Spring如何基于Proxy及cglib实现动态代理

spring中提供了两种动态代理的方式，分别是Java Proxy以及cglib

JavaProxy只能代理接口，而cglib是通过继承的方式，实现对类的代理

添加一个接口以及对应的实现类

public interface HelloInterface {
  void sayHello();
}

public class HelloInterfaceImpl implements HelloInterface {
  @Override
  public void sayHello() {
    System.out.println("hello");
  }
}

JavaProxy通过实现InvocationHandler实现代理

public class CustomInvocationHandler implements InvocationHandler {
  private HelloInterface helloInterface;

  public CustomInvocationHandler(HelloInterface helloInterface) {
    this.helloInterface = helloInterface;
  }

  @Override
  public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    System.out.println("before hello for proxy");
    Object result = method.invoke(helloInterface, args);
    System.out.println("after hello for proxy");
    return result;
  }
}

而cglib实现MethodInterceptor进行方法上的代理

public class CustomMethodInterceptor implements MethodInterceptor {
  @Override
  public Object intercept(Object o, Method method, Object[] objects, MethodProxy methodProxy) throws Throwable {
    System.out.println("before hello for cglib");
    Object result = methodProxy.invokeSuper(o, objects);
    System.out.println("after hello for cglib");
    return result;
  }

}

分别实现调用代码

public static void main(String[] args) {
    Enhancer enhancer = new Enhancer();
    enhancer.setSuperclass(HelloInterfaceImpl.class);
    enhancer.setCallback(new CustomMethodInterceptor());
    HelloInterface target = (HelloInterface) enhancer.create();
    target.sayHello();

    CustomInvocationHandler invocationHandler = new CustomInvocationHandler(new HelloInterfaceImpl());
    HelloInterface target2 = (HelloInterface) Proxy.newProxyInstance(Demo.class.getClassLoader(), new Class[]{HelloInterface.class}, invocationHandler);
    target2.sayHello();
  }

可以看到对于的代理信息输出

before hello for cglib
hello
after hello for cglib
before hello for proxy
hello
after hello for proxy

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