摘要：如果去掉，你會發現，執行這三個方法都在線程中執行。耗時總結，如下耗時通過這一個小的栗子，你應該對異步任務有了一定的了解。

這篇文章主要介紹在springboot 使用異步方法，去請求github api.

在pom文件引入相關依賴：

    
        org.springframework.boot
        spring-boot-starter
    

    
        org.springframework
        spring-web
    
    
        com.fasterxml.jackson.core
        jackson-databind
    

創建一個接收數據的實體：

@JsonIgnoreProperties(ignoreUnknown=true)
public class User {

    private String name;
    private String blog;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getBlog() {
        return blog;
    }

    public void setBlog(String blog) {
        this.blog = blog;
    }

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

}

創建一個請求的　githib的service:

@Service
public class GitHubLookupService {

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

    private final RestTemplate restTemplate;

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

    @Async
    public Future findUser(String user) throws InterruptedException {
        logger.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 new AsyncResult<>(results);
    }

}

通過，RestTemplate去請求，另外加上類@Async 表明是一個異步任務。

開啟異步任務：

@SpringBootApplication
@EnableAsync
public class Application extends AsyncConfigurerSupport {

    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }

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

}

通過@EnableAsync開啟異步任務；并且配置AsyncConfigurerSupport，比如最大的線程池為2.

測試代碼如下：

@Component
public class AppRunner implements CommandLineRunner {

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

    private final GitHubLookupService gitHubLookupService;

    public AppRunner(GitHubLookupService gitHubLookupService) {
        this.gitHubLookupService = gitHubLookupService;
    }

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

        // Kick of multiple, asynchronous lookups
        Future page1 = gitHubLookupService.findUser("PivotalSoftware");
        Future page2 = gitHubLookupService.findUser("CloudFoundry");
        Future 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());
    }

}

啟動程序，控制臺會打印：

2017-04-30 13:11:10.351 INFO 1511 — [ GithubLookup-1] com.forezp.service.GitHubLookupService : Looking up PivotalSoftware
2017-04-30 13:11:10.351 INFO 1511 — [ GithubLookup-2] com.forezp.service.GitHubLookupService : Looking up CloudFoundry
2017-04-30 13:11:13.144 INFO 1511 — [ GithubLookup-2] com.forezp.service.GitHubLookupService : Looking up Spring-Projects

耗時：3908

分析：可以卡的前面2個方法分別在GithubLookup-1 和GithubLookup-2執行，第三個在GithubLookup-2執行，注意因為在配置線程池的時候最大線程為2.如果你把線程池的個數為3的時候，耗時減少。

如果去掉@Async，你會發現，執行這三個方法都在main線程中執行。耗時總結，如下：

2017-04-30 13:13:00.934 INFO 1527 — [ main] com.forezp.service.GitHubLookupService : Looking up PivotalSoftware
2017-04-30 13:13:03.571 INFO 1527 — [ main] com.forezp.service.GitHubLookupService : Looking up CloudFoundry
2017-04-30 13:13:04.865 INFO 1527 — [ main] com.forezp.service.GitHubLookupService : Looking up Spring-Projects

耗時：5261

通過這一個小的栗子，你應該對異步任務有了一定的了解。

https://spring.io/guides/gs/a...

https://github.com/forezp/Spr...