Servlet 3异步+Html5 SSE示例

1.容器Tomcat 8.0
conf/web.xml 配置mime-type

  <mime-mapping>
    <extension>sse</extension>
    <mime-type>text/event-stream</mime-type>
  </mime-mapping>

2.异步的Servlet

import java.io.IOException;
import java.io.PrintWriter;
import java.util.Date;
import javax.servlet.AsyncContext;
import javax.servlet.AsyncEvent;
import javax.servlet.AsyncListener;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@WebServlet(urlPatterns = { "/echo" }, asyncSupported = true) 
public class EchoPushServlet extends HttpServlet {

    private static final long serialVersionUID = 1L;
    private final static int DEFAULT_TIME_OUT = 10 * 60 * 1000;  

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // TODO Auto-generated method stub
        resp.setContentType("text/event-stream");
        resp.setCharacterEncoding("UTF-8");

        AsyncContext actx = req.startAsync(req, resp);
        actx.setTimeout(DEFAULT_TIME_OUT);  
        actx.addListener(new AsyncListener() {
            @Override
            public void onComplete(AsyncEvent arg0) throws IOException {
                // TODO Auto-generated method stub
                System.out.println("[echo]event complete:"+arg0.getSuppliedRequest().getRemoteAddr());
            }
            @Override
            public void onError(AsyncEvent arg0) throws IOException {
                // TODO Auto-generated method stub
                System.out.println("[echo]event has error");
            }
            @Override
            public void onStartAsync(AsyncEvent arg0) throws IOException {
                // TODO Auto-generated method stub
                System.out.println("[echo]event start:"+arg0.getSuppliedRequest().getRemoteAddr());
            }
            @Override
            public void onTimeout(AsyncEvent arg0) throws IOException {
                // TODO Auto-generated method stub
                System.out.println("[echo]event time lost");
            } 
        });
        new Thread(new AsyncWebService(actx)).start();
    }
}
class AsyncWebService implements Runnable {
    AsyncContext ctx;
    public AsyncWebService(AsyncContext ctx) {
        this.ctx = ctx;
    }
    public void run() {
        try {
            //等待十秒钟，以模拟业务方法的执行
            Thread.sleep(10000);
            PrintWriter out = ctx.getResponse().getWriter();
            out.println( "data:"+new Date() + "\r\n");
            out.flush();
            ctx.complete();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

注意:
1.servlet 3增加了注解,asyncSupported表示异步

@WebServlet(urlPatterns = { "/echo" }, asyncSupported = true) 

2.由于请求流有异步，所以相关的filter,servlet都要开启异步

<async-supported>true</async-supported>

如下web.xml

 <servlet>
    <servlet-name>apobates_client</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>apobates_client</servlet-name>
    <url-pattern>/</url-pattern>
  </servlet-mapping>
  <filter>
    <filter-name>CharacterEncodingFilter</filter-name>
    <filter-class>org.springframework.web.filter.CharacterEncodingFilter</filter-class>
    <async-supported>true</async-supported>
    <init-param>
      <param-name>encoding</param-name>
      <param-value>UTF-8</param-value>
    </init-param>
    <init-param>
      <param-name>forceEncoding</param-name>
      <param-value>true</param-value>
    </init-param>
  </filter>
  <filter-mapping>
    <filter-name>CharacterEncodingFilter</filter-name>
    <url-pattern>/*</url-pattern>
  </filter-mapping>

少了这步会出现以下异常

15-Jan-2017 09:54:09.610 SEVERE [http-nio-80-exec-10] org.apache.catalina.core.StandardWrapperValve.invoke Servlet.service() for servlet [com.apobates.servlet.EchoPushServlet] in context with path [] threw exception
 java.lang.IllegalStateException: A filter or servlet of the current chain does not support asynchronous operations.
    at org.apache.catalina.connector.Request.startAsync(Request.java:1621)
    at org.apache.catalina.connector.RequestFacade.startAsync(RequestFacade.java:1037)
    at com.apobates.servlet.EchoPushServlet.doGet(EchoPushServlet.java:31)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:622)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:292)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:240)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
    at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:88)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:106)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:240)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:212)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:141)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
    at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:616)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:528)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1099)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:670)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1520)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1476)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Thread.java:745)

3.输出的消息要符合SSE的格式,以data:开头

out.println( "data:"+new Date() + "\r\n");

3.前端获取消息

    <script type="text/javascript">
    var source=new EventSource("${initParam.domain}/echo");
    source.onmessage=function(event) {
        //console.log(event.data + "<br />");
        document.getElementById('eventDetails').innerHTML=event.data;
    };
    </script>

最后:
1.相关学习资源
Server-Sent Events
HTML5 Server-Sent Events with Java Servlets example
Servlet 3.0 新特性详解
Spring+Websocket实现消息的推送
Servlet 3.0 实战：异步 Servlet 与 Comet 风格应用程序

2.有图有真像
1.tomcat/log/catalina.out输出

2.浏览器的开发者工具网络中的请求

3.某个请求的头信息

4.某个请求的响应内容