云时代架构Spring Cloud Java编程

SpringBoot系列之异步任务@Async使用教程

2020-07-20  本文已影响0人  smileNicky

@TOC

例子翻译自国外的两篇博客：

实验环境准备

创建一个SpringBoot Initialize项目，详情可以参考我之前博客：SpringBoot系列之快速创建项目教程

pom.xml：

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.2.1.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.example.springboot</groupId>
    <artifactId>springboot-async</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>springboot-async</name>
    <description>Demo project for Spring Boot</description>

    <properties>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
            <exclusions>
                <exclusion>
                    <groupId>org.junit.vintage</groupId>
                    <artifactId>junit-vintage-engine</artifactId>
                </exclusion>
            </exclusions>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

github用户信息类

@JsonIgnoreProperties(ignoreUnknown = true)，将这个注解写在类上之后，就会忽略类中不存在的字段，可以满足当前的需要。

package com.example.springboot.async.bean;

import com.fasterxml.jackson.annotation.JsonIgnore;
import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
import lombok.Data;

import java.io.Serializable;

/**
 * <pre>
 *  用户信息实体类
 *  Copy @ https://spring.io/guides/gs/async-method/
 * </pre>
 *
 * <pre>
 * 修改记录
 *    修改后版本:     修改人：  修改日期: 2020/07/20 10:14  修改内容:
 * </pre>
 */
@JsonIgnoreProperties(ignoreUnknown = true)
@Data
public class User implements Serializable {

    private String name;
    private String blog;

    @Override
    public String toString() {
        return "User{" +
                "name='" + name + '\'' +
                ", blog='" + blog + '\'' +
                '}';
    }
}

异步任务配置类

可以实现AsyncConfigurerSupport 类，也可以使用@Bean(name = "threadPoolTaskExecutor")的方法，这里定义了线程池的配置

package com.example.springboot.async.config;

import com.example.springboot.async.exception.CustomAsyncExceptionHandler;
import org.springframework.aop.interceptor.AsyncUncaughtExceptionHandler;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.scheduling.annotation.AsyncConfigurer;
import org.springframework.scheduling.annotation.AsyncConfigurerSupport;
import org.springframework.scheduling.annotation.EnableAsync;
import org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor;

import java.util.concurrent.Executor;

/**
 * <pre>
 *  AsyncConfiguration
 *  Copy @https://spring.io/guides/gs/async-method/
 * </pre>
 *
 * <pre>
 * 修改记录
 *    修改后版本:     修改人：  修改日期: 2020/07/20 10:12  修改内容:
 * </pre>
 */
@Configuration
@EnableAsync
public class AsyncConfiguration extends AsyncConfigurerSupport  {

    @Override
    public Executor getAsyncExecutor() {
        ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
        executor.setCorePoolSize(2);
        executor.setMaxPoolSize(2);
        executor.setQueueCapacity(500);
        executor.setThreadNamePrefix("GithubLookup-");
        executor.initialize();
        return executor;
    }

    /*@Bean(name = "threadPoolTaskExecutor")
    public Executor threadPoolTaskExecutor() {
        return new ThreadPoolTaskExecutor();
    }*/

  
}

查询github用户信息业务类

使用Future获得异步执行结果时，要么调用阻塞方法get()，要么轮询看isDone()是否为true，这两种方法都不是很好，因为主线程也会被迫等待。

在Java8中，CompletableFuture提供了非常强大的Future的扩展功能，可以帮助我们简化异步编程的复杂性，并且提供了函数式编程的能力，可以通过回调的方式处理计算结果，也提供了转换和组合 CompletableFuture 的方法。

package com.example.springboot.async.service;

import com.example.springboot.async.bean.User;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.boot.web.client.RestTemplateBuilder;
import org.springframework.scheduling.annotation.Async;
import org.springframework.stereotype.Service;
import org.springframework.web.client.RestTemplate;

import java.util.concurrent.CompletableFuture;
import java.util.concurrent.Future;

/**
 * <pre>
 *  GitHubLookupService
 * copy @https://spring.io/guides/gs/async-method/
 * </pre>
 *
 * <pre>
 * 修改记录
 *    修改后版本:     修改人：  修改日期: 2020/07/20 10:18  修改内容:
 * </pre>
 */
@Service
public class GitHubLookupService {

    private static final Logger LOG = LoggerFactory.getLogger(GitHubLookupService.class);

    private final RestTemplate restTemplate;

    public GitHubLookupService(RestTemplateBuilder restTemplateBuilder) {
        this.restTemplate = restTemplateBuilder.build();
    }

    @Async
    //@Async("threadPoolTaskExecutor")
    public Future<User> findUser(String user) throws InterruptedException {
        LOG.info("Looking up " + user);
        String url = String.format("https://api.github.com/users/%s", user);
        User results = restTemplate.getForObject(url, User.class);
        // Artificial delay of 1s for demonstration purposes
        Thread.sleep(1000L);
        return CompletableFuture.completedFuture(results);
    }

}

启动测试类实现

实现CommandLineRunner 接口，SpringBoot启动时候，会自动调用，也可以用@Order指定执行顺序

package com.example.springboot.async.service;

import com.example.springboot.async.bean.User;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.CommandLineRunner;
import org.springframework.stereotype.Component;

import java.util.concurrent.Future;

/**
 * <pre>
 *  CommandLineRunner
 *  Copy @https://spring.io/guides/gs/async-method/
 * </pre>
 *
 * <pre>
 * 修改记录
 *    修改后版本:     修改人：  修改日期: 2020/07/20 10:25  修改内容:
 * </pre>
 */
@Component
public class AppRunner implements CommandLineRunner {

    private static final Logger logger = LoggerFactory.getLogger(AppRunner.class);

    @Autowired
    GitHubLookupService gitHubLookupService;

    @Override
    public void run(String... args) throws Exception {
        // Start the clock
        long start = System.currentTimeMillis();

        // Kick of multiple, asynchronous lookups
        Future<User> page1 = gitHubLookupService.findUser("PivotalSoftware");
        Future<User> page2 = gitHubLookupService.findUser("CloudFoundry");
        Future<User> page3 = gitHubLookupService.findUser("Spring-Projects");

        // Wait until they are all done
        while (!(page1.isDone() && page2.isDone() && page3.isDone())) {
            Thread.sleep(10); //10-millisecond pause between each check
        }

        // Print results, including elapsed time
        logger.info("Elapsed time: " + (System.currentTimeMillis() - start));
        logger.info("--> " + page1.get());
        logger.info("--> " + page2.get());
        logger.info("--> " + page3.get());
    }
}

自定义异步任务异常

当方法返回类型为Future时，异常处理很容易– Future.get（）方法将引发异常。但是，如果返回类型为void，则异常不会传播到调用线程。因此，我们需要添加额外的配置来处理异常。我们将通过实现AsyncUncaughtExceptionHandler接口来创建自定义异步异常处理程序。

package com.example.springboot.async.exception;

import org.springframework.aop.interceptor.AsyncUncaughtExceptionHandler;

import java.lang.reflect.Method;

/**
 * <pre>
 *  Copy @ https://www.baeldung.com/spring-async
 * </pre>
 *
 * <pre>
 * 修改记录
 *    修改后版本:     修改人：  修改日期: 2020/07/20 11:08  修改内容:
 * </pre>
 */
public class CustomAsyncExceptionHandler implements AsyncUncaughtExceptionHandler  {

    @Override
    public 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);
        }
    }
}

需要重写getAsyncUncaughtExceptionHandler（）方法以返回我们的自定义异步异常处理程序

@Configuration
@EnableAsync
public class AsyncConfiguration extends AsyncConfigurerSupport  {

    // ...

    @Override
    public AsyncUncaughtExceptionHandler getAsyncUncaughtExceptionHandler() {
        return new CustomAsyncExceptionHandler();
    }
}

启动之后，可以看到如下信息，因为是多线程方式，所以都不是在main线程里的，异步执行的


在这里插入图片描述

如果注释@Async注解，再次启动，会发现都在main主线程里执行程序


在这里插入图片描述

代码例子下载：code download

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