基于AJAX的长轮询（long-polling）方式实现简单的聊天室程序

2021-10-11 10:56:26

原理：

可以看:http://yiminghe.javaeye.com/blog/294781

AJAX 的出现使得 JavaScript 可以调用 XMLHttpRequest 对象发出 HTTP 请求，JavaScript 响应处理函数根据服务器返回的信息对 HTML 页面的显示进行更新。使用 AJAX 实现“服务器推”与传统的 AJAX 应用不同之处在于：

服务器端会阻塞请求直到有数据传递或超时才返回。
客户端 JavaScript 响应处理函数会在处理完服务器返回的信息后，再次发出请求，重新建立连接。
当客户端处理接收的数据、重新建立连接时，服务器端可能有新的数据到达；这些信息会被服务器端保存直到客户端重新建立连接，客户端会一次把当前服务器端所有的信息取回。

聊天页面的代码：

定义mm.js，定义发送消息，定义接收消息的JS函数

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Ext.onReady(function () {
getMsg();
});
function getMsg() {
Ext.Ajax.request({url:"getMsg", callback:function (options, success, response) {
if (success) {
Ext.DomHelper.append(Ext.get("main"), response.responseText, true);
}
getMsg();
}});
}
function putMsg() {
Ext.Ajax.request({url:"putMsg", params:{message:document.getElementByIdx_x_x("message").value}});
}

下面是获得message的servlet

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package hyjc.listener;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class GetMsg extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html");
PrintWriter out = response.getWriter();
MessageList m = MessageList.getInstance();
boolean end = false;
while (!end) {
System.out.println("before get");
String msg = m.get();
System.out.println("after get " + msg);
out.write(msg + "
");
if (m.isEmpty()) {
end = true;
}
}
out.close();
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
}

下面是添加消息的servlet

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package hyjc.listener;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class PutMsg extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html");
System.out.println("put message");
PrintWriter out = response.getWriter();
out.flush();
String msg = request.getParameter("message");
if (null != msg) {
MessageList.getInstance().add(msg);
} else {
System.out.println("添加消息:" + msg + "成果");
}
out.close();
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
}

下面是存放消息的消息队列，内部用阻塞队列使用

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下面是演示效果，输入message，点击submit，就会添加到MessageList中，然后会在GetMsg中继续执行，实现长连接