SpringBoot非官方教程，异步方法

这篇文章主要介绍在springboot 使用异步方法，去请求github api.

创建工程

在pom文件引入相关依赖：

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

<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-web</artifactId>
</dependency>
<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-databind</artifactId>
</dependency>

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创建一个接收数据的实体：

@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 + "]";
}

}

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创建一个请求的　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<User> 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);
}

}

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通过，RestTemplate去请求，另外加上类@Async 表明是一个异步任务。

开启异步任务：

@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;
}

}

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通过@EnableAsync开启异步任务；并且配置AsyncConfigurerSupport，比如最大的线程池为2.

测试

测试代码如下：

@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<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());
}

}

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启动程序，控制台会打印：

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

耗时：3908

分析：可以卡的前面2个方法分别在GithubLookup-1 和GithubLookup-2执行，第三个在GithubLookup-2执行，注意因为在配置线程池的时候最大线程为2.如果你把线程池的个数为3的时候，耗时减少。

如果去掉@Async，你会发现，执行这三个方法都在main线程中执行。耗时总结，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

耗时：5261

通过这一个小的栗子，你应该对异步任务有了一定的了解。

参考资料

https://spring.io/guides/gs/async-method/

源码下载

https://github.com/forezp/SpringBootLearning