前言
事件的起因是微服务A通过feign调用微服务B的某个接口，报了形如下的异样
feign.FeignException$NotFound: [404] during [GET] to [http://feign-provider/test/async] [AyncTestServiceClient#testAsync()]: [{"timestamp":"2022-05-28T01:16:36.283+0000","status":404,"error":"Not Found","message":"No message available","path":"/test/async"}]负责微服务A的工程师小张就找到负责提供该接口的工程师小李，问小李是不是改变了接口，小李一脸无辜说他最近没对这个接口做任何改变，不过小李还是说道他排查一下。
排查过程
小李排查的过程如下，他先通过swagger查看他提供给A服务接口是否存在，他一查发现他在swagger上看不到他提供给A服务的接口。于是他狐疑是不是有人动了他的代码，他就去查找最近的git提交记录，发现没人动他的代码，因为我的项目还没公布，都在测试阶段，他就依据我的项目集成的git-commit-id-maven-plugin插件定位到测试目前公布具体是哪个版本。（ps：对
git-commit-id-maven-plugin感兴趣的敌人，能够查看之前的文章聊聊如何验证线上的版本是合乎预期的版本）。而后他将该版本的代码下到本地进行调试，他发现代码中提供给A的接口还在，target下的class也有提供给A的接口class，但诡异的是swagger就是没显示他提供进来的接口，他一度认为是swagger出了问题，于是他用postman间接申请他提供A的接口，发现报了404。而后他就叫负责同个微服务B的共事小王，也帮忙试一下，发现后果就是404。前面没招，小李就去求助他们我的项目资深共事小林。
小林的排查思路如下，他先走查一下小李的接口代码，发现他提供的接口实现层的办法上加了一个@Async，示例形如下
@RestController@RequestMapping(AsyncTestService.INTER_NAME)public class AsyncTestServiceImpl implements AsyncTestService{ @GetMapping("async") @Override public String testAsync() { System.out.println("testAsync start...."); this.doAsynBiz(); System.out.println("testAsync end...."); return "hello async"; } @Async public void doAsynBiz(){ System.out.println("doAsynBiz....."); } }小林凭多年的教训直觉通知小李说，应该是@Async引起。小李很斩钉截铁的说不可能啊，他@Async很早就加了，之前接口都能够拜访的，小林一看小李说得那么必定，他也不好打击小李。于是他接下来做了如下操作，先在我的项目中yml配置如下参数，开启springweb日志
logging: level: org.springframework.web: trace而后在我的项目中加了形如下代码，来跟踪接口bean的类型
for (String beanDefinitionName : applicationContext.getBeanDefinitionNames()) { if(beanDefinitionName.toLowerCase().startsWith("AsyncTestService".toLowerCase())){ System.err.println(beanDefinitionName + "=" + applicationContext.getBean(beanDefinitionName).getClass()); } }启动控制台，看日志形如下
c.d.f.c.ConfigController: {GET /config/test}: test()09:15:04 [main] TRACE o.s.w.s.m.m.a.RequestMappingHandlerMapping - c.d.f.c.ConfigController: {GET /config/test}: test()2022-05-28 09:15:04.564 TRACE 10120 --- [ main] s.w.s.m.m.a.RequestMappingHandlerMapping : c.d.f.i.UserServiceImpl: {GET /user/{id}}: getUserById(Long)09:15:04 [main] TRACE o.s.w.s.m.m.a.RequestMappingHandlerMapping - c.d.f.i.UserServiceImpl: {GET /user/{id}}: getUserById(Long)2022-05-28 09:15:04.577 TRACE 10120 --- [ main] s.w.s.m.m.a.RequestMappingHandlerMapping : s.d.s.w.ApiResourceController: { /swagger-resources/configuration/ui}: uiConfiguration() { /swagger-resources}: swaggerResources() { /swagger-resources/configuration/security}: securityConfiguration()09:15:04 [main] TRACE o.s.w.s.m.m.a.RequestMappingHandlerMapping - s.d.s.w.ApiResourceController: { /swagger-resources/configuration/ui}: uiConfiguration() { /swagger-resources}: swaggerResources() { /swagger-resources/configuration/security}: