从 CompletableFuture 线程中的主线程访问 SessionScoped bean 不起作用

Question

我是 Spring 引导开发的新手。我需要运行使用 CompletableFuture 并行执行一些任务，还需要从 CompletableFuture 线程中的主线程访问 SessionScoped bean。根据 blow 代码，当它尝试从 HelloService.completableFuture1() 调用 helloBean.getHelloMessage() 时，它会停止进一步处理。任何帮助将不胜感激。

SessionScopeWithCfApplication.java

@EnableAsync
@SpringBootApplication
public class SessionScopeWithCfApplication {

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

}

=====

HelloBean.java

public class HelloBean {

    private String helloMessage;

    public String getHelloMessage() {
        return helloMessage;
    }

    public void setHelloMessage(String helloMessage) {
        this.helloMessage = helloMessage;
    }


}

=====

HelloBeanScopeConfig.java

@Configuration
public class HelloBeanScopeConfig {

    @Bean
    //@SessionScope
    //@Scope(value = "session",  proxyMode = ScopedProxyMode.TARGET_CLASS)
    @Scope(value = WebApplicationContext.SCOPE_SESSION, proxyMode = ScopedProxyMode.TARGET_CLASS)
    public HelloBean helloBean() {
        return new HelloBean();
    }

}

=====

HelloController.java

@Controller
public class HelloController {

    @Resource(name = "helloBean")
    HelloBean helloBean;
    
    @RequestMapping(value = {"/"}, method = RequestMethod.GET)
    public String home(Model model, HttpServletRequest request) {
        System.out.println("HelloController.home() - helloBean.getHelloMessage() = " + helloBean.getHelloMessage());
        helloBean.setHelloMessage("Welcome");
        System.out.println("HelloController.home() - helloBean.getHelloMessage() = " + helloBean.getHelloMessage());
    return "index";
    }
    
}

=====

index.html

<!DOCTYPE html>
<html xmlns:th="http://www.thymeleaf.org"
      xmlns:sec="http://www.thymeleaf.org/thymeleaf-extras-springsecurity5">
<head>
    <meta charset="utf-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1" />
    <title>Login</title>
    <link rel="stylesheet" type="text/css" th:href="@{/webjars/bootstrap/3.3.6/css/bootstrap.min.css}" />
        <script type='text/javascript' th:src="@{/webjars/jquery/1.9.1/jquery.min.js}"></script>
    <script type="text/javascript" th:src="@{/webjars/bootstrap/3.3.6/js/bootstrap.min.js}"></script>
    <script type='text/javascript'>
        function getHelloMessage() {
            return $.ajax({
                url: '/gethellomessage',
                method: 'get',
                contentType: "application/json; charset=utf-8",
            });
        };
        $(document).ready(function() {
            $('#btn').on('click', function () {
                getHelloMessage();
            }); 
        });
    </script>
</head>
<body>
    <div>
        <button id="btn" type="submit" class="btn btn-primary">Click Me</button>
    </div>
</body>
</html>

=====

HelloRestController.java

@RestController
public class HelloRestController {

    @Autowired
    HelloService helloService;
    
    @Resource(name = "helloBean")
    HelloBean helloBean;
    
    @RequestMapping(value = "/gethellomessage", method = RequestMethod.GET)
    public ResponseEntity getHelloMessage() {
    try {
            System.out.println("HelloRestController.getHelloMessage() - helloBean.getHelloMessage() = " + helloBean.getHelloMessage());
            helloService.completableFuture1();
            //CompletableFuture.allOf(helloService.completableFuture1()).get();
            return new ResponseEntity(HttpStatus.OK);
    } catch (Exception e) {
            return ResponseEntity.status(HttpStatus.BAD_REQUEST).body(e.getMessage());
    }        
    }

}

=====

HelloService.java

@Service
public class HelloService {

    @Resource(name = "helloBean")
    HelloBean helloBean;

    @Async
    @Scope(value = WebApplicationContext.SCOPE_SESSION, proxyMode = ScopedProxyMode.TARGET_CLASS)
    public CompletableFuture<Void> completableFuture1() {
        System.out.println("executing completableFuture1 by - "+Thread.currentThread().getName());
    try {
            System.out.println("completableFuture1 - helloBean.getHelloMessage() = " + helloBean.getHelloMessage());
        Thread.sleep(5000);
            System.out.println("Done completableFuture1");
    } catch (Exception e) {
            throw new RuntimeException((new Exception().getStackTrace()[0].getMethodName()) + ": " + e.getClass().getSimpleName() + ": " + e.getMessage());
    }
        return CompletableFuture.completedFuture(null);
    }
    
}


Output:

HelloController.home() - helloBean.getHelloMessage() = null
HelloController.home() - helloBean.getHelloMessage() = Welcome
HelloRestController.getHelloMessage() - helloBean.getHelloMessage() = Welcome
executing completableFuture1 by - task-1

It is not printing value from HelloService.completableFuture1() for the below command and stops processing at this stage:
    
System.out.println("completableFuture1 - helloBean.getHelloMessage() = " + helloBean.getHelloMessage());

Answer 1

问题出在不正确的 bean 存储范围内，因为我收到以下异常消息：

No thread-bound request found: Are you referring to request attributes outside of
an actual web request, or processing a request outside of the originally receiving 
thread? If you are actually operating within a web request and still receive this 
message, your code is probably running outside of DispatcherServlet: In this case, 
use RequestContextListener or RequestContextFilter to expose the current request.

