前言
通常情况下，SpringMVC接收到请求后会将请求具体分发给单个线程进行处理。如果请求处理中涉及到比较耗时的操作，为了能更快地将响应返回给用户，那么就需要将耗时的业务操作交由别的线程进行异步处理，而SpringBoot已经为我们提供了这样的实现。
@Async注解
新建一个AsyncController，给需要异步执行的方法加上@Async注解，代码如下：
package geek.springboot.application.controller;
import lombok.extern.slf4j.Slf4j;
import org.springframework.scheduling.annotation.Async;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
@Slf4j
@RequestMapping("/async/")
@RestController
public class AsyncController {
@GetMapping
public void processGet() {
log.info("start process get");
this.doSomeThing();
}
// 给需要异步执行的方法加上@Async
@Async
public void doSomeThing() {
log.info("do some thing");
}
}
需要开启SpringBoot异步任务执行功能，还需要加上@EnableAsync注解，在SpringApplication启动类加上，代码如下：
package geek.springboot.application;
import lombok.extern.slf4j.Slf4j;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.scheduling.annotation.EnableAsync;
@EnableAsync // 开启异步任务执行功能
@Slf4j
@SpringBootApplication
public class Application {
public static void main(String[] args) {
SpringApplication.run(Application.class, args);
}
}
@Async无效的原因
启动后Get /async/ ，控制台输出如下：
可以看到执行doSomeThing()的线程和处理Get请求的线程是同一个，都是nio-8080-exec-1，那这里之所以@Async注解无效，这是因为Spring是给扫描到的每个Bean都创建代理对象（@Component、@Service、@Controller...），而只有这些代理对象才做了方法增强，调用代理对象的方法才能实现我们期望的行为。比如@Async、@Transactional...
所以@Async无效的问题在于AsyncController中，this.doSomeThing();调用的不是代理对象的doSomeThing()，而是当前对象this的doSomeThing().
明白了问题的根源，那么新建一个AsyncService，代码如下：
package geek.springboot.application.service;
import lombok.extern.slf4j.Slf4j;
import org.springframework.scheduling.annotation.Async;
import org.springframework.stereotype.Service;
import java.util.concurrent.TimeUnit;
@Slf4j
@Service
public class AsyncService {
// 给需要异步执行的方法加上@Async
@Async
public void doSomeThing() {
// 为了演示线程池的效果,这里模拟耗时操作
try {
TimeUnit.SECONDS.sleep(2);
} catch (InterruptedException e) {
e.printStackTrace();
}
log.info("do some thing");
}
}
将AsyncController稍作调整
package geek.springboot.application.controller;
import geek.springboot.application.service.AsyncService;
import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
@Slf4j
@RequestMapping("/async/")
@RestController
public class AsyncController {
@Autowired
private AsyncService asyncService;
@GetMapping
public void processGet() {
log.info("start process get");
// 调用代理对象上@Async修饰的方法
this.asyncService.doSomeThing();
}
}
Get /asysnc/ ，输出如下：
可以看到doSomeThing()和processGet()不是同一个线程，异步处理成功。
@Async无效的其他原因
void或者Future 。自定义异步线程池
@Async本质，其实就是SpringBoot默认给我们封装好了一个线程池，所有Spring代理对象的@Async修饰方法，都会被扔到线程池中执行，从而不影响Http请求线程处理逻辑。而自定义的方式有如下几种：
application.yml
最简单的，通过application.yml自定义线程池
spring:
task:
execution:
# 核心线程数1，最大线程数2，任务队列容量为0，除核心线程外的线程空闲时存活时间60秒
pool:
core-size: 1
max-size: 2
queue-capacity: 0
keep-alive: "60s"
短时间内多次Get /async/ ，输出如下：
说明线程池配置生效，每一次doSomeThing()执行，都是由线程池中的线程轮流处理。
还可能出现以下错误，原因是当时线程池全部线程都在执行doSomeThing()，同时因为任务队列容量为0，所以再有新的doSomeThing()任务，直接被拒绝
2023-07-28 05:24:14.496 ERROR 39436 --- [nio-8080-exec-6] o.a.c.c.C.[.[.[/].[dispatcherServlet] : Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is org.springframework.core.task.TaskRejectedException: Executor [java.util.concurrent.ThreadPoolExecutor@1a67c1cf[Running, pool size = 2, active threads = 2, queued tasks = 0, completed tasks = 2]] did not accept task: org.springframework.aop.interceptor.AsyncExecutionInterceptor$$Lambda$665/842994983@196a33ce] with root cause
java.util.concurrent.RejectedExecutionException: Task java.util.concurrent.FutureTask@17adcf4b rejected from java.util.concurrent.ThreadPoolExecutor@1a67c1cf[Running, pool size = 2, active threads = 2, queued tasks = 0, completed tasks = 2]
at java.util.concurrent.ThreadPoolExecutor$AbortPolicy.rejectedExecution(ThreadPoolExecutor.java:2063) ~[na:1.8.0_241]
at java.util.concurrent.ThreadPoolExecutor.reject(ThreadPoolExecutor.java:830) ~[na:1.8.0_241]
at java.util.concurrent.ThreadPoolExecutor.execute(ThreadPoolExecutor.java:1379) ~[na:1.8.0_241]
at java.util.concurrent.AbstractExecutorService.submit(AbstractExecutorService.java:134) ~[na:1.8.0_241]
at org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor.submit(ThreadPoolTaskExecutor.java:388) ~[spring-context-5.3.29.jar:5.3.29]