securityConfiguration()2022-05-28 09:15:04.590 TRACE 10120 --- [ main] s.w.s.m.m.a.RequestMappingHandlerMapping : o.s.b.a.w.s.e.BasicErrorController: { /error}: error(HttpServletRequest) { /error, produces [text/html]}: errorHtml(HttpServletRequest,HttpServletResponse)09:15:04 [main] TRACE o.s.w.s.m.m.a.RequestMappingHandlerMapping - o.s.b.a.w.s.e.BasicErrorController: { /error}: error(HttpServletRequest) { /error, produces [text/html]}: errorHtml(HttpServletRequest,HttpServletResponse)发现的确没打印出相干requestMapping映射信息，这能够阐明一点就是小李那个接口没有绑定到springmvc映射，也就是呈现404的起因。接着察看控制台打印的bean，内容形如下
asyncTestServiceImpl=class com.sun.proxy.$Proxy127这很显著这个接口bean曾经被jdk动静代理给替换。小李看到控制台打印的信息，若有所思，而后说，我把@Async去掉试下。小李把@Async去掉后，再察看下控制台
2022-05-28 10:09:40.814 TRACE 13028 --- [ main] s.w.s.m.m.a.RequestMappingHandlerMapping : c.d.f.c.AsyncTestServiceImpl: {GET /test/async}: testAsync()10:09:40 [main] TRACE o.s.w.s.m.m.a.RequestMappingHandlerMapping - c.d.f.c.AsyncTestServiceImpl: {GET /test/async}: testAsync()2022-05-28 10:09:40.817 TRACE 13028 --- [ main] s.w.s.m.m.a.RequestMappingHandlerMapping : c.d.f.c.ConfigController: {GET /config/test}: test()10:09:40 [main] TRACE o.s.w.s.m.m.a.RequestMappingHandlerMapping - c.d.f.c.ConfigController: {GET /config/test}: test()2022-05-28 10:09:40.820 TRACE 13028 --- [ main] s.w.s.m.m.a.RequestMappingHandlerMapping : c.d.f.i.UserServiceImpl: {GET /user/{id}}: getUserById(Long)asyncTestServiceImpl=class com.demo.feign.controller.AsyncTestServiceImpl通过控制台能够发现，此时接口曾经绑定到springmvc映射，而且打印出bean类型是实在对象bean。小李看到这个景象，也百思不得其解，他说道他之前的确是加了@Async，接口也能失常拜访。于是小林就问一句，你确定你加了@Async，异步失效了吗，小李说开启spring异步，不都是加@Async吗。小林又问了一句，你在我的项目中开启异步，除了加@Async，还有做什么解决吗，小李说没了，他之前在我的项目应用异步就都是加了@Async，也能用了好好的，小林一听，基本上晓得为什么小李之前@Async，接口还能失常拜访了，小林为了验证想法，就问同负责该项目标小王，说你最近有加什么异步操作吗，小王说有，小林进一步问，你是怎么做的，小王说，他先加@EnabledAsyn，开启异步，而后在业务逻辑层上的办法上加@Async注解。小李一听，说原来应用@Async还要配合@EnabledAsyn啊，他之前都不晓得
接着小李说那在controller是不是就不能应用@Async注解了？，小林说最好是把加@Async的逻辑挪到service层去解决，不过也不是controller就不能应用@Async注解了，接着小林为了验证这个想法，他把原来实现的接口类去掉，形如下
@RestController@RequestMapping(AsyncTestService.INTER_NAME)public class AsyncTestServiceImpl{ @GetMapping("async") public String testAsync() { System.out.println(Thread.currentThread().toString() + "-----testAsync start...."); this.doAsynBiz(); System.out.println(Thread.currentThread().toString() + "-----testAsync end...."); return "hello async"; } @Async public void doAsynBiz(){ System.out.println(Thread.currentThread().toString() + "-----doAsynBiz....."); } }启动后，查看控制台