为什么会这样，所有带有请求、会话范围的 bean 都存储在 ThreadLocal classes 中。 bean存储很少，位于LocaleContextHolder和RequestContextHolder，这些上下文与DispatcherServlet相关，servlet将执行initContextHolders和[=21]的每个请求=].

当请求到达服务器时，服务器从池中提供线程并且DispatcherServlet开始在该线程中执行请求，该线程从http会话接收会话范围的bean并创建请求范围的bean的新实例，以及所有这些bean如果这些组件在与 DispatcherServlet.

相同的线程中执行，则在任何 spring 组件（控制器、服务）中都可用

在我们的例子中，我们从正在执行 DispatcherServlet 的线程（主）启动新线程，这意味着，bean 存储已经为新线程更改，它是从 @Async 代理启动的用于执行我们的方法，因为线程直接与 ThreadLocal class 连接，因此在新线程中没有会话范围的 bean。

我们可以通过将属性 setThreadContextInheritable 设置为 true 来设置 bean 存储的可继承性，方法如下：

@Configuration
public class WebConfig {

    @Bean
    @SessionScope
    public HelloBean helloBean() {
        return new HelloBean();
    }

    @Bean(name = DEFAULT_DISPATCHER_SERVLET_BEAN_NAME)
    public DispatcherServlet dispatcherServlet(WebMvcProperties webMvcProperties) {
        DispatcherServlet dispatcherServlet = new DispatcherServlet();
        dispatcherServlet.setThreadContextInheritable(true);
        dispatcherServlet.setDispatchOptionsRequest(webMvcProperties.isDispatchOptionsRequest());
        dispatcherServlet.setDispatchTraceRequest(webMvcProperties.isDispatchTraceRequest());
        dispatcherServlet.setThrowExceptionIfNoHandlerFound(webMvcProperties.isThrowExceptionIfNoHandlerFound());
        dispatcherServlet.setPublishEvents(webMvcProperties.isPublishRequestHandledEvents());
        dispatcherServlet.setEnableLoggingRequestDetails(webMvcProperties.isLogRequestDetails());
        return dispatcherServlet;
    }

}

然后稍微改变一下HelloService:

@Service
public class HelloService {

    @Autowired
    private HelloBean helloBean;

    @Async
    public CompletableFuture<Void> completableFuture1() {
        System.out.println("executing completableFuture1 by - " + Thread.currentThread().getName());
        try {
            System.out.println("completableFuture1 - helloBean.getHelloMessage() = " + helloBean.getHelloMessage());
            Thread.sleep(5000);
            System.out.println("Done completableFuture1");
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
        return CompletableFuture.completedFuture(null);
    }

}

设置后属性所有新线程将从父线程继承 bean 存储，因此您的会话作用域 bean 将可用。 警告： 属性您不能与线程池一起使用，请参阅 java 文档：

    /**
     * Set whether to expose the LocaleContext and RequestAttributes as inheritable
     * for child threads (using an {@link java.lang.InheritableThreadLocal}).
     * <p>Default is "false", to avoid side effects on spawned background threads.
     * Switch this to "true" to enable inheritance for custom child threads which
     * are spawned during request processing and only used for this request
     * (that is, ending after their initial task, without reuse of the thread).
     * <p><b>WARNING:</b> Do not use inheritance for child threads if you are
     * accessing a thread pool which is configured to potentially add new threads
     * on demand (e.g. a JDK {@link java.util.concurrent.ThreadPoolExecutor}),
     * since this will expose the inherited context to such a pooled thread.
     */
    public void setThreadContextInheritable(boolean threadContextInheritable) {
        this.threadContextInheritable = threadContextInheritable;
    }

P.S. 您可以更改代码段：

    @Resource(name = "helloBean")
    private HelloBean helloBean;

在

    @Autowired
    private HelloBean helloBean;

Spring 支持两种注入 bean 的方式，从我的角度来看，第二个代码片段更 spring 风格。

从 CompletableFuture 线程中的主线程访问 SessionScoped bean 不起作用

Accessing SessionScoped bean from main thread within the CompletableFuture thread is not working

java

multithreading

spring-boot

completable-future

session-scope