背景

需要把一些调用其它服务器的执行时间比较长的方法异步化，这样就不要等待这些方法执行完后才执行其它的方法的。可以转换为异步方法的条件是

1. 它没有返回值，或者有返回值但是返回值和接下来要执行的代码没有关系。

2. 它的错误和调用它的方法没有关系，或者说它的错误它自己可以处理。

1. Maven 中依赖

     <parent><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-parent</artifactId><version>2.6.2</version><relativePath/></parent><dependencies><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-web</artifactId></dependency></dependencies>

1. 开启异步线程

在SpringBoot的启动类上面加上@EnableAsync

@SpringBootApplication
@Import(value = SpringAsyncConfig.class)
public class SpringBootClient {public static void main(String[] args) {SpringApplication.run( SpringBootClient.class, args );}
}

java异步调用方法。

2.  实例化自己的线程池

虽然SpringBoot已经帮我们做了默认配置，但是为了要掌握具体的内容还是可以自定义配置

@Configuration
@EnableAsync
public class SpringAsyncConfig implements AsyncConfigurer  {@Bean(name = "threadPoolTaskExecutor")public Executor threadPoolTaskExecutor() {return new ThreadPoolTaskExecutor();}public AsyncUncaughtExceptionHandler getAsyncUncaughtExceptionHandler() {return new CustomAsyncExceptionHandler();}
}

3. 还有自定义错误处理类

public class CustomAsyncExceptionHandler implements AsyncUncaughtExceptionHandler {@Overridepublic void handleUncaughtException(Throwable throwable, Method method, Object... obj) {System.out.println("Exception message - " + throwable.getMessage());System.out.println("Method name - " + method.getName());for (Object param : obj) {System.out.println("Parameter value - " + param);}}}

4. 异步方法的使用

asyncMethodWithVoidReturnType方法：不返回值

java异步返回结果、asyncMethodWithReturnType方法：有返回值

@Component
public class AsyncAnnotationExample {@Asyncpublic void asyncMethodWithVoidReturnType() {System.out.println("Execute method asynchronously. " + Thread.currentThread().getName());System.out.println(1/0);}@Asyncpublic Future<String> asyncMethodWithReturnType() {System.out.println("Execute method asynchronously - " + Thread.currentThread().getName());try {Thread.sleep(5000);return new AsyncResult<String>("hello world !!!!");} catch (InterruptedException e) {//}return null;}}

5. 写个Controller类做测试

test1接口测试有返回的异步方法

test2接口测试无返回的异步方法。

@RestController
public class AsyncController {@Autowiredprivate AsyncAnnotationExample asyncAnnotationExample;@RequestMapping("/test1")public String test1() {try {System.out.println("Invoking an asynchronous method. " + Thread.currentThread().getName());Future<String> future = asyncAnnotationExample.asyncMethodWithReturnType();while (true) {if (future.isDone()) {System.out.println("Result from asynchronous process - " + future.get());break;}System.out.println("Continue doing something else. ");Thread.sleep(1000);}}catch(Exception e) {e.printStackTrace();}return "test1";}@RequestMapping("/test2")public String test2() {System.out.println("Invoking an asynchronous method. " + Thread.currentThread().getName());asyncAnnotationExample.asyncMethodWithVoidReturnType();return "test2";}}