2022-05-28 10:41:31.624 TRACE 5068 --- [ main] s.w.s.m.m.a.RequestMappingHandlerMapping : c.d.f.c.AsyncTestServiceImpl: {GET /test/async}: testAsync()10:41:31 [main] TRACE o.s.w.s.m.m.a.RequestMappingHandlerMapping - c.d.f.c.AsyncTestServiceImpl: {GET /test/async}: testAsync()2022-05-28 10:41:31.627 TRACE 5068 --- [ main] s.w.s.m.m.a.RequestMappingHandlerMapping : c.d.f.c.ConfigController: {GET /config/test}: test()10:41:31 [main] TRACE o.s.w.s.m.m.a.RequestMappingHandlerMapping - 此时bean的类型如下
asyncTestServiceImpl=class com.demo.feign.controller.AsyncTestServiceImpl$$EnhancerBySpringCGLIB$$a285a21c拜访接口，打印内容如下
Thread[http-nio-8080-exec-1,5,main]-----testAsync start....Thread[http-nio-8080-exec-1,5,main]-----doAsynBiz.....Thread[http-nio-8080-exec-1,5,main]-----testAsync end....从控制台能够发现，都是http-nio-8080-exec-1线程触发，阐明异步没失效，即@Async生效。前面对controller做了如下革新
@RestController@RequestMapping(AsyncTestService.INTER_NAME)public class AsyncTestServiceImpl{ @Autowired private ObjectProvider<AsyncTestServiceImpl> asyncTestServices; @GetMapping("async") public String testAsync() { System.out.println(Thread.currentThread().toString() + "-----testAsync start...."); asyncTestServices.getIfAvailable().doAsynBiz(); System.out.println(Thread.currentThread().toString() + "-----testAsync end...."); return "hello async"; } @Async public void doAsynBiz(){ System.out.println(Thread.currentThread().toString() + "-----doAsynBiz....."); } }拜访接口，打印内容如下
Thread[http-nio-8080-exec-2,5,main]-----testAsync start....Thread[http-nio-8080-exec-2,5,main]-----testAsync end....Thread[task-1,5,main]-----doAsynBiz.....这阐明在controller其实也是能够用@Async，只是要额定做解决。所以倡议是把@Async从controller中抽离进来，在新类中进行解决，示例如下
@Servicepublic class AysncService { @Async public void doAsynBiz(){ System.out.println(Thread.currentThread().getName() + "-----doAsynBiz....."); }}@RestController@RequestMapping(AsyncTestService.INTER_NAME)@RequiredArgsConstructorpublic class AsyncTestServiceImpl implements AsyncTestService { private final AysncService aysncService; @Override public String testAsync() { System.out.println(Thread.currentThread().getName() + "-----testAsync start...."); aysncService.doAsynBiz(); System.out.println(Thread.currentThread().getName() + "-----testAsync end...."); return "hello async"; }}拜访接口，打印内容
http-nio-8080-exec-1-----testAsync start....http-nio-8080-exec-1-----testAsync end....task-1-----doAsynBiz.....阐明异步失效
排查后果剖析
1、接口404
从mvc日志
2022-05-28 10:59:50.394 TRACE 14152 --- [ main] s.w.s.m.m.a.RequestMappingHandlerMapping : c.d.f.c.AsyncTestServiceImpl: {GET /test/async}: testAsync()10:59:50 [main] TRACE o.s.w.s.m.m.a.RequestMappingHandlerMapping - c.d.f.c.AsyncTestServiceImpl: {GET /test/async}: testAsync()2022-05-28 10:59:50.397 TRACE 14152 --- [ main] s.w.s.m.m.a.RequestMappingHandlerMapping : 咱们能够晓得，controller映射解决是在RequestMappingHandlerMapping 这个类中，但具体是哪个办法进行解决呢，咱们能够通过日志打印的信息，进行倒推，也能够基于spring的个性加断点调试，比方通过afterPropertiesSet这一启动扩大点调试起，就会发现RequestMappingHandlerMapping的映射解决是在
