什麼是異步調用?
異步調用是相對於同步調用而言的,同步調用是指程序按預定順序一步步執行,每一步必須等到上一步執行完後才能執行,異步調用則無需等待上一步程序執行完即可執行。
如何實現異步調用?
多線程,這是很多人第一眼想到的關鍵詞,沒錯,多線程就是一種實現異步調用的方式。
在非spring目項目中我們要實現異步調用的就是使用多線程方式,可以自己實現Runable接口或者集成Thread類,或者使用jdk1.5以上提供了的Executors線程池。
StrngBoot中則提供了很方便的方式執行異步調用。
按照官方示例開擼
代碼入下
maven依賴:
<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>
啓動類:添加@EnableAsync註解
@SpringBootApplication
@EnableAsync
public class Application{
public static void main(String[] args) {
SpringApplication.run(Application.class, args);
}
}
Controller
只需在需要異步執行方法上添加@Async註解
@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任務總耗時:"+(currentTimeMillis1-currentTimeMillis)+"ms";
}
@Async
public void task1() throws InterruptedException{
long currentTimeMillis = System.currentTimeMillis();
Thread.sleep(1000);
long currentTimeMillis1 = System.currentTimeMillis();
System.out.println("task1任務耗時:"+(currentTimeMillis1-currentTimeMillis)+"ms");
}
@Async
public void task2() throws InterruptedException{
long currentTimeMillis = System.currentTimeMillis();
Thread.sleep(2000);
long currentTimeMillis1 = System.currentTimeMillis();
System.out.println("task2任務耗時:"+(currentTimeMillis1-currentTimeMillis)+"ms");
}
@Async
public void task3() throws InterruptedException{
long currentTimeMillis = System.currentTimeMillis();
Thread.sleep(3000);
long currentTimeMillis1 = System.currentTimeMillis();
System.out.println("task3任務耗時:"+(currentTimeMillis1-currentTimeMillis)+"ms");
}
}
main函數運行spirngboot項目,啓動完成後瀏覽器訪問:
http://localhost:8080/
控制檯:
task1任務耗時:1012ms
task2任務耗時:2009ms
task3任務耗時:3004ms
等了一段瀏覽器時候輸出入下:
task任務總耗時:6002ms
異步並沒有執行!
難道是代碼寫錯了?反覆檢查了好幾遍,並沒有發現什麼明顯錯誤,想起spring對@Transactional註解時也有類似問題,spring掃描時具有@Transactional註解方法的類時,是生成一個代理類,由代理類去開啓關閉事務,而在同一個類中,方法調用是在類體內執行的,spring無法截獲這個方法調用。
豁然開朗,將異步任務單獨放到一個類中,調整代碼入下:
Controller
@RequestMapping("")
@RestController
public class AsyncTaskController {
@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任務總耗時:"+(currentTimeMillis1-currentTimeMillis)+"ms";
}
}
異步任務類
@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任務耗時:"+(currentTimeMillis1-currentTimeMillis)+"ms");
}
@Async
public void task2() throws InterruptedException{
long currentTimeMillis = System.currentTimeMillis();
Thread.sleep(2000);
long currentTimeMillis1 = System.currentTimeMillis();
System.out.println("task2任務耗時:"+(currentTimeMillis1-currentTimeMillis)+"ms");
}
@Async
public void task3() throws InterruptedException{
long currentTimeMillis = System.currentTimeMillis();
Thread.sleep(3000);
long currentTimeMillis1 = System.currentTimeMillis();
System.out.println("task3任務耗時:"+(currentTimeMillis1-currentTimeMillis)+"ms");
}
}
控制檯:
task1任務耗時:1012ms
task2任務耗時:2009ms
task3任務耗時:3004ms
訪問瀏覽器結果入下:
task任務總耗時:19ms
異步調用成功!
如何知道三個異步任務什麼時候執行完,執行的結果怎樣呢?可以採用添加Fature回調方式判斷
代碼入下:
異步任務類
@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任務耗時:"+(currentTimeMillis1-currentTimeMillis)+"ms");
return new AsyncResult<String>("task1執行完畢");
}
@Async
public Future<String> task2() throws InterruptedException{
long currentTimeMillis = System.currentTimeMillis();
Thread.sleep(2000);
long currentTimeMillis1 = System.currentTimeMillis();
System.out.println("task2任務耗時:"+(currentTimeMillis1-currentTimeMillis)+"ms");
return new AsyncResult<String>("task2執行完畢");
}
@Async
public Future<String> task3() throws InterruptedException{
long currentTimeMillis = System.currentTimeMillis();
Thread.sleep(3000);
long currentTimeMillis1 = System.currentTimeMillis();
System.out.println("task3任務耗時:"+(currentTimeMillis1-currentTimeMillis)+"ms");
return new AsyncResult<String>("task3執行完畢");
}
}
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()) {
// 三個任務都調用完成,退出循環等待
break;
}
Thread.sleep(1000);
}
long currentTimeMillis1 = System.currentTimeMillis();
result = "task任務總耗時:"+(currentTimeMillis1-currentTimeMillis)+"ms";
return result;
}
}
控制檯輸出:
task1任務耗時:1000ms
task2任務耗時:2001ms
task3任務耗時:3001ms
瀏覽器輸出:
task任務總耗時:4015ms
異步調用成功,並且在所有任務都完成時程序才返回了結果!