dwr push技术，基于长连接

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mb5fb94c9d4a0ba 2023-05-17 14:08:17

文章标签 dwr javascript html servlet encoding 文章分类 音视频

DWR的push技术是让服务器每次发送广播时，把这个广播推送给每个客户端，不用客户端去刷新，据说DWR的推送是基于长连接的，性能不错。可以在后台通过 ScriptSession 来执行一些 javascript 的 function 或者是 style 等操作，可以在服务器上将一些数据推送到客户端机器上。

修改web.xml，在dwr的servlet中启用dwr的Reverse Ajax，即加入：

<init-param>
             <param-name>activeReverseAjaxEnabled</param-name>
             <param-value>true</param-value>
</init-param>Web.xml配置
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://java.sun.com/xml/ns/j2ee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    version="2.4"
    xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee  >
     <servlet>
           <servlet-name>dwr</servlet-name>
           <servlet-class>org.directwebremoting.servlet.DwrServlet</servlet-class>
           <init-param>
                 <param-name>debug</param-name>
                 <param-value>true</param-value>
           </init-param>
           <init-param>
                 <param-name>activeReverseAjaxEnabled</param-name>
                 <param-value>true</param-value>
           </init-param>
           <init-param>
                 <param-name>crossDomainSessionSecurity</param-name>
                 <param-value>false</param-value>
           </init-param>
     </servlet>
     <servlet>
           <servlet-name>Sender</servlet-name>
           <servlet-class>com.dwr.servlet.Sender</servlet-class>
     </servlet>
     <servlet-mapping>
           <servlet-name>dwr</servlet-name>
           <url-pattern>/dwr/*</url-pattern>
     </servlet-mapping>
     <servlet-mapping>
           <servlet-name>Sender</servlet-name>
           <url-pattern>/notify.do</url-pattern>
     </servlet-mapping>
     <welcome-file-list>
           <welcome-file>index.jsp</welcome-file>
     </welcome-file-list>
</web-app>
创建一个请求页面：
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
     <head>
           <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
           <title>index页面</title>
     </head>
     <body>
           <form action="notify.do">
                 <input type="text" name="message" />
                 <input type="submit" value="提交">
           </form>
     </body>
</html>
创建一个发送广播的Servlet
packagecom.dwr.servlet;
importjava.io.IOException;
importjava.util.Collection;
importjavax.servlet.ServletException;
importjavax.servlet.http.HttpServlet;
importjavax.servlet.http.HttpServletRequest;
importjavax.servlet.http.HttpServletResponse;
importorg.directwebremoting.ScriptBuffer;
importorg.directwebremoting.ScriptSession;
importorg.directwebremoting.ServerContext;
importorg.directwebremoting.ServerContextFactory;
public class Sender extends HttpServlet {
     private static final long serialVersionUID = 221673813297384002L;
     protected voiddoGet(HttpServletRequest request,
                 throws ServletException, IOException {
          
                       .get(getServletContext());
          
                       .getAllScriptSessions();
           // Collection<ScriptSession> sessions =
           // wctx.getScriptSessionsByPage("/poject/test.html");
          "message");
           if (message == null) {
                 "empty";
          
           new ScriptBuffer();
          "showMessage(").appendData(message)
                      ");");
           for (ScriptSession scriptSession : scriptSessions) {
                
          
    
}
添加一个html页面，用来接收服务端广播：
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
     <head>
           <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
           <title>Client1的页面</title>
           <script type='text/javascript' src='dwr/engine.js'></script>
           <script type="text/javascript">
                true);
                 functionshowMessage(msg) {
                      
                
           </script>
     </head>
     <body>
     </body>
</html>
打开添加的html页面，然后让Sender发送一个广播， html页面就会自动弹出一个javascript对话框，到此，dwr的推送就完成了。