背景
静态代理的弊端是对于被代理类的方法要逐个实现，比较繁琐。此外在被代理对象方法变更时也要对应的变更，维护也不方便。动态代理可以方便的解决该问题。
实现步骤
- 声明接口: 为了方便使用JDK的UpdateCheckListener接口
- 接口实现类
import com.oracle.deploy.update.UpdateCheckListener;
/**
* 接口实现类
* @author lixiaowen
* @date 2019/2/11
*/
public class UpdateCheckListenerImpl implements UpdateCheckListener {
@Override
public void updateCheckStateChanged(int i) {
System.out.println("original i = " + i);
}
}
- JDK代理类实现
import com.oracle.deploy.update.UpdateCheckListener;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
/**
* jdk 动态代理实现{@link UpdateCheckListener}
* @author lixiaowen
* @date 2019/2/11
*/
public class UpdateCheckListenerJdkProxy implements InvocationHandler {
//被代理的对象
private UpdateCheckListener source;
public UpdateCheckListenerJdkProxy(UpdateCheckListener source) {
this.source = source;
}
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
System.out.println("JDK实现代理..." + method);
return method.invoke(source, args);
}
}
- 客户端测试
public static void main(String[] args) throws IllegalAccessException, InstantiationException {
//代理类写入文件
System.getProperties().setProperty("sun.misc.ProxyGenerator.saveGeneratedFiles","true");
UpdateCheckListenerJdkProxy jdkProxy = new UpdateCheckListenerJdkProxy(UpdateCheckListenerImpl.class.newInstance());
UpdateCheckListener proxy = (UpdateCheckListener) Proxy.newProxyInstance(UpdateCheckListener.class.getClassLoader(),
new Class[]{UpdateCheckListener.class},
jdkProxy);
proxy.updateCheckStateChanged(666);
}
原理
生成的UpdateCheckListenerImpl代理类class文件
package com.sun.proxy;
import com.oracle.deploy.update.UpdateCheckListener;
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 UpdateCheckListener {
private static Method m1;
private static Method m2;
private static Method m3;
private static Method m0;
public $Proxy0(InvocationHandler var1) throws {
super(var1);
}
public final boolean equals(Object var1) throws {
try {
return (Boolean)super.h.invoke(this, m1, new Object[]{var1});
} catch (RuntimeException | Error var3) {
throw var3;
} catch (Throwable var4) {
throw new UndeclaredThrowableException(var4);
}
}
public final String toString() throws {
try {
return (String)super.h.invoke(this, m2, (Object[])null);
} catch (RuntimeException | Error var2) {
throw var2;
} catch (Throwable var3) {
throw new UndeclaredThrowableException(var3);
}
}
public final void updateCheckStateChanged(int var1) throws {
try {
super.h.invoke(this, m3, new Object[]{var1});
} catch (RuntimeException | Error var3) {
throw var3;
} catch (Throwable var4) {
throw new UndeclaredThrowableException(var4);
}
}
public final int hashCode() throws {
try {
return (Integer)super.h.invoke(this, m0, (Object[])null);
} catch (RuntimeException | Error var2) {
throw var2;
} catch (Throwable var3) {
throw new UndeclaredThrowableException(var3);
}
}
static {
try {
m1 = Class.forName("java.lang.Object").getMethod("equals", Class.forName("java.lang.Object"));
m2 = Class.forName("java.lang.Object").getMethod("toString");
m3 = Class.forName("com.oracle.deploy.update.UpdateCheckListener").getMethod("updateCheckStateChanged", Integer.TYPE);
m0 = Class.forName("java.lang.Object").getMethod("hashCode");
} catch (NoSuchMethodException var2) {
throw new NoSuchMethodError(var2.getMessage());
} catch (ClassNotFoundException var3) {
throw new NoClassDefFoundError(var3.getMessage());
}
}
}
从代码中可以看出，JDK生成了新的类$Proxy0,，该类实现了UpdateCheckListener接口， 并且在构造器的时候传递InvocationHandler对象，并赋值给super.h。
updateCheckStateChanged方法调用的时候，运行期间通过super.h调用invoker方法实现的。
super.h是构造器的var1传递过来的，该对象是通过反射生成实例的时候传递的，也就是jdkProxy对象。
- $Proxy0的class文件生成过程
Proxy.newProxyInstance() -> Prxoy.getProxyClass0() -> Proxy.proxyClassCache -> Proxy.ProxyClassFactory.apply() ->ProxyGenerator.generateProxyClass()