at org.springframework.aop.interceptor.AsyncExecutionAspectSupport.doSubmit(AsyncExecutionAspectSupport.java:292) ~[spring-aop-5.3.29.jar:5.3.29]
at org.springframework.aop.interceptor.AsyncExecutionInterceptor.invoke(AsyncExecutionInterceptor.java:129) ~[spring-aop-5.3.29.jar:5.3.29]
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.3.29.jar:5.3.29]
at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.proceed(CglibAopProxy.java:763) ~[spring-aop-5.3.29.jar:5.3.29]
at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:708) ~[spring-aop-5.3.29.jar:5.3.29]
at geek.springboot.application.service.AsyncService$$EnhancerBySpringCGLIB$$ffc452ec.doSomeThing() ~[classes/:na]
at geek.springboot.application.controller.AsyncController.processGet(AsyncController.java:22) ~[classes/:na]
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_241]
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_241]
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_241]
at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_241]
at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:205) ~[spring-web-5.3.29.jar:5.3.29]
at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:150) ~[spring-web-5.3.29.jar:5.3.29]
at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:117) ~[spring-webmvc-5.3.29.jar:5.3.29]
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:895) ~[spring-webmvc-5.3.29.jar:5.3.29]
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:808) ~[spring-webmvc-5.3.29.jar:5.3.29]
at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87) ~[spring-webmvc-5.3.29.jar:5.3.29]
at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1072) ~[spring-webmvc-5.3.29.jar:5.3.29]
at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:965) ~[spring-webmvc-5.3.29.jar:5.3.29]
at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006) ~[spring-webmvc-5.3.29.jar:5.3.29]
at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:898) ~[spring-webmvc-5.3.29.jar:5.3.29]
at javax.servlet.http.HttpServlet.service(HttpServlet.java:529) ~[tomcat-embed-core-9.0.78.jar:4.0.FR]
at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883) ~[spring-webmvc-5.3.29.jar:5.3.29]
at javax.servlet.http.HttpServlet.service(HttpServlet.java:623) ~[tomcat-embed-core-9.0.78.jar:4.0.FR]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:209) ~[tomcat-embed-core-9.0.78.jar:9.0.78]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:153) ~[tomcat-embed-core-9.0.78.jar:9.0.78]
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:51) ~[tomcat-embed-websocket-9.0.78.jar:9.0.78]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:178) ~[tomcat-embed-core-9.0.78.jar:9.0.78]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:153) ~[tomcat-embed-core-9.0.78.jar:9.0.78]
at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100) ~[spring-web-5.3.29.jar:5.3.29]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117) ~[spring-web-5.3.29.jar:5.3.29]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:178) ~[tomcat-embed-core-9.0.78.jar:9.0.78]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:153) ~[tomcat-embed-core-9.0.78.jar:9.0.78]
at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93) ~[spring-web-5.3.29.jar:5.3.29]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117) ~[spring-web-5.3.29.jar:5.3.29]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:178) ~[tomcat-embed-core-9.0.78.jar:9.0.78]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:153) ~[tomcat-embed-core-9.0.78.jar:9.0.78]
at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201) ~[spring-web-5.3.29.jar:5.3.29]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117) ~[spring-web-5.3.29.jar:5.3.29]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:178) ~[tomcat-embed-core-9.0.78.jar:9.0.78]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:153) ~[tomcat-embed-core-9.0.78.jar:9.0.78]
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:167) ~[tomcat-embed-core-9.0.78.jar:9.0.78]
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:90) [tomcat-embed-core-9.0.78.jar:9.0.78]
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:481) [tomcat-embed-core-9.0.78.jar:9.0.78]
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:130) [tomcat-embed-core-9.0.78.jar:9.0.78]
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:93) [tomcat-embed-core-9.0.78.jar:9.0.78]
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74) [tomcat-embed-core-9.0.78.jar:9.0.78]
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343) [tomcat-embed-core-9.0.78.jar:9.0.78]
at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:390) [tomcat-embed-core-9.0.78.jar:9.0.78]
at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:63) [tomcat-embed-core-9.0.78.jar:9.0.78]
at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:926) [tomcat-embed-core-9.0.78.jar:9.0.78]
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1791) [tomcat-embed-core-9.0.78.jar:9.0.78]
at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:52) [tomcat-embed-core-9.0.78.jar:9.0.78]
at org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1191) [tomcat-embed-core-9.0.78.jar:9.0.78]
at org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:659) [tomcat-embed-core-9.0.78.jar:9.0.78]
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-embed-core-9.0.78.jar:9.0.78]
at java.lang.Thread.run(Thread.java:748) [na:1.8.0_241]
ThreadPoolTaskExecutor
自定义ThreadPoolTaskExecutor，并作为Spring中的Bean存在，代码如下：
package geek.springboot.application.configuration;
import lombok.extern.slf4j.Slf4j;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor;
import java.util.concurrent.atomic.AtomicInteger;
/**
* 任务执行Config
*
* @author Bruse
*/
@Slf4j
@Configuration
public class TaskExecutorConfig {
private final AtomicInteger threadSeq = new AtomicInteger(0);
@Bean
public ThreadPoolTaskExecutor taskExecutor() {
ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
// 核心线程数
executor.setCorePoolSize(2);
// 最大线程数
executor.setMaxPoolSize(2);
// 空闲线程存活时间,单位:秒
executor.setKeepAliveSeconds(60);
// 任务队列容量
executor.setQueueCapacity(0);
// 线程名称前缀,如果设置了线程池工厂自定义线程,那么设置该参数无效
executor.setThreadNamePrefix("async task_");
// 自定义线程工厂,可以在这里自定义线程池中线程的一些参数
executor.setThreadFactory(r -> {
Thread thread = new Thread(r);
thread.setName("async task_" + threadSeq.getAndIncrement());
thread.setUncaughtExceptionHandler((t, e) -> log.error("线程抛出未捕获异常 {} {}", t.getName(), e.getMessage()));
return thread;
});
// 任务拒绝策略,实现RejectedExecutionHandler接口,自定义处理逻辑
executor.setRejectedExecutionHandler((r, executor1) -> log.error("任务被拒绝"));
// 或者使用ThreadPoolExecutor现有的拒绝策略
// executor.setRejectedExecutionHandler(new ThreadPoolExecutor.AbortPolicy());
return executor;
}
}
再次短时间内多次请求，输出如下：
可以看到设置到拒绝策略，线程名称等符合预期。
TaskExecutorBuilder
除了上面实例化ThreadPoolTaskExecutor的方式，也可以通过TaskExecutorBuilder自定义线程池，使用TaskExecutorBuilder最终也是构建出ThreadPoolTaskExecutor，代码如下：
@Bean
public ThreadPoolTaskExecutor taskExecutor() {
TaskExecutorBuilder builder = new TaskExecutorBuilder()
.corePoolSize(2)
.maxPoolSize(2)
.threadNamePrefix("async thread_")
.queueCapacity(0)
.keepAlive(Duration.ofSeconds(60))
.taskDecorator(runnable -> {
// 装饰者模式,这里可以在线程执行任务前,做一些额外操作
log.info("任务将要执行");
return runnable;
});
return builder.build();
}
输出如下：
或者直接定义一个TaskExecutorBuilder Bean，那么SpringBoot创建的ThreadPoolTaskExecutor将会使用该builder进行构建，代码如下：
@Bean
public TaskExecutorBuilder executorBuilder() {
return new TaskExecutorBuilder()
.corePoolSize(2)
.maxPoolSize(2)
.threadNamePrefix("async thread_")
.queueCapacity(0)
.keepAlive(Duration.ofSeconds(60))
.taskDecorator(runnable -> {
// 装饰者模式,这里可以在线程执行任务前,做一些额外操作
log.info("任务将要执行");
return runnable;
});
}
定时任务
@Scheduled
SpringBoot提供了简单的定时任务实现，只需要使用@EnableScheduling和@Scheduled这两个注解，新建一个SyncTask，代码如下：
package geek.springboot.application.task;
import lombok.extern.slf4j.Slf4j;
import org.springframework.scheduling.annotation.EnableScheduling;
import org.springframework.scheduling.annotation.Scheduled;
import org.springframework.stereotype.Component;
/**
* 定时同步
*
* @author Bruse
*/
@Slf4j
@EnableScheduling // 开启定时任务
@Component
public class SyncTask {
// 在要执行的方法上加上@Scheduled注解，这里表示每5秒执行一次sync()
@Scheduled(cron = "0/5 * * * * ?")
public void sync() {
log.info("do sync task ...");
}
}
启动后控制台输出如下：
application.yml
定时任务线程池也可以通过application.yml自定义，演示代码如下：
spring:
task:
scheduling:
thread-name-prefix: "scheduling-"
pool:
size: 2
再次重启，控制台输出如下，可以看到定时任务线程池的线程名称前缀已生效：
ThreadPoolTaskScheduler
SpringBoot定时任务执行底层实现依赖于ThreadPoolTaskScheduler，我们也可以自行创建ThreadPoolTaskScheduler并注册到Spring中来进行自定义，代码如下：
@Bean
public ThreadPoolTaskScheduler taskScheduler() {
return new TaskSchedulerBuilder()
// 线程名称前缀
.threadNamePrefix("scheduling-")
// 线程数
.poolSize(1)
.build();
}
TaskSchedulerBuilder
也可以自行创建TaskSchedulerBuilder，并注册到Spring中，那么SpringBoot在创建定时任务线程池时，则会按照该builder来进行线程池的创建，代码如下：
@Bean
public TaskSchedulerBuilder schedulerBuilder() {
return new TaskSchedulerBuilder()
// 线程名称前缀
.threadNamePrefix("schedule-")
// 线程数
.poolSize(1);
}
注意
ThreadPoolTaskScheduler默认线程数只有1，所以如果执行的任务过于耗时，那么则不能执行任务时都非常准时，SyncTask稍作如下调整：
@Scheduled(cron = "0/5 * * * * ?")
public void sync() {
// 模拟耗时操作
try {
TimeUnit.SECONDS.sleep(6);
} catch (InterruptedException e) {
throw new RuntimeException(e);
}
log.info("do sync task ...");
}
在不修改线程数的情况下，期望sync()每5秒执行一次，实际sync()执行耗时6秒，那么输出如下：
可以看到sync()里每次log打印的时间间隔都大于5秒。
那么是不是调整线程数就可以了呢？答案是否定的。就算把线程数调整为2，重启后输出可以看到，sync()每次打印的时间间隔还是大于5秒。
因为sync()这个需要定时执行的任务，已经和ThreadPoolTaskScheduler中的某个线程绑定了，sync()将由这个线程一直负责处理。
调整线程数的意义在于如果有多个定时任务需要处理的时候，需要将不同的定时任务交由更多的线程进行处理。
比如在线程数默认为1的情况下，新建另一个需要定时调用的方法doSomeThing():
@Scheduled(cron = "0/5 * * * * ?")
public void doSomeThing() {
try {
TimeUnit.SECONDS.sleep(6);
} catch (InterruptedException e) {
throw new RuntimeException(e);
}
log.info("do some thing ...");
}
启动后输出如下，可以看到系统中已有的定时任务都交由单个线程处理：
那这个时候我们把线程数调整为2，重启后输出如下：
这次2个定时任务分别交由2个线程进行处理，互不干扰了。
结尾
本文章源自《Learn SpringBoot》专栏，感兴趣的话还请关注点赞收藏.
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