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)
@Documented
public @interface Retryable {
int maxAttemps() default 0;
}
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;
}
}
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();
}
}
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;
}
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();
}
}
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
}
}
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
