Spring @Async

在Spring中可以使用@Async注解标记类或方法，有@Async注解的类会生成代理对象，代理对象会将有@Async注解的方法(异步方法)放在线程池里面异步执行；

@Async注解的方法返回值类型可以是void，也可以是Future类型，如果是普通类型则获取不到异步执行结果；

Spring默认使用的SimpleAsyncTaskExecutor线程池不会重用线程，并且没有最大线程数的限制，在大并发量的时候存在性能问题，所以Spring使用自定义线程池配合@Async注解一起使用；

一简单使用

在配置类中添加@EnableAsync注解；

在业务类中需要异步执行的方法上添加@Async注解；

1.1 方法返回值类型是void

@Configuration
@EnableAsync
public class CommonConfig {

}

@Service
public class OrderService {
    public void printOrderMsgOne() {
        try {
            // 模拟线程任务执行
            Thread.sleep(300);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("\t" + Thread.currentThread().getName()
                + " 输出message one...");
    }

    @Async
    public void printOrderMsgTwo() {
        try {
            // 模拟线程任务执行
            Thread.sleep(10000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("\t" + Thread.currentThread().getName()
                + " 输出message two...");
    }
}

@RestController
@RequestMapping("/order")
public class OrderController {
    @Autowired
    private OrderService orderService;

    @GetMapping("/one")
    public String orderOne() {
        System.out.println(Thread.currentThread().getName()
                + " 线程开始执行任务...");
        System.out.println("输出printOrderMsgOne方法信息: ");
        orderService.printOrderMsgOne();
        System.out.println("输出printOrderMsgTwo方法信息: ");
        orderService.printOrderMsgTwo();
        // 模拟线程任务执行
        try {
            Thread.sleep(3000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println(Thread.currentThread().getName()
                + " 线程结束执行任务...");
        return "success";
    }

}

方法执行结果：

http-nio-8081-exec-2 线程开始执行任务...
输出printOrderMsgOne方法信息:
http-nio-8081-exec-2 输出message one...
输出printOrderMsgTwo方法信息:
http-nio-8081-exec-2 线程结束执行任务...
task-1 输出message two...

orderOne方法在http-nio-8081-exec-2线程中执行，printOrderMsgTwo方法在task-1个线程异步执行；

1.2 方法返回值类型是普通类型

@Configuration
@EnableAsync
public class CommonConfig {

}

@Service
public class OrderService {
    public void printOrderMsgOne() {
        try {
            // 模拟线程任务执行
            Thread.sleep(300);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("\t" + Thread.currentThread().getName()
                + " 输出message one...");
    }

    @Async
    public String printOrderMsgTwo() {
        try {
            // 模拟线程任务执行
            Thread.sleep(10000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("\t" + Thread.currentThread().getName()
                + " 输出message two...");
        return "printOrderMsgTwo successfully";
    }
}

@RestController
@RequestMapping("/order")
public class OrderController {
    @Autowired
    private OrderService orderService;

    @GetMapping("/one")
    public String orderOne() {
        System.out.println(Thread.currentThread().getName()
                + " 线程开始执行任务...");
        System.out.println("输出printOrderMsgOne方法信息: ");
        orderService.printOrderMsgOne();
        System.out.println("输出printOrderMsgTwo方法信息: ");
        String str = orderService.printOrderMsgTwo();
        // 模拟线程任务执行
        try {
            Thread.sleep(3000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("异步执行结果: " + str);
        System.out.println(Thread.currentThread().getName()
                + " 线程结束执行任务...");
        return "success";
    }

}

方法执行结果：

http-nio-8081-exec-1 线程开始执行任务...
输出printOrderMsgOne方法信息:
http-nio-8081-exec-1 输出message one...
输出printOrderMsgTwo方法信息:
异步执行结果: null
http-nio-8081-exec-1 线程结束执行任务...
task-1 输出message two...

在orderOne方法中获取不到printOrderMsgTwo方法异步执行的结果，无论printOrderMsgTwo方法在orderOne方法响应之前完成还是之后完成，都获取不到printOrderMsgTwo方法的异步执行结果；

1.3 方法返回值类型是Future

@Configuration
@EnableAsync
public class CommonConfig {

}

@Service
public class OrderService {
    public void printOrderMsgOne() {
        try {
            // 模拟线程任务执行
            Thread.sleep(300);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("\t" + Thread.currentThread().getName()
                + " 输出message one...");
    }

    @Async
    public Future<String> printOrderMsgTwo() {
        try {
            // 模拟线程任务执行
            Thread.sleep(10000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("\t" + Thread.currentThread().getName()
                + " 输出message two...");
        return new AsyncResult<>("printOrderMsgTwo successfully");
    }
}

@RestController
@RequestMapping("/order")
public class OrderController {
    @Autowired
    private OrderService orderService;

    @GetMapping("/one")
    public String orderOne() {
        System.out.println(Thread.currentThread().getName()
                + " 线程开始执行任务...");
        System.out.println("输出printOrderMsgOne方法信息: ");
        orderService.printOrderMsgOne();
        System.out.println("输出printOrderMsgTwo方法信息: ");
        Future<String> future = orderService.printOrderMsgTwo();
        // 模拟线程任务执行
        try {
            Thread.sleep(3000);
            String str = future.get();
            System.out.println("异步执行结果: " + str);
        } catch (InterruptedException | ExecutionException e) {
            e.printStackTrace();
        }
        System.out.println(Thread.currentThread().getName()
                + " 线程结束执行任务...");
        return "success";
    }

}

方法执行结果：

http-nio-8081-exec-2 线程开始执行任务...
输出printOrderMsgOne方法信息:
http-nio-8081-exec-2 输出message one...
输出printOrderMsgTwo方法信息:
task-2 输出message two...
异步执行结果: printOrderMsgTwo successfully
http-nio-8081-exec-2 线程结束执行任务...

orderOne方法在http-nio-8081-exec-2线程中执行，printOrderMsgTwo在task-2线程中执行；

printOrderMsgTwo的方法返回值类型是Future，Future中的get方法是阻塞方法，所以orderOne方法会一直阻塞直到获得异步执行结果才会响应；

二自定义线程池

@Async注解的value属性用来指定使用具体的线程池

@Target({ElementType.TYPE, ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Async {
    String value() default "";
}

@Configuration
@EnableAsync
public class CommonConfig {

    @Bean("threadPoolOne")
    public ThreadPoolTaskExecutor threadPool() {
        ThreadPoolTaskExecutor threadPool = new ThreadPoolTaskExecutor();
        threadPool.setCorePoolSize(10);
        threadPool.setMaxPoolSize(15);
        threadPool.setQueueCapacity(15);
        threadPool.setKeepAliveSeconds(60);
        return threadPool;
    }

    @Bean("threadPoolTwo")
    public ThreadPoolTaskExecutor threadPoolTwo() {
        ThreadPoolTaskExecutor threadPool = new ThreadPoolTaskExecutor();
        threadPool.setCorePoolSize(10);
        threadPool.setMaxPoolSize(15);
        threadPool.setQueueCapacity(15);
        threadPool.setKeepAliveSeconds(60);
        return threadPool;
    }

}

@Service
public class OrderService {
    public void printOrderMsgOne() {
        try {
            // 模拟线程任务执行
            Thread.sleep(300);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("\t" + Thread.currentThread().getName()
                + " 输出message one...");
    }

    @Async("threadPoolTwo")
    public CompletableFuture<String> printOrderMsgTwo() {
        try {
            // 模拟线程任务执行
            Thread.sleep(10000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("\t" + Thread.currentThread().getName()
                + " 输出message two...");
        return CompletableFuture.completedFuture("printOrderMsgTwo successfully");
    }
}


@RestController
@RequestMapping("/order")
public class OrderController {
    @Autowired
    private OrderService orderService;

    @GetMapping("/one")
    public String orderOne() {
        System.out.println(Thread.currentThread().getName()
                + " 线程开始执行任务...");
        System.out.println("输出printOrderMsgOne方法信息: ");
        orderService.printOrderMsgOne();
        System.out.println("输出printOrderMsgTwo方法信息: ");
        CompletableFuture<String> future = orderService.printOrderMsgTwo();
        // 模拟线程任务执行
        try {
            Thread.sleep(3000);
            String str = future.get();
            System.out.println("异步执行结果: " + str);
        } catch (InterruptedException | ExecutionException e) {
            e.printStackTrace();
        }
        System.out.println(Thread.currentThread().getName()
                + " 线程结束执行任务...");
        return "success";
    }

}

方法执行结果：

http-nio-8081-exec-1 线程开始执行任务...
输出printOrderMsgOne方法信息:
http-nio-8081-exec-1 输出message one...
输出printOrderMsgTwo方法信息:
threadPoolTwo-1 输出message two...
异步执行结果: printOrderMsgTwo successfully
http-nio-8081-exec-1 线程结束执行任务...

orderOne方法用的是http-nio-8081-exec-1线程，printOrderMsgTwo方法用的threadPoolTwo线程池里面的线程；