动态代理的三种实现

第一种方式：JDK

原理：利用反射去调方法，Proxy这个类就是java.lang.reflect包下面的

1. 拿到被代理类的class对象 --target

2. 动态生成一个代理类CLASSA（class com.sun.proxy.$Proxy3），这类实现被代理类的所有接口

3. 获取这个CLASSA的一个参数为InvocationHandler的构造方法

4. 调用这个构造方法创建实例（这个就是代理对象）；参数就是这个代理类WorkerProxy

   大概的意思应该是这样的如下图，反射内容见
   https://blog.youkuaiyun.com/u013523089/article/details/83999137
   

示例：

public class WorkerProxy implements InvocationHandler{

	private Object target;
	
	public WorkerProxy(Object target) {
		// TODO Auto-generated constructor stub
		this.target = target;
	}
	
	@Override
	public Object invoke(Object arg0, Method arg1, Object[] arg2) throws Throwable {
		// TODO Auto-generated method stub
		System.out.println("员工盖房子");
		return arg1.invoke(target, arg2);
	}
	
	
}

测试类

			IBuilder builder1 = (IBuilder) Proxy.newProxyInstance(IBuilder.class.getClassLoader(), 
					new Class[]{IBuilder.class}, 
					new WorkerProxy(new Boss()));
			builder1.buildHouse();

第二种方法，cglib

代理类通过字节码技术创建一个被代理类的子类实例

public class WorkerProxy implements MethodInterceptor{
	private Enhancer enhancer = new Enhancer();
	
	public Object getProxy(Class<?> clazz) {
		//设置需要创建子类的类
		enhancer.setSuperclass(clazz);
		enhancer.setCallback(this);
		//通过字节码技术，动态创建子类实例
		return enhancer.create();
	}

	@Override
	public Object intercept(Object arg0, Method arg1, Object[] arg2, MethodProxy arg3) throws Throwable {
		System.out.println("员工建房子");
		//通过代理，调用父类的方法
		return arg3.invokeSuper(arg0, arg2);
	}

}

测试类

		WorkerProxy worker = new WorkerProxy();
		IBuilder builder = (IBuilder) worker.getProxy(Boss.class);
		builder.buildHouse();

第三种：javassist

javassist.util.proxy
或使用org.apache.ibatis.javassist.util.proxy

public class WorkerProxy1 implements MethodHandler{

	@Override
	public Object invoke(Object arg0, Method arg1, Method arg2, Object[] arg3) throws Throwable {
		// TODO Auto-generated method stub
		System.out.println("PROXY");
		return arg2.invoke(arg0, arg3);
	}

}

测试代码

			ProxyFactory factory = new ProxyFactory();
			factory.setSuperclass(Boss.class);
			Class<?> clazz = factory.createClass();
			IBuilder testDemo = (IBuilder) clazz.newInstance();
			((ProxyObject)testDemo).setHandler(new WorkerProxy1());
			testDemo.buildHouse();