Spring @Async實現異步調用示例

時間 2019-12-06

原文原文鏈接

什麼是「異步調用」？java

「異步調用」對應的是「同步調用」，同步調用指程序按照定義順序依次執行，每一行程序都必須等待上一行程序執行完成以後才能執行；異步調用指程序在順序執行時，不等待異步調用的語句返回結果就執行後面的程序。web

同步調用

下面經過一個簡單示例來直觀的理解什麼是同步調用：spring

定義Task類，建立三個處理函數分別模擬三個執行任務的操做，操做消耗時間隨機取（10秒內）併發

package com.dxz.demo1;

import java.util.Random;
import org.springframework.stereotype.Component;
import org.springframework.web.bind.annotation.RequestMapping;

/**
 * 定義3個任務
 */
@Component
public class Task1 {
    
    // 定義一個隨機對象.
    public static Random random = new Random();

    // 任務一;
    public void doTaskOne() throws Exception {
        System.out.println("開始作任務一");
        long start = System.currentTimeMillis();
        Thread.sleep(random.nextInt(10000));
        long end = System.currentTimeMillis();
        System.out.println("完成任務一，耗時：" + (end - start) + "毫秒");
    }

    // 任務二;
    public void doTaskTwo() throws Exception {
        System.out.println("開始作任務二");
        long start = System.currentTimeMillis();
        Thread.sleep(random.nextInt(10000));
        long end = System.currentTimeMillis();
        System.out.println("完成任務二，耗時：" + (end - start) + "毫秒");
    }

    // 任務3;
    public void doTaskThree() throws Exception {
        System.out.println("開始作任務三");
        long start = System.currentTimeMillis();
        Thread.sleep(random.nextInt(10000));
        long end = System.currentTimeMillis();
        System.out.println("完成任務三，耗時：" + (end - start) + "毫秒");
    }
    

}

編寫一個訪問方法：app

package com.dxz.demo1;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.SpringApplicationConfiguration;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;

import com.dxz.HelloApplication;

@RunWith(SpringJUnit4ClassRunner.class)
@SpringApplicationConfiguration(classes = HelloApplication.class)
public class Task1Test {

    @Autowired
    private Task1 task1;
    
    //測試task1.
    @Test
    public void task1() throws Exception{
       task1.doTaskOne();
       task1.doTaskTwo();
       task1.doTaskThree();
    }
}

運行能夠看到相似以下輸出：dom

開始作任務一
2017-04-28 18:02:57.397  WARN 11016 --- [cTaskExecutor-1] o.s.a.r.l.SimpleMessageListenerContainer : Consumer raised exception, processing can restart if the connection factory supports it. Exception summary: org.springframework.amqp.AmqpConnectException: java.net.ConnectException: Connection refused: connect
2017-04-28 18:02:57.398  INFO 11016 --- [cTaskExecutor-1] o.s.a.r.l.SimpleMessageListenerContainer : Restarting Consumer: tags=[{}], channel=null, acknowledgeMode=AUTO local queue size=0
完成任務一，耗時：7740毫秒
開始作任務二
完成任務二，耗時：723毫秒
開始作任務三
2017-04-28 18:03:03.415  WARN 11016 --- [cTaskExecutor-2] o.s.a.r.l.SimpleMessageListenerContainer : Consumer raised exception, processing can restart if the connection factory supports it. Exception summary: org.springframework.amqp.AmqpConnectException: java.net.ConnectException: Connection refused: connect
2017-04-28 18:03:03.415  INFO 11016 --- [cTaskExecutor-2] o.s.a.r.l.SimpleMessageListenerContainer : Restarting Consumer: tags=[{}], channel=null, acknowledgeMode=AUTO local queue size=0
完成任務三，耗時：5047毫秒

異步調用

上述的同步調用雖然順利的執行完了三個任務，可是能夠看到執行時間比較長，若這三個任務自己之間不存在依賴關係，能夠併發執行的話，同步調用在執行效率方面就比較差，能夠考慮經過異步調用的方式來併發執行。異步

在Spring Boot中，咱們只須要經過使用@Async註解就能簡單的將原來的同步函數變爲異步函數，Task類改在爲以下模式：函數

package com.dxz.demo1;

import java.util.Random;

import org.springframework.scheduling.annotation.Async;
import org.springframework.stereotype.Component;
import org.springframework.web.bind.annotation.RequestMapping;

/**
 * 定義3個任務
 */
@Component
public class Task2 {
    
    // 定義一個隨機對象.
    public static Random random = new Random();

    // 任務一;
    @Async
    public void doTaskOne() throws Exception {
        System.out.println("開始作任務一");
        long start = System.currentTimeMillis();
        Thread.sleep(random.nextInt(10000));
        long end = System.currentTimeMillis();
        System.out.println("完成任務一，耗時：" + (end - start) + "毫秒");
    }

    // 任務二;
    @Async
    public void doTaskTwo() throws Exception {
        System.out.println("開始作任務二");
        long start = System.currentTimeMillis();
        Thread.sleep(random.nextInt(10000));
        long end = System.currentTimeMillis();
        System.out.println("完成任務二，耗時：" + (end - start) + "毫秒");
    }

    // 任務3;
    @Async
    public void doTaskThree() throws Exception {
        System.out.println("開始作任務三");
        long start = System.currentTimeMillis();
        Thread.sleep(random.nextInt(10000));
        long end = System.currentTimeMillis();
        System.out.println("完成任務三，耗時：" + (end - start) + "毫秒");
    }
    

}

爲了讓@Async註解可以生效，還須要在Spring Boot的主程序中配置@EnableAsync，以下所示：單元測試

package com.dxz;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.scheduling.annotation.EnableAsync;
@EnableAsync
@SpringBootApplication
public class HelloApplication {
    public static void main(String[] args) {
        SpringApplication.run(HelloApplication.class, args);
    }
}

編寫測試方法：測試

package com.dxz.demo1;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.SpringApplicationConfiguration;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
import org.springframework.web.bind.annotation.RequestMapping;

import com.dxz.HelloApplication;

@RunWith(SpringJUnit4ClassRunner.class)
@SpringApplicationConfiguration(classes = HelloApplication.class)
public class Task2Test {

    @Autowired
    private Task2 task2;
    
    //測試task1.
    @Test
    public void task1() throws Exception{
       task2.doTaskOne();
       task2.doTaskTwo();
       task2.doTaskThree();
    }
}

此時能夠反覆執行單元測試，您可能會遇到各類不一樣的結果，好比：

開始作任務一
開始作任務二
開始作任務三

修改下測試類：

package com.dxz.demo1;

import java.util.concurrent.TimeUnit;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.SpringApplicationConfiguration;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
import org.springframework.web.bind.annotation.RequestMapping;

import com.dxz.HelloApplication;

@RunWith(SpringJUnit4ClassRunner.class)
@SpringApplicationConfiguration(classes = HelloApplication.class)
public class Task2Test {

    @Autowired
    private Task2 task2;

    // 測試task1.
    @Test
    public void task1() throws Exception {
        task2.doTaskOne();
        task2.doTaskTwo();
        task2.doTaskThree();

        System.out.println("i'm here");
        TimeUnit.SECONDS.sleep(15);
        System.out.println("over");
    }

}

jieguo:

i'm here開始作任務二開始作任務一開始作任務三完成任務三，耗時：1280毫秒2017-04-28 18:25:36.936 WARN 17848 --- [cTaskExecutor-1] o.s.a.r.l.SimpleMessageListenerContainer : Consumer raised exception, processing can restart if the connection factory supports it. Exception summary: org.springframework.amqp.AmqpConnectException: java.net.ConnectException: Connection refused: connect2017-04-28 18:25:36.938 INFO 17848 --- [cTaskExecutor-1] o.s.a.r.l.SimpleMessageListenerContainer : Restarting Consumer: tags=[{}], channel=null, acknowledgeMode=AUTO local queue size=0完成任務一，耗時：4951毫秒完成任務二，耗時：7451毫秒2017-04-28 18:25:42.971 WARN 17848 --- [cTaskExecutor-2] o.s.a.r.l.SimpleMessageListenerContainer : Consumer raised exception, processing can restart if the connection factory supports it. Exception summary: org.springframework.amqp.AmqpConnectException: java.net.ConnectException: Connection refused: connect2017-04-28 18:25:42.972 INFO 17848 --- [cTaskExecutor-2] o.s.a.r.l.SimpleMessageListenerContainer : Restarting Consumer: tags=[{}], channel=null, acknowledgeMode=AUTO local queue size=0over