Spring Async使用以及ThreadPoolTaskScheduler not initialized問題分析

引言

在系統中，對於耗時比較多的操作，一般都會使用異步操作，或者單獨開一個線程進行處理。在Spring中，直接內置了@Async幫助大家一步到位，簡化使用，本文分析其中的一個問題。

代碼

代碼最直觀，直接上代碼：

 @Slf4j
@Configuration
@EnableAsync
public class AsyncConfig implements AsyncConfigurer {
    @Override
    public Executor getAsyncExecutor() {
        log.info("boot the async executor....");
        ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
        return executor;
    }
}

上述代碼， @EnableAsync啓動@Async的使用，並使用@Configuration註冊到IoC容器中。
這裏的Executor是定義的一個線程池，用於執行@Async的方法

對於單個方法的示例如下：

@Service
public class AsyncService {
    @Async
    public Future<String> asyncMethodWithReturnType()  {
         //邏輯操作
        try {
             Thread.sleep(5000);
             return new AsyncResult<String>("Async Message");
        } catch (InterruptedException e) {
              //Exception Handling
        }
        return new AsyncResult<>("Exception Occurs");
    }
}

方法使用@Async來修飾，表示將異步執行。其結果用Future方式修飾，表示需要異步返回的結果。
在Web層的Controller代碼如下：

@RestController
@Slf4j
public class Controller {
    @Autowired
    private AsyncService asyncService;

    @GetMapping("/async")
    public String handleAsync() throws ExecutionException, InterruptedException {
        Future<String> resultMsg =  this.asyncService.asyncMethodWithReturnType();
        String mesg = Objects.nonNull(resultMsg) ? resultMsg.get() : "No message";
        return mesg;
    }
}

