在前面這篇博客中介紹了Spring Retry的使用,本文通過一個簡單的例子演示Spring Retry的實現原理,例子中定義的註解只包含重試次數屬性,實際上Spring Retry中註解可設置屬性要多的多,單純為了講解原理,所以弄簡單點,關於Spring Retry可查閱相關文檔、博客。
註解定義
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;}代理實現
以Cglib作為代理工具,先來寫個Callback實現,這也是重試的實現的核心邏輯
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{ //記錄重試次數private int times = 0; @Override public Object intercept(Object obj, Method method, Object[] args, MethodProxy proxy) throws Throwable { //獲取攔截的方法中的Retryable註解Retryable retryable = method.getAnnotation(Retryable.class); if(retryable == null){ return proxy.invokeSuper(obj,args); }else{ //有Retryable註解,加入異常重試邏輯int maxAttemps = retryable.maxAttemps(); try { return proxy.invokeSuper(obj,args); } catch (Throwable e) { if(times++ == maxAttemps){ System.out.println("已達最大重試次數:" + maxAttemps + ",不再重試!"); }else{ System.out.println("調用" + method.getName() + "方法異常,開始第" + times +"次重試。。。"); //注意這裡不是invokeSuper方法,invokeSuper會退出當前interceptor的處理proxy.invoke(obj,args); } } } return null; }}然後是寫個代理類,使用AnnotationAwareRetryOperationsInterceptor作為攔截器
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(); }}測試
通過一個用戶相關的業務方法來測試上面的代碼
接口定義:
package facade;/** * Created by Jack.wu on 2016/9/26. */public interface UserFacade { void add() throws Exception; void query() throws Exception;}接口實現: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("添加用戶。。。"); throw new RuntimeException(); } @Override @Retryable(maxAttemps = 3) public void query() { System.out.println("查詢用戶。。。"); throw new RuntimeException(); }}測試:
public class Main { public static void main(String[] args) throws Exception{ UserFacadeImpl user = new UserFacadeImpl(); //SpringRetry代理測試SpringRetryProxy springRetryProxy = new SpringRetryProxy(); UserFacade u = (UserFacade)springRetryProxy.newProxyInstance(user); //u.add();//失敗不重試u.query();//失敗重試}} add方法不添加重試註解,程序異常結束,query方法添加重試註解,設置重試3次,運行效果如下
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