详解Spring Retry实现原理

package retry.annotation;

import java.lang.annotation.*;

/**
 * Created by Jack.wu on 2016/9/30.
 */
@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Retryable {

  int maxAttemps() default 0;

}

package retry.interceptor;

import net.sf.cglib.proxy.MethodInterceptor;
import net.sf.cglib.proxy.MethodProxy;
import retry.annotation.Retryable;

import java.lang.reflect.Method;

/**
 * Created by Jack.wu on 2016/9/30.
 */
public class AnnotationAwareRetryOperationsInterceptor implements MethodInterceptor{

  //记录重试次数
  private int times = 0;

  @Override
  public Object intercept(Object obj, Method method, Object[] args, MethodProxy proxy) throws Throwable {
    //获取拦截的方法中的Retryable注解
    Retryable retryable = method.getAnnotation(Retryable.class);
    if(retryable == null){
      return proxy.invokeSuper(obj,args);
    }else{ //有Retryable注解，加入异常重试逻辑
      int maxAttemps = retryable.maxAttemps();
      try {
        return proxy.invokeSuper(obj,args);
      } catch (Throwable e) {
        if(times++ == maxAttemps){
          System.out.println("已达最大重试次数：" + maxAttemps + ",不再重试！");
        }else{
          System.out.println("调用" + method.getName() + "方法异常，开始第" + times +"次重试。。。");
          //注意这里不是invokeSuper方法，invokeSuper会退出当前interceptor的处理
          proxy.invoke(obj,args);
        }
      }
    }
    return null;
  }
}

package retry.core;
import net.sf.cglib.proxy.Enhancer;
import retry.interceptor.AnnotationAwareRetryOperationsInterceptor;

/**
 * Created by Jack.wu on 2016/9/30.
 */
public class SpringRetryProxy {

  public Object newProxyInstance(Object target){
    Enhancer enhancer = new Enhancer();
    enhancer.setSuperclass(target.getClass());
    enhancer.setCallback(new AnnotationAwareRetryOperationsInterceptor());
    return enhancer.create();
  }
}

package facade;

/**
 * Created by Jack.wu on 2016/9/26.
 */
public interface UserFacade {

  void add() throws Exception;

  void query() throws Exception;
}

import facade.UserFacade;
import retry.annotation.Retryable;
/**
 * Created by Jack.wu on 2016/9/26.
 */
public class UserFacadeImpl implements UserFacade {
  @Override
  public void add() throws Exception {
    System.out.println("添加用户。。。");
    throw new RuntimeException();
  }

  @Override
  @Retryable(maxAttemps = 3)
  public void query() {
    System.out.println("查询用户。。。");
    throw new RuntimeException();
  }
}

public class Main {

  public static void main(String[] args) throws Exception{
    UserFacadeImpl user = new UserFacadeImpl();
    //SpringRetry代理测试
    SpringRetryProxy springRetryProxy = new SpringRetryProxy();
    UserFacade u = (UserFacade)springRetryProxy.newProxyInstance(user);
    //u.add();//失败不重试
    u.query();//失败重试
  }
}