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>启动类：添加@EnableAsync注解
@SpringBootApplication
@EnableAsync // 启动异步调用
public class AsyncApplicationWithAnnotation {
private static final Logger log = LoggerFactory.getLogger(AsyncApplicationWithAnnotation.class);
/**
* 自定义异步线程池
* @return
*/
@Bean
public AsyncTaskExecutor taskExecutor() {
ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
executor.setThreadNamePrefix("Anno-Executor");
executor.setMaxPoolSize(10);
// 设置拒绝策略
executor.setRejectedExecutionHandler(new RejectedExecutionHandler() {
@Override
public void rejectedExecution(Runnable r, ThreadPoolExecutor executor) {
// .....
}
});
// 使用预定义的异常处理类
// executor.setRejectedExecutionHandler(new ThreadPoolExecutor.CallerRunsPolicy());
return executor;
}
public static void main(String[] args) {
log.info("Start AsyncApplication.. ");
SpringApplication.run(AsyncApplicationWithAnnotation.class, args);
}
}以上的异常方法和普通的方法调用相同
@RunWith(SpringRunner.class)
@SpringBootTest(classes=AsyncApplicationWithAnnotation.class)
public class AsyncApplicationWithAnnotationTests {
@Autowired
private AsyncDemo asyncDemo;
@Test
public void contextLoads() throws InterruptedException, ExecutionException {
asyncDemo.asyncInvokeSimplest();
asyncDemo.asyncInvokeWithParameter("test");
Future<String> future = asyncDemo.asyncInvokeReturnFuture(100);
System.out.println(future.get());
}
}@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");
}main函数运行spirngboot项目，启动完成后浏览器访问：
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
@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任务总耗时:"+(currentTimeMillis1-currentTimeMillis)+"ms";
}
}
异步任务类
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
@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：
-
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