1、java的大部分接口的方法都是串行執(zhí)行的，但是有些業(yè)務(wù)場景是不需要同步返回結(jié)果的，可以把結(jié)果直接返回，具體業(yè)務(wù)異步執(zhí)行，也有些業(yè)務(wù)接口是需要并行獲取數(shù)據(jù)，最后把數(shù)據(jù)聚合在統(tǒng)一返回給前端。通常我們都是采用多線程的方式來實現(xiàn)上述業(yè)務(wù)功能，但spring 提供更優(yōu)雅的方式來實現(xiàn)上述功能，就是@Async 異步注解，在方法上添加@Async，spring就會借助AOP，異步執(zhí)行方法。

spring boot通過@EnableAsync 注解啟用@Async異步注解實現(xiàn)AsyncConfigurer接口，getAsyncExecutor是默認(rèn)自定義的線程池

/** * 線程池配置（@Async） */@Slf4j@EnableAsync@Configurationpublic class SimpleExecutorConfig implements AsyncConfigurer { /** 線程池維護線程的最少數(shù)量 */ @Value('${executor.corePoolSize}') private Integer corePoolSize; /** 線程池維護線程的最大數(shù)量 */ @Value('${executor.maxPoolSize}') private Integer maxPoolSize; /** 緩沖隊列的大小 */ @Value('${executor.queueCapacity}') private Integer queueCapacity; /** 為每個線程名設(shè)置一個前綴（1） */ @Value('${executor.threadNamePrefix}') private String threadNamePrefix; /** 為每個線程名設(shè)置一個前綴（2） */ @Value('${executor.threadNamePrefix_2}') private String threadNamePrefix_2; @Bean(ExecutorConstant.simpleExecutor_1) @Override public Executor getAsyncExecutor() {//線程池ThreadPoolTaskExecutor taskExecutor = new ThreadPoolTaskExecutor();taskExecutor.setCorePoolSize(corePoolSize);taskExecutor.setMaxPoolSize(maxPoolSize);taskExecutor.setQueueCapacity(queueCapacity);taskExecutor.setThreadNamePrefix(threadNamePrefix);taskExecutor.initialize();return taskExecutor; } @Bean(ExecutorConstant.simpleExecutor_2) public Executor asyncExecutor2() {//線程池ThreadPoolTaskExecutor taskExecutor = new ThreadPoolTaskExecutor();taskExecutor.setCorePoolSize(corePoolSize);taskExecutor.setMaxPoolSize(maxPoolSize);taskExecutor.setQueueCapacity(queueCapacity);taskExecutor.setThreadNamePrefix(threadNamePrefix_2);taskExecutor.initialize();return taskExecutor; }}2、如何使用@Async

下面是代碼:TestAsyncService類：

@Slf4j@Servicepublic class TestAsyncService implements ITestAsyncService { /** * 異步方法，無返回值 * @return */ @Async @Override public void asyncFunction_1(){handleBusinessTime();log.info('asyncFunction_1 當(dāng)前線程名稱是：{}',Thread.currentThread().getName()); }; /////////////////異步方法，無返回值(指定線程池) start /** * 異步方法，無返回值(指定線程池) * @return */ @Async(value = ExecutorConstant.simpleExecutor_2) @Override public void asyncFunction_2(){handleBusinessTime();log.info('asyncFunction_2 當(dāng)前線程名稱是：{}',Thread.currentThread().getName()); }; @Async(ExecutorConstant.simpleExecutor_2) @Override public void asyncFunction_3(){handleBusinessTime();log.info('asyncFunction_3 當(dāng)前線程名稱是：{}',Thread.currentThread().getName()); }; /////////////////異步方法，無返回值(指定線程池) end /** * 異步方法，有返回值 * @return */ @Async @Override public Future<Integer> asyncReturnDta_1(){handleBusinessTime();log.info('asyncReturnDta_1 當(dāng)前線程名稱是：{}',Thread.currentThread().getName());return new AsyncResult<Integer>(1); }; /** * 異步方法，有返回值(指定線程池) * @return */ @Async(ExecutorConstant.simpleExecutor_2) @Override public Future<Integer> asyncReturnDta_2(){handleBusinessTime();log.info('asyncReturnDta_2 當(dāng)前線程名稱是：{}',Thread.currentThread().getName());return new AsyncResult<Integer>(1); }; /** * 異步方法，有返回值-超時 * @return */ @Async @Override public Future<Integer> asyncReturnDtaTimeOut(){handleBusinessTime();handleBusinessTime();handleBusinessTime();handleBusinessTime();log.info('asyncReturnDta_3 當(dāng)前線程名稱是：{}',Thread.currentThread().getName());return new AsyncResult<Integer>(1); }; /** * 這方法 模擬處理業(yè)務(wù)或者 去操作數(shù)據(jù)庫 消耗的時間 */ public static void handleBusinessTime(){//去數(shù)據(jù)庫查詢數(shù)據(jù)耗時 startint[] sleepTime = NumberUtil.generateRandomNumber(2000,5000,1);try { //Thread.sleep 休眠的時候 相當(dāng)于 業(yè)務(wù)操作，或者請求數(shù)據(jù)庫的需要消耗的時間 Thread.sleep(sleepTime[0]);} catch (InterruptedException e) { e.printStackTrace();}//去數(shù)據(jù)庫查詢數(shù)據(jù)耗時 end }}

