SpringBoot多线程异步调用 @Async
2020-02-21 本文已影响0人
Liopisces
1. 什么是异步调用?
异步调用是相对于同步调用而言的,同步调用是指程序按预定顺序一步步执行,每一步必须等到上一步执行完后才能执行,异步调用则无需等待上一步程序执行完即可执行。
2.如何实现异步调用?
多线程,这是很多人第一眼想到的关键词,没错,多线程就是一种实现异步调用的方式。
在非spring目项目中我们要实现异步调用的就是使用多线程方式,可以自己实现Runable接口或者集成Thread类,或者使用jdk1.5以上提供了的Executors线程池。
SpringBoot中则提供了很方便的方式执行异步调用。
3. 异步接口的使用场景
耗时比较长,任务比较多的接口。比方说,文件下载,大文件下载比较耗时,这个时候就可以使用异步接口。
示例1
代码入下:
maven依赖:
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>1.5.3.RELEASE</version>
</parent>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
</dependencies>
启动类:添加@EnableAsync注解
@SpringBootApplication
@EnableAsync
public class Application{
public static void main(String[] args) {
SpringApplication.run(Application.class, args);
}
}
Controller
只需在需要异步执行方法上添加@Async注解
@RestController
@RequestMapping("")
public class AsyncTaskController {
@RequestMapping("")
public String doTask() throws InterruptedException{
long currentTimeMillis = System.currentTimeMillis();
this.task1();
this.task2();
this.task3();
long currentTimeMillis1 = System.currentTimeMillis();
return "task任务总耗时:"+(currentTimeMillis1-currentTimeMillis)+"ms";
}
@Async
public void task1() throws InterruptedException{
long currentTimeMillis = System.currentTimeMillis();
Thread.sleep(1000);
long currentTimeMillis1 = System.currentTimeMillis();
System.out.println("task1任务耗时:"+(currentTimeMillis1-currentTimeMillis)+"ms");
}
@Async
public void task2() throws InterruptedException{
long currentTimeMillis = System.currentTimeMillis();
Thread.sleep(2000);
long currentTimeMillis1 = System.currentTimeMillis();
System.out.println("task2任务耗时:"+(currentTimeMillis1-currentTimeMillis)+"ms");
}
@Async
public void task3() throws InterruptedException{
long currentTimeMillis = System.currentTimeMillis();
Thread.sleep(3000);
long currentTimeMillis1 = System.currentTimeMillis();
System.out.println("task3任务耗时:"+(currentTimeMillis1-currentTimeMillis)+"ms");
}
}
控制台:
result1.png
result2.png
异步并没有执行
难道是代码写错了?反复检查了好几遍,并没有发现什么明显错误,想起spring对@Transactional注解时也有类似问题,spring扫描时具有@Transactional注解方法的类时,是生成一个代理类,由代理类去开启关闭事务,而在同一个类中,方法调用是在类体内执行的,spring无法截获这个方法调用。
豁然开朗,将异步任务单独放到一个类中,调整代码入下:
Controller
@RequestMapping("")
@RestController
public class AsyncTaskController {
//将异步方法抽离不放在同一个类中
@Autowired
private AsyncTask asyncTask;
@RequestMapping("")
public String doTask() throws InterruptedException{
long currentTimeMillis = System.currentTimeMillis();
asyncTask.task1();
asyncTask.task2();
asyncTask.task3();
long currentTimeMillis1 = System.currentTimeMillis();
return "task任务总耗时:"+(currentTimeMillis1-currentTimeMillis)+"ms";
}
}
异步任务类
@Component
public class AsyncTask {
@Async
public void task1() throws InterruptedException{
long currentTimeMillis = System.currentTimeMillis();
Thread.sleep(1000);
long currentTimeMillis1 = System.currentTimeMillis();
System.out.println("task1任务耗时:"+(currentTimeMillis1-currentTimeMillis)+"ms");
}
@Async
public void task2() throws InterruptedException{
long currentTimeMillis = System.currentTimeMillis();
Thread.sleep(2000);
long currentTimeMillis1 = System.currentTimeMillis();
System.out.println("task2任务耗时:"+(currentTimeMillis1-currentTimeMillis)+"ms");
}
@Async
public void task3() throws InterruptedException{
long currentTimeMillis = System.currentTimeMillis();
Thread.sleep(3000);
long currentTimeMillis1 = System.currentTimeMillis();
System.out.println("task3任务耗时:"+(currentTimeMillis1-currentTimeMillis)+"ms");
}
}
控制台:
result3.png
result4.png
异步调用成功!
如何知道三个异步任务什么时候执行完,执行的结果怎样呢?可以采用添加Fature回调方式判断
代码入下:
异步任务类
@Component
public class AsyncTask {
@Async
public Future<String> task1() throws InterruptedException{
long currentTimeMillis = System.currentTimeMillis();
Thread.sleep(1000);
long currentTimeMillis1 = System.currentTimeMillis();
System.out.println("task1任务耗时:"+(currentTimeMillis1-currentTimeMillis)+"ms");
return new AsyncResult<String>("task1执行完毕");
}
@Async
public Future<String> task2() throws InterruptedException{
long currentTimeMillis = System.currentTimeMillis();
Thread.sleep(2000);
long currentTimeMillis1 = System.currentTimeMillis();
System.out.println("task2任务耗时:"+(currentTimeMillis1-currentTimeMillis)+"ms");
return new AsyncResult<String>("task2执行完毕");
}
@Async
public Future<String> task3() throws InterruptedException{
long currentTimeMillis = System.currentTimeMillis();
Thread.sleep(3000);
long currentTimeMillis1 = System.currentTimeMillis();
System.out.println("task3任务耗时:"+(currentTimeMillis1-currentTimeMillis)+"ms");
return new AsyncResult<String>("task3执行完毕");
}
}
Controller
@RequestMapping("")
@RestController
public class AsyncTaskController {
@Autowired
private AsyncTask asyncTask;
@RequestMapping("")
public String doTask() throws InterruptedException{
long currentTimeMillis = System.currentTimeMillis();
Future<String> task1 = asyncTask.task1();
Future<String> task2 = asyncTask.task2();
Future<String> task3 = asyncTask.task3();
String result = null;
for (;;) {
if(task1.isDone() && task2.isDone() && task3.isDone()) {
// 三个任务都调用完成,退出循环等待
break;
}
Thread.sleep(1000);
}
long currentTimeMillis1 = System.currentTimeMillis();
result = "task任务总耗时:"+(currentTimeMillis1-currentTimeMillis)+"ms";
return result;
}
}
控制台输出:
reslut5.png
result6.png
异步调用成功,并且在所有任务都完成时程序才返回了结果!
参考文章:
实战Spring Boot 2.0之@Async异步调用详解
springboot+async异步接口实现和调用