.atb.proxy.simple;
public class ProxyImple implements ProxyInterface{
private String aa="sss";
public void methodPrint() {
System.out.println("hi dubbo:"+aa);
}
}
下面的是代理类及测试的具体代码
package com.atb.proxy.simple;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
/**
* 动态代理类
* @author xieronghui
*/
public class DynamicProxy implements InvocationHandler {
// 被代理对象
private Object proxyObject;
/**
* 绑定委托对象，并返回一个代理类
*/
public Object bind(Object proxyObject) {
this.proxyObject = proxyObject;
/**
* 这里是源码的方法描述 loader 代表动态加载的代理对象；
* interfaces 接口（一个类我们可以实现多个接口吧这里相当于ProxyInterface）
* h InvocationHandler（DynamicProxy 对象 实现了InvocationHandler）
* public static Object newProxyInstance(ClassLoader loader,
Class<?>[] interfaces,
InvocationHandler h)
*/
return Proxy.newProxyInstance(proxyObject.getClass().getClassLoader(),
proxyObject.getClass().getInterfaces(), this);
}
/**
* $Proxy0 调用父类的invoke
*/
public Object invoke(Object proxy, Method method, Object[] args)
throws Throwable {
Object result = method.invoke(proxyObject, args);
return result;
}
}
测试对象
package com.atb.proxy.simple;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
public class ProxyTest {
public static void main(String[] args) throws SecurityException, NoSuchMethodException {
DynamicProxy proxy=new DynamicProxy();
ProxyInterface proxyInter=(ProxyInterface)proxy.bind(new ProxyImple());
//proxyInter.methodPrint();
//这里可以通过运行结果证明proxyInter是Proxy的一个实例，这个实例实现了proxyInter接口
System.out.println(proxyInter instanceof Proxy);
//这里可以看出proxyInter的Class类是$Proxy0,这个$Proxy0类继承了Proxy，实现了proxyInter接口
System.out.println("ProxyInterface的Class类是："+proxyInter.getClass().toString());
System.out.print("ProxyInterface($Proxy0)中的属性有：");
Field[] field=proxyInter.getClass().getDeclaredFields();
for(Field f:field){
System.out.print(f.getName()+", ");
}
System.out.print("\n"+"ProxyInterface--->($Proxy0)中的方法有：");
Method[] method=proxyInter.getClass().getDeclaredMethods();
for(Method m:method){
System.out.print(m.getName()+", ");
}
System.out.println("\n"+"ProxyInterface ($Proxy0)的父类是："+proxyInter.getClass().getSuperclass());
System.out.print("\n"+"ProxyInterface ($Proxy0)实现的接口是：");
Class<?>[] interfaces=proxyInter.getClass().getInterfaces();
for(Class<?> i:interfaces){
System.out.print(i.getName()+", ");
}
System.out.println("\n"+"#调用的结果：");
proxyInter.methodPrint();
}
}
返回结果：
true ProxyInterface的Class类是：class $Proxy0 ProxyInterface($Proxy0)中的属性有：m1, m3, m0, m2, ProxyInterface--->($Proxy0)中的方法有：equals, toString, hashCode, methodPrint, ProxyInterface ($Proxy0)的父类是：class java.lang.reflect.Proxy ProxyInterface ($Proxy0)实现的接口是：com.atb.proxy.simple.ProxyInterface, #调用的结果： hi dubbo:sss
ProxyInterface的Class类是：class $Proxy0 从这里可以看出
ProxyInterface proxyInter=(ProxyInterface)proxy.bind(new ProxyImple());
返回的Class 居然是$Proxy0 并不是 接口实现ProxyImple 的字节码，以前我一直理解是ProxyImple的实例去调用它的方法methodPrint（）；其实它是通过类加载器动态的构造了$Proxy0 的对象，我们控制台打印可以看出
ProxyInterface--->($Proxy0)中的方法有：equals, toString, hashCode, methodPrint,
ProxyInterface ($Proxy0)的父类是：class java.lang.reflect.Proxy
而$Proxy0 是在什么时候构造出来的呢打开
public Object bind(Object proxyObject) {
this.proxyObject = proxyObject;
/**
* 这里是源码的方法描述 loader 代表动态加载的代理对象；
* interfaces 接口（一个类我们可以实现多个接口吧这里相当于ProxyInterface）
* h InvocationHandler（DynamicProxy 对象 实现了InvocationHandler）
* public static Object newProxyInstance(ClassLoader loader,
Class<?>[] interfaces,
InvocationHandler h)
*/
return Proxy.newProxyInstance(proxyObject.getClass().getClassLoader(),
proxyObject.getClass().getInterfaces(), this);
}
调用的newProxyInstance方法
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); //这里就动态获取到了$Proxy0对象
/*
* Invoke its constructor with the designated invocation handler.
*/
try {
Constructor cons = cl.getConstructor(constructorParams);
return (Object) cons.newInstance(new Object[] { h });
} catch (NoSuchMethodException e) {
throw new InternalError(e.toString());
} catch (IllegalAccessException e) {
throw new InternalError(e.toString());
} catch (InstantiationException e) {
throw new InternalError(e.toString());
} catch (InvocationTargetException e) {
throw new InternalError(e.toString());
}
}
getProxyClass()方法很长，可以直接打开JDK源码学习理解
这里执行了初始化$Proxy0对象
/** prefix for all proxy class names */
private final static String proxyClassNamePrefix = "$Proxy";
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);
$Proxy0类 实现了interfaces的接口,并继承了Proxy类
类加载器动态创建的$Proxy0
public final class $Proxy0 extends Proxy implements ProxyInterface{
private static Method m1;
private static Method m0;
private static Method m3;
private static Method m2;
static {
try {
m1 = Class.forName("java.lang.Object").getMethod("equals",
new Class[] { Class.forName("java.lang.Object") });
m0 = Class.forName("java.lang.Object").getMethod("hashCode",
new Class[0]);
m3 = Class.forName("java.lang.Object").getMethod("toString",
new Class[0]);
m2 = Class.forName(" com.atb.proxy.simple.ProxyImple").getMethod("methodPrint",
new Class[0]);
} catch (NoSuchMethodException nosuchmethodexception) {
throw new NoSuchMethodError(nosuchmethodexception.getMessage());
} catch (ClassNotFoundException classnotfoundexception) {
throw new NoClassDefFoundError(classnotfoundexception.getMessage());
}
} //static
public $Proxy0(InvocationHandler invocationhandler) {
super(invocationhandler);
}
@Override
public final boolean equals(Object obj) {
try {
return ((Boolean) super.h.invoke(this, m1, new Object[] { obj })) .booleanValue();
} catch (Throwable throwable) {
throw new UndeclaredThrowableException(throwable);
}
}
@Override
public final int hashCode() {
try {
return ((Integer) super.h.invoke(this, m0, null)).intValue();
} catch (Throwable throwable) {
throw new UndeclaredThrowableException(throwable);
}
}
public final void methodPrint() {
try {
super.h.invoke(this, m2, null);
return;
} catch (Error e) {
} catch (Throwable throwable) {
throw new UndeclaredThrowableException(throwable);
}
}
@Override
public final String toString() {
try {
return (String) super.h.invoke(this, m3, null);
} catch (Throwable throwable) {
throw new UndeclaredThrowableException(throwable);
}
}
}
我们继续newProxyInstance 方法
Constructor cons = cl.getConstructor(constructorParams); //获取带参构造器
return (Object) cons.newInstance(new Object[] { h }); //实例化 并传参实例
这两句代码相当于
class Proxy{
InvocationHandler h=null;
protected Proxy(InvocationHandler h) {
this.h = h;
}
}
总结：实现的InvocationHandler 接口invoke 到底什么时候调用
public Object invoke(Object proxy, Method method, Object[] args)
throws Throwable {
Object result = method.invoke(proxyObject, args);
return result;
}
$Proxy0实例---》ProxyInterface，将引用赋给ProxyInterface。执行ProxyInterface方法时，调用了$Proxy0类中的methodPrint()方法，进而调用父类Proxy中的h的invoke()方法.即InvocationHandler.invoke()。