Servlet 3.0与纯JavaScript通过Ajax交互的实例详解

<?xml version="1.0" encoding="UTF-8"?> 
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
  xmlns="http://java.sun.com/xml/ns/javaee" 
  xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" 
  version="3.0"> 
</web-app> 

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> 
<html xmlns="http://www.w3.org/1999/xhtml"> 
<head> 
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> 
<title>Js</title> 
</head> 
 
<body> 
  <input type="text" id="param1" /> 
  <input type="text" id="param2" /> 
  <button onclick="ajax()">Go!</button> 
</body> 
</html> 
<script> 
  //创建Ajax对象，不同浏览器有不同的创建方法，其实本函数就是一个简单的new语句而已。  
  function createXMLHttpRequest() { 
    var XMLHttpRequest1; 
    if (window.XMLHttpRequest) { 
      XMLHttpRequest1 = new XMLHttpRequest(); 
    } else if (window.ActiveXObject) { 
      try { 
        XMLHttpRequest1 = new ActiveXObject("Msxml2.XMLHTTP"); 
      } catch (e) { 
        XMLHttpRequest1 = new ActiveXObject("Microsoft.XMLHTTP"); 
      } 
    } 
    return XMLHttpRequest1; 
  } 
  function ajax() { 
    //param1与param2就是用户在输入框的两个参数 
    var param1=document.getElementById("param1").value; 
    var param2=document.getElementById("param2").value; 
    var XMLHttpRequest1 = createXMLHttpRequest(); 
    //指明相应页面  
    var url = "./ajaxRequest"; 
    XMLHttpRequest1.open("POST", url, true); 
    //这里没法解释，你所有JavaScript的请求头都这样写就对了，不会乱码  
    XMLHttpRequest1.setRequestHeader("Content-Type", 
        "application/x-www-form-urlencoded"); 
    //对于ajaxRequest，本js.html将会传递param1与param2给你。  
    XMLHttpRequest1.send("param1=" + param1 + "¶m2=" + param2); 
    //对于返回结果怎么处理的问题  
    XMLHttpRequest1.onreadystatechange = function() { 
      //这个4代表已经发送完毕之后  
      if (XMLHttpRequest1.readyState == 4) { 
        //200代表正确收到了返回结果  
        if (XMLHttpRequest1.status == 200) { 
          //弹出返回结果  
          alert(XMLHttpRequest1.responseText); 
        } else { 
          //如果不能正常接受结果，你肯定是断网，或者我的服务器关掉了。  
          alert("网络连接中断！"); 
        } 
      } 
    }; 
  } 
</script> 

package jsServletAjax; 
import java.io.*;  
import javax.servlet.*;  
import javax.servlet.http.*;  
import javax.servlet.annotation.*;  
  
//说明这个Servlet是没有序列号的  
@SuppressWarnings("serial")  
//说明这个Servlet的名称是ajaxRequest，其地址是/ajaxRequest 
//这与在web.xml中设置是一样的  
@WebServlet(name = "ajaxRequest", urlPatterns = { "/ajaxRequest" })  
public class Servlet extends HttpServlet {  
  //放置用户之间通过直接在浏览器输入地址访问这个servlet  
  protected void doGet(HttpServletRequest request,  
      HttpServletResponse response) throws ServletException, IOException {  
    PrintStream out = new PrintStream(response.getOutputStream());  
    response.setContentType("text/html;charSet=utf-8");  
    out.print("请正常打开此页"); 
  }  
  
  protected void doPost(HttpServletRequest request,  
      HttpServletResponse response) throws ServletException, IOException { 
    response.setContentType("text/html; charset=utf-8"); 
    PrintWriter pw = response.getWriter(); 
    request.setCharacterEncoding("utf-8"); 
    String param1=request.getParameter("param1"); 
    String param2=request.getParameter("param2");     
    pw.print("前台传来了参数：param1="+param1+"，param2="+param2); 
    pw.flush(); 
    pw.close(); 
  }  
}