目录：（可以按w快捷键切换大纲视图）
工程简介
2种异步example
- void没有返回值
- 有返回值
延伸阅读
spring boot 自带 @Async 注解，只要加到想要异步的方法上即可。有个小坑，就是只这样还是同步的service，还需要在main方法上加上 @EnableAsync 注解。
@SpringBootApplication
@EnableAsync
public class DemoApplication {
public static void main(String[] args) {
SpringApplication.run(DemoApplication.class, args);
}
}没有返回值的异步
service
@Service
public class AsyncNoReturnImpl implements AsyncNoReturn {
@Async
@Override
public void execAsync1(){
try{
Thread.sleep(2000);
System.out.println("甲睡了2000ms");
}catch (Exception e){
e.printStackTrace();
}
}
@Async
@Override
public void execAsync2(){
try{
Thread.sleep(4000);
System.out.println("乙睡了4000ms");
}catch (Exception e){
e.printStackTrace();
}
}
@Async
@Override
public void execAsync3(){
try{
Thread.sleep(3000);
System.out.println("丙睡了3000ms");
}catch (Exception e){
e.printStackTrace();
}
}
}controller
@GetMapping("/async-no-return")
public ResponseEntity<String> getAsyncNoReturn() {
long s = System.currentTimeMillis();
asyncNoReturn.execAsync1();
asyncNoReturn.execAsync2();
asyncNoReturn.execAsync3();
System.out.println("我执行结束了");
long costTime = System.currentTimeMillis() - s;
System.out.println("service async-no-return cost time: " + costTime);
return ResponseEntity.status(200).body("good");
}test
## async-no-return
GET http://localhost:8080/async-no-return
我执行结束了
service async-no-return cost time: 3
甲睡了2000ms
丙睡了3000ms
乙睡了4000ms
因为3个service都异步了，所以接口直接返回了，几乎没有花时间，3ms。3个service并行执行，4秒后全部执行完毕。
有返回值的异步
service
@Service
public class AsyncHasReturnImpl implements AsyncHasReturn {
@Async
public Future<String> execAsync1(){
try{
Thread.sleep(2000);
System.out.println("甲睡了2000ms");
return new AsyncResult<String>("甲执行成功了");
}catch (Exception e){
e.printStackTrace();
}
return null;
}
@Async
public Future<String> execAsync2(){
try{
Thread.sleep(4000);
System.out.println("乙睡了4000ms");
return new AsyncResult<String>("乙执行成功了");
}catch (Exception e){
e.printStackTrace();
}
return null;
}
@Async
public Future<String> execAsync3(){
try{
Thread.sleep(3000);
System.out.println("丙睡了3000ms");
return new AsyncResult<String>("丙执行结束了");
}catch (Exception e){
e.printStackTrace();
}
return null;
}
}controller
@GetMapping("/async-has-return")
public ResponseEntity<String> getAsyncHasReturn() throws ExecutionException, InterruptedException {
long s = System.currentTimeMillis();
Future<String> stringFuture1 = asyncHasReturn.execAsync1();
Future<String> stringFuture2 = asyncHasReturn.execAsync2();
Future<String> stringFuture3 = asyncHasReturn.execAsync3();
long costTime = System.currentTimeMillis() - s;
System.out.println("执行到代码中间了，cost time: " + costTime);
System.out.println("我执行结束了" + stringFuture1.get() + stringFuture2.get() + stringFuture3.get());
costTime = System.currentTimeMillis() - s;
System.out.println("service async-has-return cost time: " + costTime);
return ResponseEntity.status(200).body("good");
}test
## async-has-return
GET http://localhost:8080/async-has-return
执行到代码中间了，cost time: 1
甲睡了2000ms
丙睡了3000ms
乙睡了4000ms
我执行结束了甲执行成功了乙执行成功了丙执行结束了
service async-has-return cost time: 4006
可见将异步service赋值给Future是不花时间的，不需要等待当前异步线程执行完毕。只有get()方法需要等待当前的异步线程执行完毕，几个异步线程是并行执行的。类似get()方法的还有isDone()，因为get()已经包括了isDone()，所以不需要使用isDone()做判断了。
全部代码在： https://github.com/backendcloud/example/tree/master/spring-boot/async/demo/
转载请注明来源，欢迎指出任何有错误或不够清晰的表达。可以邮件至 backendcloud@gmail.com
