Spring 对异步调用提供了良好的支持，只需在启动类上添加注解 @EnableAsync，然后在要执行异步操作的类或方法上添加注解 @Async 即可。
开启异步调用
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| @EnableAsync
@SpringBootApplication
public class WebApplication {
public static void main(String[] args) {
SpringApplication.run(WebApplication.class, args);
}
}
|
创建异步任务
@Async 注解既可以添加在类上，也可以添加在方法上，如果是添加在类上，则该类下的所有方法都将被异步执行。
如果异步方法有返回值，则需要指定其返回对象类型为 Future。
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| @Slf4j
@Component
public class AsyncTask {
@Async
public void execute() {
log.info("Execution thread name: {}", Thread.currentThread().getName());
try {
TimeUnit.SECONDS.sleep(5);
} catch (InterruptedException e) {
log.error("Error!", e);
}
}
@Async
public Future<String> executeAndReturn() {
log.info("Execution thread name: {}", Thread.currentThread().getName());
try {
TimeUnit.SECONDS.sleep(5);
} catch (InterruptedException e) {
log.error("Error!", e);
}
return new AsyncResult<>("Hello world !");
}
}
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需要注意的是，由于对于 Spring 默认使用代理模式处理 @Async，因此同一类中的本地调用不会被拦截，即 @Async 将会被忽略。
调用异步任务
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| @Slf4j
@RequestMapping(("asyncCall"))
@RestController
public class AsyncCallController {
private final AsyncTask asyncTask;
public AsyncCallController(AsyncTask asyncTask) {
this.asyncTask = asyncTask;
}
@GetMapping("execute")
public void execute() {
log.info("Main thread name: {}", Thread.currentThread().getName());
asyncTask.execute();
}
@GetMapping("executeAndReturn")
public String executeAndReturn() throws ExecutionException, InterruptedException {
log.info("Main thread name: {}", Thread.currentThread().getName());
Future<String> future = asyncTask.executeAndReturn();
while (true) {
if (future.isDone()) {
return future.get();
} else {
log.info("Task is working");
TimeUnit.SECONDS.sleep(1);
}
}
}
}
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配置线程池
Spring 会调用由它管理的 Executor 来处理 @Async。如果没有配置 Executor，它会自己创建 SimpleAsyncTaskExecutor。我们可以通过配置参数来调整它的默认配置。
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| spring:
task:
execution:
pool:
core-size: 5
max-size: 10
queue-capacity: 200
keep-alive: 10s
thread-name-prefix: task-
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我们也可以自定义 Executor，只需要实现类 AsyncConfigurer 并在其方法 getAsyncExecutor() 中返回自定义的 Executor。
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| @Configuration
public class AsyncConfig implements AsyncConfigurer {
public static final String ASYNC_EXECUTOR_NAME = "taskExecutor";
private final TaskExecutionProperties properties;
public AsyncConfig(TaskExecutionProperties properties) {
this.properties = properties;
}
@Bean(ASYNC_EXECUTOR_NAME)
@Override
public Executor getAsyncExecutor() {
ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
executor.setCorePoolSize(properties.getPool().getCoreSize());
executor.setMaxPoolSize(properties.getPool().getMaxSize());
executor.setQueueCapacity(properties.getPool().getQueueCapacity());
executor.setKeepAliveSeconds((int) properties.getPool().getKeepAlive().getSeconds());
executor.setThreadNamePrefix(properties.getThreadNamePrefix());
executor.setTaskDecorator(new ContextCopyingDecorator());
executor.initialize();
return executor;
}
}
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如果需要同时配置多个线程池，可以配置多个 Executor Bean。（如果使用了 Spring MVC 中的异步请求，需求将 Executor 的类型设置为 AsyncTaskExecutor）
