前世今生

它的本质就是 JDK 的动态代理。首先先来复习一下动态代理我贴了一段最常见的 JDK 动态代理的代码

//服务员的接口public interface Waiter {  void serve();}//服务员的实现public class WaiterImpl implements Waiter {  @Override  public void serve() {    System.out.println("服务中...");  }}//需要代理的对象处理器class WaitInvocationHandler implements InvocationHandler {  private Waiter waiter;  public WaitInvocationHandler(Waiter waiter1) {    waiter = waiter1;  }  @Override  public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {    System.out.println("你好");    Object invoke = method.invoke(waiter, args);    System.out.println("再见");    return invoke;  }}public class App {  //普通的实现  @Test  public void fun() {    Waiter waiter = new WaiterImpl();    waiter.serve();  }  @Test  public void fun1() {    Waiter a = new WaiterImpl();    ClassLoader classLoader = getClass().getClassLoader();    Class[] classes = {Waiter.class};    //生成代理对象    Waiter waiterproxy = (Waiter) Proxy.newProxyInstance(classLoader, classes, new WaitInvocationHandler(a));    waiterproxy.serve();  }}

拦截器

V1

我现在要在函数执行前后记录日志操作，考虑需要在代理方法那里定义个拦截器的接口，如下代码所示

//拦截器 V1 版本public interface MyInterceptorV1 {  void interceptor();}//代理对象变成这个public class TargetProxyV1 implements InvocationHandler {  private Target target;  private MyInterceptorV1 myInterceptor;  public TargetProxyV1(Target target, MyInterceptorV1 myInterceptor) {    this.target = target;    this.myInterceptor = myInterceptor;  }  @Override  public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {    myInterceptor.interceptor();    return method.invoke(target, args);  }}

这是最简单的版本，但是我们很多时候需要拦截参数等根据参数判断拦不拦截等，代码更新如下

public interface MyInterceptorV1 {  void interceptor(Method method, Object[] args);}@Overridepublic Object invoke(Object proxy, Method method, Object[] args) throws Throwable {  myInterceptor.interceptor(method, args);  return method.invoke(target, args);}

V2

似乎上面的方案很完美

废话肯定不完美，不然怎么会有这段

没错，第二段代码并不是很优雅，有方法参数重复，可以考虑将三者抽出来，直接在拦截器的实现里写上 method.invoke(target, args); ，如下代码所示

@Getter@Setter@AllArgsConstructorpublic class MyInvocation {  private Object target;  private Method method;  private Object[] args;  public Object proceed() throws InvocationTargetException, IllegalAccessException {    return method.invoke(target, args);  }}//没错这就是 V2 版本public interface MyInterceptorV2 {  Object interceptor(MyInvocation invocation) throws Throwable;}