Question

我使用spring mvc 3.2.4和jquery 1.9.0进行长轮询。我的应用程序部署在Tomcat 7.0.42上。我的弹簧配置文件如下：

Application Web.xml

<web-app xmlns="http://java.sun.com/xml/ns/javaee"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://java.sun.com/xml/ns/javaee"   
  version="3.0">

    <welcome-file-list>
        <welcome-file>index.html</welcome-file>
    </welcome-file-list>

    <servlet>
        <servlet-name>app</servlet-name>

        <servlet-class>
            org.springframework.web.servlet.DispatcherServlet
        </servlet-class>

        <load-on-startup>1</load-on-startup>
        <async-supported>true</async-supported>
    </servlet>

    <servlet-mapping>
        <servlet-name>app</servlet-name>
        <url-pattern>/</url-pattern>
    </servlet-mapping>

    <listener>
        <listener-class>
            org.springframework.web.context.ContextLoaderListener
        </listener-class>
    </listener>

    <context-param>
        <param-name>contextConfigLocation</param-name>
        <param-value>
            /WEB-INF/app-servlet.xml
        </param-value>
    </context-param>

</web-app>

Spring Configration xml as： -

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:p="http://www.springframework.org/schema/p"
    xmlns:mvc="http://www.springframework.org/schema/mvc"
    xmlns:context="http://www.springframework.org/schema/context"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
    http://www.springframework.org/schema/beans/spring-beans-3.2.xsd
    http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc-3.2.xsd
    http://www.springframework.org/schema/context
    http://www.springframework.org/schema/context/spring-context-3.2.xsd">
        <context:annotation-config/>
        <mvc:annotation-driven/>  
        <mvc:default-servlet-handler/>
        <context:component-scan base-package="com.webchat"/>
        <bean id="defferedResult" class="com.exp.DeferredResultContainer"></bean>
</beans>

发布数据的控制器显示为

@RequestMapping(value = "/postComment", method = RequestMethod.POST)
public @ResponseBody String postComment(HttpServletRequest request) {
    deferredResultContainer.updateAllResults(request.getParameter("comment"));
    return "success";
}

延迟结果容器类

public class DeferredResultContainer {
    private final Set<DeferredResult<String>> deferredResults =   Collections.synchronizedSet(new HashSet<DeferredResult<String>>() ); 

    public void put(DeferredResult<String> deferredResult){ 
        deferredResults.add(deferredResult); 
    } 

    public void updateAllResults(String value){
        for (DeferredResult<String> deferredResult : deferredResults){ 
            deferredResult.setResult(value); 
        }
    }

    public void remove(DeferredResult<String> deferredResult){ 
        deferredResults.remove(deferredResult); 
    } 

    public int determineSize(){
        return deferredResults.size();
    }
}

延迟结果的控制器显示为

 @RequestMapping(value = "/getComments", method = RequestMethod.GET)
 @ResponseBody
 public DeferredResult<String> getComments() throws Exception{
     final DeferredResult<String> deferredResult= new DeferredResult<String>(); 
     deferredResultContainer.put(deferredResult);
     deferredResult.onTimeout(new Runnable() {

         @Override public void run() {
             deferredResultContainer.remove(deferredResult);
         }
     });

     deferredResult.onCompletion(new Runnable() { 
         @Override public void run() { 
             deferredResultContainer.remove(deferredResult); 
         } 
     });
     return deferredResult;
 }

当我试图通过ajax进行长时间轮询时，我得到了以下回复： -

{"setOrExpired":false}

onCompletion方法也没有被执行。

简单到控制器下面的东西给出了完美的响应 { “1”： “2”}

@RequestMapping(value = "/test1", method = RequestMethod.GET)
@ResponseBody
public Map test1() throws Exception{
     Map m1 = new HashMap<String, Object>();
     m1.put("1", "2");
     return m1;
}

一旦我将其更改为下面并添加延迟结果，我得到响应 { “setOrExpired”：真}

@RequestMapping(value = "/test", method = RequestMethod.GET)
@ResponseBody
public DeferredResult<Map> test() throws Exception{
    DeferredResult<Map> result = new DeferredResult<Map>();
     Map m1 = new HashMap<String, Object>();
     m1.put("1", "2");
     result.setResult(m1);
     return result;
}

轮询代码

$(document).ready(function() {
    longPoll();

    function longPoll(){
         $.support.cors = true;
        var path = "http://localhost:8080/WebChatExp/rest";
         $.ajax({
            url: path + "/getComments",
            cache:false,
            success: function(data){
                //To Do
                            alert("Data" + JSON.stringify(data));
            },
            error: function(err, status, errorThrown ) {

            },
            type: "GET",
            dataType: "json",
            complete: longPoll,
            timeout: 60000 // timeout every one minute
        }); 
    }

我搜索了各种示例，但无法确定延迟结果是否需要任何额外配置。请指教。

Answer 1

您正在获得的回复正文

{"setOrExpired":true}

表示Spring将您的DeferredResult（包含setOrExpired的各种属性）序列化为JSON，而不是使用DeferredResultMethodReturnValueHandler处理它。换句话说，它使用另一个HandlerMethodReturnValueHandler，最有可能RequestResponseBodyMethodProcessor（处理@ResponseBody）来处理从@RequestMapping带注释的处理程序方法返回的值。（测试此方法的最简单方法是查看删除@ResponseBody注释时会发生什么。）

查看注册默认HandlerMethodReturnValueHandler个实例的3.2.x source code of RequestMappingHandlerAdapter，DeferredResultMethodReturnValueHandler在RequestResponseBodyMethodProcessor之前注册，因此将首先处理DeferredResult返回值

由于您看到不同的行为，我们必须假设您的配置不是您在此处显示的内容。（请注意，<mvc:annotation-driven/>注册RequestMappingHandlerAdapter。）

另请注意，您目前正在/WEB-INF/app-servlet.xml两次加载配置，一次加载ContextLoaderListener，一次加载DispatcherServlet。

完全摆脱您的ContextLoaderListener和相应的context-param。在你的例子中不需要它们。

Answer 2

我知道在这种情况下（spring mvc 3.2.4）不可能是问题，只是为了将来参考：我在Spring Boot 2.2.0.BUILD-SNAPSHOT（spring 5.1.5）中遇到了同样的问题。当您尝试使用webflux而不是传统的spring mvc应用返回DeferredResult时，会发生此错误。请记住，在新的webflux api中，您应该使用mono / flux，而不是DeferredResult。

Spring MVC中的延迟结果返回错误响应

2 个答案: