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。
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。
StrngBoot中则提供了很方便的方式执行异步调用。
按照官方示例开撸
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>
- public class Application{
- public static void main(String[] args) {
- SpringApplication.run(Application.class, args);
- }
- }
只需在需要异步执行方法上添加@Async注解
- "")(
- public class AsyncTaskController {
- "")(
- 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";
- }
- 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");
- }
- 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");
- }
- 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");
- }
- }
http://localhost:8080/
控制台:
- task1任务耗时:1012ms
- task2任务耗时:2009ms
- task3任务耗时:3004ms
等了一段浏览器时候输出入下:
task任务总耗时:6002ms
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
- "")(
- public class AsyncTaskController {
- private AsyncTask asyncTask;
- "")(
- 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";
- }
- }
- public class AsyncTask {
- 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");
- }
- 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");
- }
- 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:
- task1任务耗时:1012ms
- task2任务耗时:2009ms
- task3任务耗时:3004ms
访问浏览器结果入下:
task任务总耗时:19ms
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
- public class AsyncTask {
- 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");
- }
- 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");
- }
- 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
- "")(
- public class AsyncTaskController {
- private AsyncTask asyncTask;
- "")(
- 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:
- task1任务耗时:1000ms
- task2任务耗时:2001ms
- task3任务耗时:3001ms
浏览器输出:
task任务总耗时:4015ms
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!
文章转载自:https://blog.csdn.net/v2sking/article/details/72795742
文章来源: SpringBoot ――异步调用Async