JavaWeb项目中如果想对某个接口设置重试机制,可用Spring的@Retryable注解实现接口重试。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很多。
一、注解定义
package retry.annotation;
import java.lang.annotation.*;
@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Retryable {
int maxAttemps() default 0;
}
二、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;
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();
}
}
三、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