SpringBoot集成篇（二） 异步调用Async
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：
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org.springframework.boot
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spring-boot-starter-parent
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1.5.3.RELEASE
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org.springframework.boot
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spring-boot-starter-web
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@SpringBootApplication
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@EnableAsync
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public
class Application{
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public static void main(String[] args) {
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SpringApplication.run(Application.class, args);
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}
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}
Controller
只需在需要异步执行方法上添加@Async注解
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@RestController
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@RequestMapping(
"")
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public
class AsyncTaskController {
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@RequestMapping(
"")
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public String doTask() throws InterruptedException{
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long currentTimeMillis = System.currentTimeMillis();
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this.task1();
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this.task2();
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this.task3();
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long currentTimeMillis1 = System.currentTimeMillis();
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return
"task任务总耗时:"+(currentTimeMillis1-currentTimeMillis)+
"ms";
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}
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@Async
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public void task1() throws InterruptedException{
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long currentTimeMillis = System.currentTimeMillis();
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Thread.sleep(
1000);
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long currentTimeMillis1 = System.currentTimeMillis();
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System.out.println(
"task1任务耗时:"+(currentTimeMillis1-currentTimeMillis)+
"ms");
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}
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@Async
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public void task2() throws InterruptedException{
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long currentTimeMillis = System.currentTimeMillis();
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Thread.sleep(
2000);
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long currentTimeMillis1 = System.currentTimeMillis();
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System.out.println(
"task2任务耗时:"+(currentTimeMillis1-currentTimeMillis)+
"ms");
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}
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@Async
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public void task3() throws InterruptedException{
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long currentTimeMillis = System.currentTimeMillis();
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Thread.sleep(
3000);
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long currentTimeMillis1 = System.currentTimeMillis();
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System.out.println(
"task3任务耗时:"+(currentTimeMillis1-currentTimeMillis)+
"ms");
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}
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}
http://localhost:8080/
控制台：
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
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@RequestMapping(
"")
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@RestController
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public
class AsyncTaskController {
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@Autowired
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private AsyncTask asyncTask;
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@RequestMapping(
"")
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public String doTask() throws InterruptedException{
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long currentTimeMillis = System.currentTimeMillis();
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asyncTask.task1();
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asyncTask.task2();
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asyncTask.task3();
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long currentTimeMillis1 = System.currentTimeMillis();
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return
"task任务总耗时:"+(currentTimeMillis1-currentTimeMillis)+
"ms";
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}
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}
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@Component
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public
class AsyncTask {
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@Async
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public void task1() throws InterruptedException{
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long currentTimeMillis = System.currentTimeMillis();
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Thread.sleep(
1000);
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long currentTimeMillis1 = System.currentTimeMillis();
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System.out.println(
"task1任务耗时:"+(currentTimeMillis1-currentTimeMillis)+
"ms");
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}
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@Async
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public void task2() throws InterruptedException{
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long currentTimeMillis = System.currentTimeMillis();
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Thread.sleep(
2000);
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long currentTimeMillis1 = System.currentTimeMillis();
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System.out.println(
"task2任务耗时:"+(currentTimeMillis1-currentTimeMillis)+
"ms");
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}
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@Async
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public void task3() throws InterruptedException{
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long currentTimeMillis = System.currentTimeMillis();
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Thread.sleep(
3000);
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long currentTimeMillis1 = System.currentTimeMillis();
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System.out.println(
"task3任务耗时:"+(currentTimeMillis1-currentTimeMillis)+
"ms");
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}
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}
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控制台：
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
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@Component
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public
class AsyncTask {
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@Async
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public Future
task1() throws InterruptedException {
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long currentTimeMillis = System.currentTimeMillis();
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Thread.sleep(
1000);
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long currentTimeMillis1 = System.currentTimeMillis();
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System.out.println(
"task1任务耗时:"+(currentTimeMillis1-currentTimeMillis)+
"ms");
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return
new AsyncResult
(
"task1执行完毕");
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}
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@Async
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public Future
task2() throws InterruptedException {
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long currentTimeMillis = System.currentTimeMillis();
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Thread.sleep(
2000);
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long currentTimeMillis1 = System.currentTimeMillis();
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System.out.println(
"task2任务耗时:"+(currentTimeMillis1-currentTimeMillis)+
"ms");
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return
new AsyncResult
(
"task2执行完毕");
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}
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@Async
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public Future
task3() throws InterruptedException {
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long currentTimeMillis = System.currentTimeMillis();
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Thread.sleep(
3000);
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long currentTimeMillis1 = System.currentTimeMillis();
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System.out.println(
"task3任务耗时:"+(currentTimeMillis1-currentTimeMillis)+
"ms");
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return
new AsyncResult
(
"task3执行完毕");
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}
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}
Controller
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@RequestMapping(
"")
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@RestController
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public
class AsyncTaskController {
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@Autowired
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private AsyncTask asyncTask;
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@RequestMapping(
"")
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public String doTask() throws InterruptedException{
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long currentTimeMillis = System.currentTimeMillis();
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Future
task1 = asyncTask.task1();
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Future
task2 = asyncTask.task2();
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Future
task3 = asyncTask.task3();
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String result =
null;
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for (;;) {
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if(task1.isDone() && task2.isDone() && task3.isDone()) {
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// 三个任务都调用完成，退出循环等待
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break;
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}
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Thread.sleep(
1000);
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}
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long currentTimeMillis1 = System.currentTimeMillis();
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result =
"task任务总耗时:"+(currentTimeMillis1-currentTimeMillis)+
"ms";
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return result;
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}
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}
控制台输出：
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！