SpringMVC异步处理

- 日理万妓 2022-12-12 01:57 195阅读 0赞

> [https://en.wikipedia.org/wiki/Jakarta\_Servlet][https_en.wikipedia.org_wiki_Jakarta_Servlet]

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# 1 Servlet 3.0 异步处理 #

>  *  [https://www.jcp.org/en/home/inde][https_www.jcp.org_en_home_inde]
>  *  [https://download.oracle.com/otn-pub/jcp/servlet-3.0-mrel-eval-oth-JSpec/servlet-3\_0-mrel-spec.pdf][https_download.oracle.com_otn-pub_jcp_servlet-3.0-mrel-eval-oth-JSpec_servlet-3_0-mrel-spec.pdf]

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQwNzk0OTcz_size_16_color_FFFFFF_t_70][]

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQwNzk0OTcz_size_16_color_FFFFFF_t_70 1][]

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQwNzk0OTcz_size_16_color_FFFFFF_t_70 2][]

## 1.1 同步请求流程 ##

在Servlet 3.0之前，Servlet采用Thread-Per-Request的方式处理请求。即每一次Http请求都由某一个线程从头到尾负责处理。

如果一个请求需要进行IO操作，比如访问数据库、调用第三方服务接口等，那么其所对应的线程将同步地等待IO操作完成， 而IO操作是非常慢的，所以此时的线程并不能及时地释放回线程池以供后续使用，在并发量越来越大的情况下，这将带来严重的性能问题。即便是像Spring、Struts这样的高层框架也脱离不了这样的桎梏，因为他们都是建立在Servlet之上的。为了解决这样的问题，Servlet 3.0引入了异步处理，然后在Servlet 3.1中又引入了非阻塞IO来进一步增强异步处理的性能。

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQwNzk0OTcz_size_16_color_FFFFFF_t_70 3][]

## 1.2 异步请求流程  ##

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQwNzk0OTcz_size_16_color_FFFFFF_t_70 4][]

/**
     * 1.开启异步处理 asyncSupported=true
     */
    // http://localhost:8080/async
    @WebServlet(value = "/async", asyncSupported = true)
    public class AsyncServlet extends HttpServlet {
        private final HelloService helloService = new HelloService();
        @Override
        protected void doGet(HttpServletRequest req, HttpServletResponse resp) {
            System.out.println("thread name is " + Thread.currentThread().getName());
            System.out.println("doGet start timestamp=" + System.currentTimeMillis());
            //2.开启异步模式
            AsyncContext asyncContext = req.startAsync();
            //3.业务逻辑进行异步处理（开始）
            asyncContext.start(() -> {
                System.out.println("runnable start timestamp=" + System.currentTimeMillis());
                try {
                    String res = helloService.sayHello();
                    // 异步处理调用结束
                    asyncContext.complete();
                    //获取到异步的上下文
                    //AsyncContext async = req.getAsyncContext();
                    //4.获取响应
                    ServletResponse response = asyncContext.getResponse();
                    response.getWriter().write(res);
                    System.out.println("runnable end timestamp=" + System.currentTimeMillis());
                } catch (IOException ignored) {}
            });
            System.out.println("doGet end timestamp=" + System.currentTimeMillis());
        }
    }

public class HelloService {
        public String sayHello() {
            System.out.println("exe sayHello thread name is " + Thread.currentThread().getName());
            try {
                TimeUnit.SECONDS.sleep(3);
            } catch (InterruptedException ignored) {}
            return Thread.currentThread().getName();
        }
    }

<dependency>
        <groupId>javax.servlet</groupId>
        <artifactId>javax.servlet-api</artifactId>
        <version>4.0.1</version>
        <scope>provided</scope>
    </dependency>

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# 2 SpringMVC异步处理 #

>  *  [https://docs.spring.io/spring-framework/docs/5.0.2.RELEASE/spring-framework-reference/web.html\#mvc-ann-async-processing][https_docs.spring.io_spring-framework_docs_5.0.2.RELEASE_spring-framework-reference_web.html_mvc-ann-async-processing]
>  *  [https://docs.spring.io/spring-framework/docs/current/spring-framework-reference/web.html\#mvc-ann-async][https_docs.spring.io_spring-framework_docs_current_spring-framework-reference_web.html_mvc-ann-async]

[https_en.wikipedia.org_wiki_Jakarta_Servlet]: https://en.wikipedia.org/wiki/Jakarta_Servlet
[https_www.jcp.org_en_home_inde]: https://www.jcp.org/en/home/inde
[https_download.oracle.com_otn-pub_jcp_servlet-3.0-mrel-eval-oth-JSpec_servlet-3_0-mrel-spec.pdf]: https://download.oracle.com/otn-pub/jcp/servlet-3.0-mrel-eval-oth-JSpec/servlet-3_0-mrel-spec.pdf
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQwNzk0OTcz_size_16_color_FFFFFF_t_70]: /images/20221123/eb744cffbec84e4fb078e7875a91cd06.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQwNzk0OTcz_size_16_color_FFFFFF_t_70 1]: /images/20221123/5ff31fc2920d4cfb9c8e7f855a85383b.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQwNzk0OTcz_size_16_color_FFFFFF_t_70 2]: /images/20221123/5f424e8d011c4b2f9cddbe07c7d308e1.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQwNzk0OTcz_size_16_color_FFFFFF_t_70 3]: /images/20221123/93349a9a3c34439d9adb3f1cec3049bd.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQwNzk0OTcz_size_16_color_FFFFFF_t_70 4]: /images/20221123/d1a932b984184ece9b7370672d47f37f.png
[https_docs.spring.io_spring-framework_docs_5.0.2.RELEASE_spring-framework-reference_web.html_mvc-ann-async-processing]: https://docs.spring.io/spring-framework/docs/5.0.2.RELEASE/spring-framework-reference/web.html#mvc-ann-async-processing
[https_docs.spring.io_spring-framework_docs_current_spring-framework-reference_web.html_mvc-ann-async]: https://docs.spring.io/spring-framework/docs/current/spring-framework-reference/web.html#mvc-ann-async