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什么是代理
代理是一种常用的设计模式，其目的就是为其他对象提供一个代理以控制对某个对象的访问。通过代理类这中间一层，能有效控制对委托类对象的直接访问，也可以很好地隐藏和保护委托类对象，同时也为实施不同控制策略预留了空间，从而在设计上获得了更大的灵活性。
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什么是动态代理
在运行时生成的class。
动态代理步骤：
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创建一个实现接口InvocationHandler的类，它必须实现invoke方法
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创建被代理的类以及接口
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通过Proxy的静态方法 newProxyInstance(ClassLoader loader, Class[] interfaces, InvocationHandler h)创建一个代理
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通过代理调用方法
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jdk的动态代理使用
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需要动态代理的接口：
public interface Subject { public String SayHello(String name); public String SayGoodBye(); } -
需要代理的实际对象
public class RealSubject implements Subject { public String SayHello(String name) { return "hello " + name; } public String SayGoodBye() { return " good bye "; } } -
调用处理器实现类（有木有感觉这里就是传说中的AOP啊）
import java.lang.reflect.InvocationHandler; import java.lang.reflect.Method; public class InvocationHandlerImpl implements InvocationHandler { private Object subject; public InvocationHandlerImpl(Object subject) { this.subject = subject; } public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { //在代理真实对象前我们可以添加一些自己的操作 System.out.println("在调用之前，我要干点啥呢？"); System.out.println("Method:" + method); //当代理对象调用真实对象的方法时，其会自动的跳转到代理对象关联的handler对象的invoke方法来进行调用 Object returnValue = method.invoke(subject, args); //在代理真实对象后我们也可以添加一些自己的操作 System.out.println("在调用之后，我要干点啥呢？"); return returnValue; } } -
测试
import java.lang.reflect.InvocationHandler; import java.lang.reflect.Proxy; public class DynamicProxyDemonstration { public static void main(String[] args) { //代理的真实对象 Subject realSubject = new RealSubject(); InvocationHandler handler = new InvocationHandlerImpl(realSubject); ClassLoader loader = realSubject.getClass().getClassLoader(); Class[] interfaces = realSubject.getClass().getInterfaces(); Subject subject = (Subject) Proxy.newProxyInstance(loader, interfaces, handler); System.out.println("动态代理对象的类型："+subject.getClass().getName()); String hello = subject.SayHello("jiankunking"); System.out.println(hello); // String goodbye = subject.SayGoodBye(); // System.out.println(goodbye); } }
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4. 动态代理实现
动态生成代理类：
通过ProxyGenerator.generateProxyClass(name,new Class[]{Subject.class})查看生成的字节码：
import sun.misc.ProxyGenerator;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Proxy;
public class DynamicProxyDemonstration
{
public static void main(String[] args)
{
//代理的真实对象
Subject realSubject = new RealSubject();
InvocationHandler handler = new InvocationHandlerImpl(realSubject);
ClassLoader loader = handler.getClass().getClassLoader();
Class[] interfaces = realSubject.getClass().getInterfaces();
Subject subject = (Subject) Proxy.newProxyInstance(loader, interfaces, handler);
System.out.println("动态代理对象的类型："+subject.getClass().getName());
String hello = subject.SayHello("jiankunking");
System.out.println(hello);
// 将生成的字节码保存到本地，
createProxyClassFile();
}
private static void createProxyClassFile(){
String name = "ProxySubject";
byte[] data = ProxyGenerator.generateProxyClass(name,new Class[]{Subject.class});
FileOutputStream out =null;
try {
out = new FileOutputStream(name+".class");
System.out.println((new File("hello")).getAbsolutePath());
out.write(data);
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}finally {
if(null!=out) try {
out.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
用jd-jui 工具将生成的字节码反编译：
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.lang.reflect.UndeclaredThrowableException;
import jiankunking.Subject;
public final class ProxySubject
extends Proxy
implements Subject
{
private static Method m1;
private static Method m3;
private static Method m4;
private static Method m2;
private static Method m0;
public ProxySubject(InvocationHandler paramInvocationHandler)
{
super(paramInvocationHandler);
}
public final boolean equals(Object paramObject)
{
try
{
return ((Boolean)this.h.invoke(this, m1, new Object[] { paramObject })).booleanValue();
}
catch (Error|RuntimeException localError)
{
throw localError;
}
catch (Throwable localThrowable)
{
throw new UndeclaredThrowableException(localThrowable);
}
}
public final String SayGoodBye()
{
try
{
return (String)this.h.invoke(this, m3, null);
}
catch (Error|RuntimeException localError)
{
throw localError;
}
catch (Throwable localThrowable)
{
throw new UndeclaredThrowableException(localThrowable);
}
}
public final String SayHello(String paramString)
{
try
{
return (String)this.h.invoke(this, m4, new Object[] { paramString });
}
catch (Error|RuntimeException localError)
{
throw localError;
}
catch (Throwable localThrowable)
{
throw new UndeclaredThrowableException(localThrowable);
}
}
public final String toString()
{
try
{
return (String)this.h.invoke(this, m2, null);
}
catch (Error|RuntimeException localError)
{
throw localError;
}
catch (Throwable localThrowable)
{
throw new UndeclaredThrowableException(localThrowable);
}
}
public final int hashCode()
{
try
{
return ((Integer)this.h.invoke(this, m0, null)).intValue();
}
catch (Error|RuntimeException localError)
{
throw localError;
}
catch (Throwable localThrowable)
{
throw new UndeclaredThrowableException(localThrowable);
}
}
static
{
try
{
m1 = Class.forName("java.lang.Object").getMethod("equals", new Class[] { Class.forName("java.lang.Object") });
m3 = Class.forName("jiankunking.Subject").getMethod("SayGoodBye", new Class[0]);
m4 = Class.forName("jiankunking.Subject").getMethod("SayHello", new Class[] { Class.forName("java.lang.String") });
m2 = Class.forName("java.lang.Object").getMethod("toString", new Class[0]);
m0 = Class.forName("java.lang.Object").getMethod("hashCode", new Class[0]);
return;
}
catch (NoSuchMethodException localNoSuchMethodException)
{
throw new NoSuchMethodError(localNoSuchMethodException.getMessage());
}
catch (ClassNotFoundException localClassNotFoundException)
{
throw new NoClassDefFoundError(localClassNotFoundException.getMessage());
}
}
}
参考：Java JDK 动态代理（AOP）使用及实现原理分析