protected void initHandlerMethods() { for (String beanName : getCandidateBeanNames()) { if (!beanName.startsWith(SCOPED_TARGET_NAME_PREFIX)) { processCandidateBean(beanName); } } handlerMethodsInitialized(getHandlerMethods()); }进行解决，具体是通过processCandidateBean进行解决
protected void processCandidateBean(String beanName) { Class<?> beanType = null; try { beanType = obtainApplicationContext().getType(beanName); } catch (Throwable ex) { // An unresolvable bean type, probably from a lazy bean - let's ignore it. if (logger.isTraceEnabled()) { logger.trace("Could not resolve type for bean '" + beanName + "'", ex); } } if (beanType != null && isHandler(beanType)) { detectHandlerMethods(beanName); } }最终是通过detectHandlerMethods进行解决
protected void detectHandlerMethods(Object handler) { Class<?> handlerType = (handler instanceof String ? obtainApplicationContext().getType((String) handler) : handler.getClass()); if (handlerType != null) { Class<?> userType = ClassUtils.getUserClass(handlerType); Map<Method, T> methods = MethodIntrospector.selectMethods(userType, (MethodIntrospector.MetadataLookup<T>) method -> { try { return getMappingForMethod(method, userType); } catch (Throwable ex) { throw new IllegalStateException("Invalid mapping on handler class [" + userType.getName() + "]: " + method, ex); } }); if (logger.isTraceEnabled()) { logger.trace(formatMappings(userType, methods)); } methods.forEach((method, mapping) -> { Method invocableMethod = AopUtils.selectInvocableMethod(method, userType); registerHandlerMethod(handler, invocableMethod, mapping); }); } }这个外面就是做了理论注册。而执行detectHandlerMethods的前提是
beanType != null && isHandler(beanType) @Override protected boolean isHandler(Class<?> beanType) { return (AnnotatedElementUtils.hasAnnotation(beanType, Controller.class) || AnnotatedElementUtils.hasAnnotation(beanType, RequestMapping.class)); }即只有加了@Controller或者@RequestMapping的类会进行解决，而@RestController为啥也解决，点击
@RestController发现
@Target(ElementType.TYPE)@Retention(RetentionPolicy.RUNTIME)@Documented@Controller@ResponseBodypublic @interface RestController {他实质就是@Controller。但咱们通过反射查找注解，失常只会查找一层，比方
AsynTestController.class.getAnnotation(RestController.class)他找到@RestController这一层，而不会找持续再找@RestController外面的@Controller，而AnnotatedElementUtils.hasAnnotation，这个注解办法就不一样，他是能够找到合并注解，即便是应用
@RestController，他还会持续找到外面的@Controller。因而这个办法对于找复合型注解很有用
当咱们应用jdk动静代理时，因为父类上没加@Controller或者@RequestMapping，因而他不会被mvc进行映射解决，导致404。而应用cglib时，因为他是作为子类继承了指标类，因而他会继承指标类上的注解，因而当为cglib代理时，他会失常被mvc进行映射解决
2、为何controller外面加了@Asyn异步就生效了
这是因为加了@Async后，controller变成代理了，而当要异步解决办法，用this时，他应用的是指标对象，而非代理对象。这跟当初面试事务为啥事务生效的八股文根本是一个套路
总结
本文次要讲@Async导致controller 404，同时也使@Async生效的起因。解决的举荐办法就是将@Async抽离出controller，新建一个service类进行解决。