Spring Retry实现原理

在前面这篇博客中介绍了Spring Retry的使用，本文通过一个简单的例子演示Spring Retry的实现原理，例子中定义的注解只包含重试次数属性，实际上Spring Retry中注解可设置属性要多的多，单纯为了讲解原理，所以弄简单点，关于Spring Retry可查阅相关文档、博客。

注解定义

package retry.annotation;import java.lang.annotation.*;/** * Created by Jack.wu on 2016/9/30. */@Target(ElementType.METHOD)@Retention(RetentionPolicy.RUNTIME)@Documentedpublic @interface Retryable {    int maxAttemps() default 0;}
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代理实现

以Cglib作为代理工具，先来写个Callback实现，这也是重试的实现的核心逻辑

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;    }}
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然后是写个代理类，使用AnnotationAwareRetryOperationsInterceptor作为拦截器

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();    }}
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测试

通过一个用户相关的业务方法来测试上面的代码

接口定义：

package facade;/** * Created by Jack.wu on 2016/9/26. */public interface UserFacade {    void add() throws Exception;    void query() throws Exception;}
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接口实现：

package facade.impl;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();    }}
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测试：

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    }}
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add方法不添加重试注解，程序异常结束，query方法添加重试注解，设置重试3次，运行效果如下 

http://blog.csdn.net/u014513883/article/details/52712870