TestAsyncController

@Slf4j@RestController@RequestMapping(value = '/v1/async')public class TestAsyncController { @Autowired ITestAsyncService testAsyncService; @ApiOperation(value = '調(diào)用接口') @RequestMapping(value = '/test', method = RequestMethod.GET) public Resp<Integer> test() throws ExecutionException, InterruptedException {log.info('asyncFunction_1 start');testAsyncService.asyncFunction_1();log.info('asyncFunction_1 start');log.info('asyncFunction_2 start');testAsyncService.asyncFunction_2();log.info('asyncFunction_2 end');log.info('asyncFunction_3 start');testAsyncService.asyncFunction_3();log.info('asyncFunction_3 end');log.info('asyncReturnDta_1 & asyncReturnDta_2 start');Future<Integer> future = testAsyncService.asyncReturnDta_1();testAsyncService.asyncReturnDta_2();log.info('asyncReturnDta_1 & asyncReturnDta_2 end');Integer resp = future.get();log.info('future.get() resp:{}',resp);return Resp.buildDataSuccess(resp); } @ApiOperation(value = '調(diào)用接口-超時') @RequestMapping(value = '/async_timeOut', method = RequestMethod.GET) public Resp<Integer> async_timeOut() throws ExecutionException, InterruptedException {TimeInterval timeInterval = DateUtil.timer();log.info('asyncReturnDtaTimeOut start');Future<Integer> future = testAsyncService.asyncReturnDtaTimeOut();log.info('asyncReturnDtaTimeOut end');Integer resp = null;try { //一秒內(nèi) 返回不了數(shù)據(jù)就報錯 resp = future.get(1, TimeUnit.SECONDS);} catch (TimeoutException e) { resp = -1;//請求超時了，相當(dāng)于熔斷，服務(wù)降級 log.error('asyncReturnDtaTimeOut future.get(1, TimeUnit.SECONDS) timeout:',e);}log.info('future.get() resp:{} 耗時：{}毫秒',resp,timeInterval.intervalRestart());return Resp.buildDataSuccess(resp); }}

