1、java的大部分接口的方法都是串行執行的，但是有些業務場景是不需要同步返回結果的，可以把結果直接返回，具體業務異步執行，也有些業務接口是需要並行獲取數據，最后把數據聚合在統一返回給前端。
通常我們都是采用多線程的方式來實現上述業務功能，但spring 提供更優雅的方式來實現上述功能，就是@Async 異步注解，在方法上添加@Async，spring就會借助AOP，異步執行方法。
1、如何啟用@Async
spring boot通過@EnableAsync 注解啟用@Async異步注解
實現AsyncConfigurer接口，getAsyncExecutor是默認自定義的線程池
/**
* 線程池配置（@Async）
*/
@Slf4j
@EnableAsync
@Configuration
public class SimpleExecutorConfig implements AsyncConfigurer {
/** 線程池維護線程的最少數量 */
@Value("${executor.corePoolSize}")
private Integer corePoolSize;
/** 線程池維護線程的最大數量 */
@Value("${executor.maxPoolSize}")
private Integer maxPoolSize;
/** 緩沖隊列的大小 */
@Value("${executor.queueCapacity}")
private Integer queueCapacity;
/** 為每個線程名設置一個前綴（1） */
@Value("${executor.threadNamePrefix}")
private String threadNamePrefix;
/** 為每個線程名設置一個前綴（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
@Service
public 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 當前線程名稱是：{}",Thread.currentThread().getName());
};
@Async(ExecutorConstant.simpleExecutor_2)
@Override
public void asyncFunction_3(){
handleBusinessTime();
log.info("asyncFunction_3 當前線程名稱是：{}",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 當前線程名稱是：{}",Thread.currentThread().getName());
return new AsyncResult<Integer>(1);
};
/**
* 這方法 模擬處理業務或者 去操作數據庫 消耗的時間
*/
public static void handleBusinessTime(){
//去數據庫查詢數據耗時 start
int[] sleepTime = NumberUtil.generateRandomNumber(2000,5000,1);
try {
//Thread.sleep 休眠的時候 相當於 業務操作，或者請求數據庫的需要消耗的時間
Thread.sleep(sleepTime[0]);
} catch (InterruptedException e) {
e.printStackTrace();
}
//去數據庫查詢數據耗時 end
}
}
TestAsyncController
@Slf4j
@RestController
@RequestMapping(value = "/v1/async")
public class TestAsyncController {
@Autowired
ITestAsyncService testAsyncService;
@ApiOperation(value = "調用接口")
@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 返回不了數據就報錯
resp = future.get(1, TimeUnit.SECONDS);
} catch (TimeoutException e) {
resp = -1;//請求超時了，相當於熔斷，服務降級
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 start
2021-06-20 21:09:30.490 INFO 14207 --- [nio-8666-exec-7] c.e.m.controller.TestAsyncController : asyncFunction_1 start
2021-06-20 21:09:30.490 INFO 14207 --- [nio-8666-exec-7] c.e.m.controller.TestAsyncController : asyncFunction_2 start
2021-06-20 21:09:30.491 INFO 14207 --- [nio-8666-exec-7] c.e.m.controller.TestAsyncController : asyncFunction_2 end
2021-06-20 21:09:30.491 INFO 14207 --- [nio-8666-exec-7] c.e.m.controller.TestAsyncController : asyncFunction_3 start
2021-06-20 21:09:30.491 INFO 14207 --- [nio-8666-exec-7] c.e.m.controller.TestAsyncController : asyncFunction_3 end
2021-06-20 21:09:30.491 INFO 14207 --- [nio-8666-exec-7] c.e.m.controller.TestAsyncController : asyncReturnDta_1 & asyncReturnDta_2 start
2021-06-20 21:09:30.492 INFO 14207 --- [nio-8666-exec-7] c.e.m.controller.TestAsyncController : asyncReturnDta_1 & asyncReturnDta_2 end
2021-06-20 21:09:32.679 INFO 14207 --- [le-1-executor-9] c.e.multi.service.impl.TestAsyncService : asyncFunction_1 當前線程名稱是：my-simple-1-executor-9
2021-06-20 21:09:33.454 INFO 14207 --- [le-2-executor-8] c.e.multi.service.impl.TestAsyncService : asyncFunction_3 當前線程名稱是：my-simple-2-executor-8
2021-06-20 21:09:33.578 INFO 14207 --- [le-2-executor-9] c.e.multi.service.impl.TestAsyncService : asyncReturnDta_2 當前線程名稱是：my-simple-2-executor-9
2021-06-20 21:09:34.101 INFO 14207 --- [e-1-executor-10] c.e.multi.service.impl.TestAsyncService : asyncReturnDta_1 當前線程名稱是：my-simple-1-executor-10
2021-06-20 21:09:34.102 INFO 14207 --- [nio-8666-exec-7] c.e.m.controller.TestAsyncController : future.get() resp:1
2021-06-20 21:09:34.357 INFO 14207 --- [le-2-executor-7] c.e.multi.service.impl.TestAsyncService : asyncFunction_2 當前線程名稱是：my-simple-2-executor-7
從日志上可以看出，都是異步執行的
/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 start
2021-06-20 21:20:58.890 INFO 14427 --- [nio-8666-exec-1] c.e.m.controller.TestAsyncController : asyncReturnDtaTimeOut end
2021-06-20 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: null
at 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，走主線程后續代碼。
比較適合 規定時間范圍內要返回數據（超時可以根據業務場景，返回一個默認值，或者返回值值就是空的）的業務場景
@Async原理+源碼
原理：是通過spring aop + 線程池的方式來實現的
源碼：
源碼的方法位置是：AsyncExecutionInterceptor.invoke
- 107行：是獲取一個線程池
- 108行：如果沒有設置線程池拋出異常
- 113行：是創建一個線程對象 他的run方法執行invocation.proceed()【走實際業務代碼】
- 121和124行：走的是統一的異常處理 主要是調用handleUncaughtException方法，SimpleExecutorConfig 實現了AsyncConfigurer接口它就有getAsyncUncaughtExceptionHandler方法，可以重寫這個方法，實現自定義的異常處理
下圖是AsyncConfigurer接口可以實現的方法：
doSubmit方法：
實際上就是調用線程池的submit方法：
具體代碼，我上傳到gitee，大家感興趣可以clone 傳送門～
@Async源碼參考於：
https://www.cnblogs.com/dennyzhangdd/p/9026303.html