Java 動態代理原理圖解 (附：2種實現方式詳細對比)

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
 
/**
* JDK Proxy 相關範例
*/
public class ProxyExample {
static interface Car {
void running();
}
 
static class Bus implements Car {
@Override
public void running() {
System.out.println("The bus is running.");
}
}
 
static class Taxi implements Car {
@Override
public void running() {
System.out.println("The taxi is running.");
}
}
 
/**
* JDK Proxy
*/
static class JDKProxy implements InvocationHandler {
private Object target; // 代理物件
 
// 獲取到代理物件
public Object getInstance(Object target) {
this.target = target;
// 取得代理物件
return Proxy.newProxyInstance(target.getClass().getClassLoader(),
target.getClass().getInterfaces(), this);
}
 
/**
* 執行代理方法
* @param proxy 代理物件
* @param method 代理方法
* @param args 方法的引數
* @return
* @throws InvocationTargetException
* @throws IllegalAccessException
*/
@Override
public Object invoke(Object proxy, Method method, Object[] args)
throws InvocationTargetException, IllegalAccessException {
System.out.println("動態代理之前的業務處理.");
Object result = method.invoke(target, args); // 執行呼叫方法（此方法執行前後，可以進行相關業務處理）
return result;
}
}
 
public static void main(String[] args) {
// 執行 JDK Proxy
JDKProxy jdkProxy = new JDKProxy();
Car carInstance = (Car) jdkProxy.getInstance(new Taxi());
carInstance.running();

 The taxi is running.

public interface InvocationHandler {
public Object invoke(Object proxy, Method method, Object[] args)
throws Throwable;
}

<dependency>
<groupId>cglib</groupId>
<artifactId>cglib</artifactId>
<version>3.3.0</version>
</dependency>

package com.mikechen.proxydemo;
 
import net.sf.cglib.proxy.Enhancer;
import net.sf.cglib.proxy.MethodInterceptor;
import net.sf.cglib.proxy.MethodProxy;
 
import java.lang.reflect.Method;
 
public class CGLibExample {
 
static class Car {
public void running() {
System.out.println("The car is running.");
}
}
 
/**
* CGLib 代理類
*/
static class CGLibProxy implements MethodInterceptor {
private Object target; // 代理物件
 
public Object getInstance(Object target) {
this.target = target;
Enhancer enhancer = new Enhancer();
// 設定父類別為範例類
enhancer.setSuperclass(this.target.getClass());
// 回撥方法
enhancer.setCallback(this);
// 建立代理物件
return enhancer.create();
}
 
@Override
public Object intercept(Object o, Method method,
Object[] objects, MethodProxy methodProxy) throws Throwable {
System.out.println("方法呼叫前業務處理.");
Object result = methodProxy.invokeSuper(o, objects); // 執行方法呼叫
return result;
}
}
 
// 執行 CGLib 的方法呼叫
public static void main(String[] args) {
// 建立 CGLib 代理類
CGLibProxy proxy = new CGLibProxy();
// 初始化代理物件
Car car = (Car) proxy.getInstance(new Car());
// 執行方法
car.running();

The car is running.