/v1/async/test 接口：

2021-06-20 21:09:30.490 INFO 14207 --- [nio-8666-exec-7] c.e.m.controller.TestAsyncController : asyncFunction_1 start2021-06-20 21:09:30.490 INFO 14207 --- [nio-8666-exec-7] c.e.m.controller.TestAsyncController : asyncFunction_1 start2021-06-20 21:09:30.490 INFO 14207 --- [nio-8666-exec-7] c.e.m.controller.TestAsyncController : asyncFunction_2 start2021-06-20 21:09:30.491 INFO 14207 --- [nio-8666-exec-7] c.e.m.controller.TestAsyncController : asyncFunction_2 end2021-06-20 21:09:30.491 INFO 14207 --- [nio-8666-exec-7] c.e.m.controller.TestAsyncController : asyncFunction_3 start2021-06-20 21:09:30.491 INFO 14207 --- [nio-8666-exec-7] c.e.m.controller.TestAsyncController : asyncFunction_3 end2021-06-20 21:09:30.491 INFO 14207 --- [nio-8666-exec-7] c.e.m.controller.TestAsyncController : asyncReturnDta_1 & asyncReturnDta_2 start2021-06-20 21:09:30.492 INFO 14207 --- [nio-8666-exec-7] c.e.m.controller.TestAsyncController : asyncReturnDta_1 & asyncReturnDta_2 end2021-06-20 21:09:32.679 INFO 14207 --- [le-1-executor-9] c.e.multi.service.impl.TestAsyncService : asyncFunction_1 當(dāng)前線程名稱是：my-simple-1-executor-92021-06-20 21:09:33.454 INFO 14207 --- [le-2-executor-8] c.e.multi.service.impl.TestAsyncService : asyncFunction_3 當(dāng)前線程名稱是：my-simple-2-executor-82021-06-20 21:09:33.578 INFO 14207 --- [le-2-executor-9] c.e.multi.service.impl.TestAsyncService : asyncReturnDta_2 當(dāng)前線程名稱是：my-simple-2-executor-92021-06-20 21:09:34.101 INFO 14207 --- [e-1-executor-10] c.e.multi.service.impl.TestAsyncService : asyncReturnDta_1 當(dāng)前線程名稱是：my-simple-1-executor-102021-06-20 21:09:34.102 INFO 14207 --- [nio-8666-exec-7] c.e.m.controller.TestAsyncController : future.get() resp:12021-06-20 21:09:34.357 INFO 14207 --- [le-2-executor-7] c.e.multi.service.impl.TestAsyncService : asyncFunction_2 當(dāng)前線程名稱是：my-simple-2-executor-7

從日志上可以看出，都是異步執(zhí)行的

/v1/async/async_timeOut 接口：

2021-06-20 21:20:58.886 INFO 14427 --- [nio-8666-exec-1] c.e.m.controller.TestAsyncController : asyncReturnDtaTimeOut start2021-06-20 21:20:58.890 INFO 14427 --- [nio-8666-exec-1] c.e.m.controller.TestAsyncController : asyncReturnDtaTimeOut end2021-06-20 21:20:59.899 ERROR 14427 --- [nio-8666-exec-1] c.e.m.controller.TestAsyncController : asyncReturnDtaTimeOut future.get(1, TimeUnit.SECONDS) timeout:

