Spring Retry实现原理

r囧r小猫 2022-07-16 03:19 81阅读 0赞

在前面[这篇博客][Link 1]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  
![这里写图片描述][format_png]

[Link 1]: http://blog.csdn.net/u014513883/article/details/52371198
[format_png]: /images/20220716/4c54913672c8420babe4aac9e9e1a9c9.png