Web請求中調用asyc方法

啓動中的問題

在系統啓動之後，碰到了如下問題：


java.lang.IllegalStateException: ThreadPoolTaskExecutor not initialized
	at org.springframework.util.Assert.state(Assert.java:73) ~[spring-core-5.2.1.RELEASE.jar:5.2.1.RELEASE]
	at org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor.getThreadPoolExecutor(ThreadPoolTaskExecutor.java:281) ~[spring-context-5.2.1.RELEASE.jar:5.2.1.RELEASE]
	at org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor.submit(ThreadPoolTaskExecutor.java:339) ~[spring-context-5.2.1.RELEASE.jar:5.2.1.RELEASE]
	at org.springframework.aop.interceptor.AsyncExecutionAspectSupport.doSubmit(AsyncExecutionAspectSupport.java:287) ~[spring-aop-5.2.1.RELEASE.jar:5.2.1.RELEASE]
	at org.springframework.aop.interceptor.AsyncExecutionInterceptor.invoke(AsyncExecutionInterceptor.java:129) ~[spring-aop-5.2.1.RELEASE.jar:5.2.1.RELEASE]
	at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.2.1.RELEASE.jar:5.2.1.RELEASE]
	at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.proceed(CglibAopProxy.java:747) ~[spring-aop-5.2.1.RELEASE.jar:5.2.1.RELEASE]
	at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:689) ~[spring-aop-5.2.1.RELEASE.jar:5.2.1.RELEASE]
	at org.spb.data.service.AsyncService$$EnhancerBySpringCGLIB$$3878556.asyncMethodWithReturnType(<generated>) ~[classes/:na]
	at org.spb.data.Controller.handleAsync(Controller.java:21) ~[classes/:na]
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_192]
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_192]
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_192]
	at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_192]
	at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:190) ~[spring-web-5.2.1.RELEASE.jar:5.2.1.RELEASE]
	at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:138) ~[spring-web-5.2.1.RELEASE.jar:5.2.1.RELEASE]
	at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:106) ~[spring-webmvc-5.2.1.RELEASE.jar:5.2.1.RELEASE]
	at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:888) ~[spring-webmvc-5.2.1.RELEASE.jar:5.2.1.RELEASE]
	at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:793) ~[spring-webmvc-5.2.1.RELEASE.jar:5.2.1.RELEASE]
	at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87) ~[spring-webmvc-5.2.1.RELEASE.jar:5.2.1.RELEASE]
	at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1040) ~[spring-webmvc-5.2.1.RELEASE.jar:5.2.1.RELEASE]
	at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:943) ~[spring-webmvc-5.2.1.RELEASE.jar:5.2.1.RELEASE]
	at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006) ~[spring-webmvc-5.2.1.RELEASE.jar:5.2.1.RELEASE]
	at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:898) ~[spring-webmvc-5.2.1.RELEASE.jar:5.2.1.RELEASE]
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:634) ~[tomcat-embed-core-9.0.27.jar:9.0.27]
	at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883) ~[spring-webmvc-5.2.1.RELEASE.jar:5.2.1.RELEASE]
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:741) ~[tomcat-embed-core-9.0.27.jar:9.0.27]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) ~[tomcat-embed-core-9.0.27.jar:9.0.27]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.27.jar:9.0.27]
	at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53) ~[tomcat-embed-websocket-9.0.27.jar:9.0.27]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.27.jar:9.0.27]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.27.jar:9.0.27]
	at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201) ~[spring-web-5.2.1.RELEASE.jar:5.2.1.RELEASE]
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.2.1.RELEASE.jar:5.2.1.RELEASE]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.27.jar:9.0.27]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.27.jar:9.0.27]
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202) ~[tomcat-embed-core-9.0.27.jar:9.0.27]
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) [tomcat-embed-core-9.0.27.jar:9.0.27]
	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:526) [tomcat-embed-core-9.0.27.jar:9.0.27]
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139) [tomcat-embed-core-9.0.27.jar:9.0.27]
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) [tomcat-embed-core-9.0.27.jar:9.0.27]
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74) [tomcat-embed-core-9.0.27.jar:9.0.27]
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343) [tomcat-embed-core-9.0.27.jar:9.0.27]
	at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:408) [tomcat-embed-core-9.0.27.jar:9.0.27]
	at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66) [tomcat-embed-core-9.0.27.jar:9.0.27]
	at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:861) [tomcat-embed-core-9.0.27.jar:9.0.27]
	at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1579) [tomcat-embed-core-9.0.27.jar:9.0.27]
	at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) [tomcat-embed-core-9.0.27.jar:9.0.27]
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [na:1.8.0_192]
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [na:1.8.0_192]
	at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-embed-core-9.0.27.jar:9.0.27]
	at java.lang.Thread.run(Thread.java:748) [na:1.8.0_192]

出錯了，核心錯誤信息如下：

java.lang.IllegalStateException: ThreadPoolTaskExecutor not initialized

明明是聲明瞭的，爲什麼初始化失敗？
原來是需要顯示調用： initialize()方法。具體代碼如下：

@Slf4j
@Configuration
@EnableAsync
public class AsyncConfig implements AsyncConfigurer {
    @Override
    public Executor getAsyncExecutor() {
        log.info("boot the async executor....");
        ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
        executor.initialize();

        return executor;
    }
}

即可順利啓動成功，且執行成功了。

日誌分析

在上述日誌可知，在系統啓動成功後，在真正應用調用的時候，才進行Web Dispatcher的初始化，然後初始化ExecutorService的線程池，即@Async的線程池。

從系統設計的角度，從設計的角度來看，Spring框架將非核心與應用層分離，優先啓動系統核心，應用層推遲到核心啓動之後，加速系統框架的啓動過程。在初次用到的時候，在初始化所需實例。

Async的限制

在使用上有以下兩個限制：方法必須爲public和@Async方法和調用方不能在同一個類中定義，底層的原因是動態代理機制在同一個類方法之間的調用時，代理會失效。對於有返回結果的方法，需要使用Future類型，用於異步操作返回的結果。

總結

@Async簡單易用，值得推薦。

參考文檔

Spring Async

Spring Async使用以及ThreadPoolTaskScheduler not initialized問題分析

引言

代碼

啓動中的問題

日誌分析

Async的限制

總結

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