java.util.concurrent.TimeoutException: nullat java.util.concurrent.FutureTask.get(FutureTask.java:205) ~[na:1.8.0_231]at com.example.multi.controller.TestAsyncController.async_timeOut(TestAsyncController.java:69) ~[classes/:na]at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_231]at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_231]at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_231]at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_231]at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:197) [spring-web-5.3.8.jar:5.3.8]at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:141) [spring-web-5.3.8.jar:5.3.8]at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:106) [spring-webmvc-5.3.8.jar:5.3.8]at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:894) [spring-webmvc-5.3.8.jar:5.3.8]at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:808) [spring-webmvc-5.3.8.jar:5.3.8]at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87) [spring-webmvc-5.3.8.jar:5.3.8]at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1063) [spring-webmvc-5.3.8.jar:5.3.8]at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:963) [spring-webmvc-5.3.8.jar:5.3.8]at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006) [spring-webmvc-5.3.8.jar:5.3.8]at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:898) [spring-webmvc-5.3.8.jar:5.3.8]at javax.servlet.http.HttpServlet.service(HttpServlet.java:626) [tomcat-embed-core-9.0.46.jar:4.0.FR]at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883) [spring-webmvc-5.3.8.jar:5.3.8]at javax.servlet.http.HttpServlet.service(HttpServlet.java:733) [tomcat-embed-core-9.0.46.jar:4.0.FR]at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:227) [tomcat-embed-core-9.0.46.jar:9.0.46]at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) [tomcat-embed-core-9.0.46.jar:9.0.46]at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53) [tomcat-embed-websocket-9.0.46.jar:9.0.46]at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) [tomcat-embed-core-9.0.46.jar:9.0.46]at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) [tomcat-embed-core-9.0.46.jar:9.0.46]at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100) [spring-web-5.3.8.jar:5.3.8]at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) [spring-web-5.3.8.jar:5.3.8]at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) [tomcat-embed-core-9.0.46.jar:9.0.46]at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) [tomcat-embed-core-9.0.46.jar:9.0.46]at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93) [spring-web-5.3.8.jar:5.3.8]at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) [spring-web-5.3.8.jar:5.3.8]at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) [tomcat-embed-core-9.0.46.jar:9.0.46]at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) [tomcat-embed-core-9.0.46.jar:9.0.46]at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201) [spring-web-5.3.8.jar:5.3.8]at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) [spring-web-5.3.8.jar:5.3.8]at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) [tomcat-embed-core-9.0.46.jar:9.0.46]at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) [tomcat-embed-core-9.0.46.jar:9.0.46]at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202) [tomcat-embed-core-9.0.46.jar:9.0.46]at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:97) [tomcat-embed-core-9.0.46.jar:9.0.46]at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:542) [tomcat-embed-core-9.0.46.jar:9.0.46]at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:143) [tomcat-embed-core-9.0.46.jar:9.0.46]at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) [tomcat-embed-core-9.0.46.jar:9.0.46]at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:78) [tomcat-embed-core-9.0.46.jar:9.0.46]at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:357) [tomcat-embed-core-9.0.46.jar:9.0.46]at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:374) [tomcat-embed-core-9.0.46.jar:9.0.46]at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65) [tomcat-embed-core-9.0.46.jar:9.0.46]at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:893) [tomcat-embed-core-9.0.46.jar:9.0.46]at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1707) [tomcat-embed-core-9.0.46.jar:9.0.46]at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) [tomcat-embed-core-9.0.46.jar:9.0.46]at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [na:1.8.0_231]at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [na:1.8.0_231]at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-embed-core-9.0.46.jar:9.0.46]at java.lang.Thread.run(Thread.java:748) [na:1.8.0_231]

2021-06-20 21:20:59.900 INFO 14427 --- [nio-8666-exec-1] c.e.m.controller.TestAsyncController : future.get() resp:-1 耗時：1014毫秒2021-06-20 21:21:12.105 INFO 14427 --- [le-1-executor-1] c.e.multi.service.impl.TestAsyncService : asyncReturnDta_3 當(dāng)前線程名稱是：my-simple-1-executor-1

從日志上看出，如果future.get(1, TimeUnit.SECONDS) 到了超時時間，直接拋出超時異常，走主線程后續(xù)代碼。比較適合 規(guī)定時間范圍內(nèi)要返回數(shù)據(jù)（超時可以根據(jù)業(yè)務(wù)場景，返回一個默認(rèn)值，或者返回值值就是空的）的業(yè)務(wù)場景

原理：是通過spring aop + 線程池的方式來實現(xiàn)的源碼：源碼的方法位置是：AsyncExecutionInterceptor.invoke

107行：是獲取一個線程池108行：如果沒有設(shè)置線程池拋出異常113行：是創(chuàng)建一個線程對象 他的run方法執(zhí)行invocation.proceed()【走實際業(yè)務(wù)代碼】121和124行：走的是統(tǒng)一的異常處理 主要是調(diào)用handleUncaughtException方法，SimpleExecutorConfig 實現(xiàn)了AsyncConfigurer接口它就有g(shù)etAsyncUncaughtExceptionHandler方法，可以重寫這個方法，實現(xiàn)自定義的異常處理

下圖是AsyncConfigurer接口可以實現(xiàn)的方法：

doSubmit方法：

實際上就是調(diào)用線程池的submit方法：

具體代碼，我上傳到gitee，大家感興趣可以clone 傳送門～

@Async源碼參考于：https://www.jb51.net/article/141542.htm

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