Question

我使用Spring 4.0.5和Servlet API 3.1.0创建了一个异步MVC应用程序。使用Firefox 24，异步行为在Jetty 8.0中运行良好，但我无法在Tomcat 8.0和Firefox 24中使用它。我使用DeferredResult来管理异步请求。知道我错过了什么吗？它可能是一些Tomcat设置或web.xml中的某些内容，因为完全相同的Java代码在Jetty中运行良好。

当异步请求最终产生结果并且应该写入响应时，我看到记录了以下消息：

WebAsyncManager - Dispatching request to resume processing
RequestResponseBodyMethodProcessor - Written [true] as "application/json" using MappingJacksonHttpMessageConvertor
DispatcherServlet - Null ModelAndView returned to DispatcherServlet with name 'app': assuming HandlerAdapter completed request handling
DispatcherServlet - Successfully completed request

长时间运行的请求永远不会回到我的浏览器，最终我在Tomcat日志中看到这个超时错误：

CoyoteAdapter.asyncDispatch Exception while processing an asynchronous request
java.lang.IllegalStateException: Calling [asyncTimeout()] is not valid for a request with Async state [Dispatching]

- server.xml中 -

    <Connector port="8080" protocol="org.apache.coyote.http11.Http11NioProtocol" 
        maxConnections="100"
               maxThreads="100"
               connectionTimeout="150000" 
               asyncTimeout="150000" />

- Tomcat web.xml -

<?xml version="1.0" encoding="ISO-8859-1"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee
                      http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
  version="3.1">

    <servlet>
        <servlet-name>default</servlet-name>
        <servlet-class>org.apache.catalina.servlets.DefaultServlet</servlet-class>
        <init-param>
            <param-name>debug</param-name>
            <param-value>0</param-value>
        </init-param>
        <init-param>
            <param-name>listings</param-name>
            <param-value>false</param-value>
        </init-param>
        <load-on-startup>1</load-on-startup>
        <async-supported>true</async-supported>
    </servlet>

    <servlet>
        <servlet-name>jsp</servlet-name>
        <servlet-class>org.apache.jasper.servlet.JspServlet</servlet-class>
        <init-param>
            <param-name>fork</param-name>
            <param-value>false</param-value>
        </init-param>
        <init-param>
            <param-name>xpoweredBy</param-name>
            <param-value>false</param-value>
        </init-param>
        <load-on-startup>3</load-on-startup>
        <async-supported>true</async-supported>
    </servlet>  


    <!-- The mapping for the default servlet -->
    <servlet-mapping>
        <servlet-name>default</servlet-name>
        <url-pattern>/</url-pattern>
    </servlet-mapping>

    <!-- The mappings for the JSP servlet -->
    <servlet-mapping>
        <servlet-name>jsp</servlet-name>
        <url-pattern>*.jsp</url-pattern>
        <url-pattern>*.jspx</url-pattern>
    </servlet-mapping>    
</web-app>

- Spring web-app web.xml -

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee
                      http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
  version="3.1">    

    <!-- Creates the Spring Container shared by all Servlets and Filters -->
    <listener>
        <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
    </listener>

    <context-param>
        <param-name>webAppRootKey</param-name>
        <param-value>my-async-app</param-value>
    </context-param>

    <context-param>
        <param-name>contextConfigLocation</param-name>
        <param-value>classpath:spring/app-config.xml</param-value>
    </context-param>

    <!-- Handles all requests into the application -->
    <servlet>
        <servlet-name>app</servlet-name>
        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
        <init-param>
            <param-name>contextConfigLocation</param-name>
            <param-value>classpath:spring/controllers-config.xml</param-value> 
        </init-param>
        <load-on-startup>1</load-on-startup>
        <async-supported>true</async-supported>
    </servlet>

    <!-- Maps all /app requests to the DispatcherServlet for handling -->
    <servlet-mapping>
        <servlet-name>app</servlet-name>
        <url-pattern>/app/*</url-pattern>
    </servlet-mapping>
</web-app>

Answer 1

此问题与Tomcat描述的here，here和here中的错误有关。

可能的解决方案：

使用更稳定的Tomcat版本，例如已修复此错误的Tomcat 7.0.47。
使用更高级的调度程序，例如org.springframework.web.servlet.DispatcherServlet

按建议here覆盖HttpServlet：

public class AsyncServlet extends HttpServlet {

    protected void doGet(final HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        if (request.isAsyncStarted()) {
            response.getWriter().write("asyncResult=" + request.getAttribute("asyncResult"));
        } else {
            final AsyncContext asyncContext = request.startAsync(request, response);

            asyncContext.addListener(new AsyncListener() {
                public void onTimeout(AsyncEvent event) throws IOException {
                    request.setAttribute("asyncResult", "timeout\n");
                    asyncContext.dispatch();
                }

                public void onStartAsync(AsyncEvent event) throws IOException {
                }

                public void onError(AsyncEvent event) throws IOException {
                }

                public void onComplete(AsyncEvent event) throws IOException {
                }
            });

            asyncContext.setTimeout(5000L);
        }
    }
}

Answer 2

我通过在application.properties中设置以下内容来解决（解决）此问题：

import 'dart:convert'; import 'package:http/http.dart' as http; import 'package:http/http.dart'; class MyClient extends http.BaseClient { final Map<String, String> defaultHeaders; http.Client _httpClient = new http.Client(); MyClient({this.defaultHeaders = const {}}); @override Future<http.StreamedResponse> send(http.BaseRequest request) { request.headers.addAll(defaultHeaders); return _httpClient.send(request); } @override Future<Response> get(url, {Map<String, String> headers}) { headers.addAll(defaultHeaders); return _httpClient.get(url, headers: headers); } @override Future<Response> post(url, {Map<String, String> headers, body, Encoding encoding}) { headers.addAll(defaultHeaders); return _httpClient.post(url, headers: headers, encoding: encoding); } @override Future<Response> patch(url, {Map<String, String> headers, body, Encoding encoding}) { headers.addAll(defaultHeaders); return _httpClient.patch(url, headers: headers, encoding: encoding); } @override Future<Response> put(url, {Map<String, String> headers, body, Encoding encoding}) { headers.addAll(defaultHeaders); return _httpClient.put(url, headers: headers, body: body, encoding: encoding); } @override Future<Response> head(url, {Map<String, String> headers}) { headers.addAll(defaultHeaders); return _httpClient.head(url, headers: headers); } @override Future<Response> delete(url, {Map<String, String> headers}) { headers.addAll(defaultHeaders); return _httpClient.delete(url, headers: headers); } }

此选项设置异步请求处理超时之前的时间（以毫秒为单位）。将其设置为-1将使它不受限制。

如果您要处理许多请求，请务必小心，因为这很容易耗尽请求处理线程。

Spring Async DeferredResult在Tomcat 8中不起作用

2 个答案: