Ajax 异步加载解析

xmlhttp.open("POST","ajax_test.asp",true);
xmlhttp.setRequestHeader("Content-type","application/x-www-form-urlencoded");
// 在send方法中指定要传输的参数信息即可
xmlhttp.send("fname=Bill&lname=Gates");

客户端更新页面

对于Ajax来说，顾名思义。是采用xml形式来传输数据的。但是目前而言，这不再是唯一的一种形式了。那么我们怎么将获取到的数据更新到网页上呢？有如下两种方式。
 •如果来自服务器的响应并非 XML，请使用 responseText 属性。
 document.getElementById("myDiv").innerHTML=xmlhttp.responseText;

 •如果来自服务器的响应是 XML，而且需要作为 XML 对象进行解析，请使用 responseXML 属性： 

xmlDoc=xmlhttp.responseXML;
txt="";
x=xmlDoc.getElementsByTagName("ARTIST");
for (i=0;i<x.length;i++)
 {
 txt=txt + x[i].childNodes[0].nodeValue + "<br />";
 }
document.getElementById("myDiv").innerHTML=txt;

实例体验

了解了这些基础语法之后，我们就可以在实际的开发中简单的应用了。为了更好的完成此次实验，我先做了一个简单的JavaWeb，来处理我们的Ajax请求。

使用Servlet方式

AjaxServlet.java

package one;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class AjaxServlet
 */
@WebServlet("/AjaxServlet")
public class AjaxServlet extends HttpServlet {
 private static final long serialVersionUID = 1L;

 /**
  * @see HttpServlet#HttpServlet()
  */
 public AjaxServlet() {
  super();
  // TODO Auto-generated constructor stub
 }

 /**
  * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse
  *  response)
  */
 protected void doGet(HttpServletRequest request, HttpServletResponse response)
   throws ServletException, IOException {
  // TODO Auto-generated method stub
  //response.getWriter().append("Served at: ").append(request.getContextPath());
  String userinput = request.getParameter("userinput");
  System.out.println("客户端连接！");
  System.out.println("请求信息为：" + userinput);
  PrintWriter out = response.getWriter();
  if(userinput.equals("") || userinput.length()<6) {
   response.setContentType("text/html;charset=UTF-8");
   response.setCharacterEncoding("UTF-8");
   response.setHeader("Content-Type", "text/html;charset=utf-8");
   out.write("<h3>the length of input string must be more than 6!</h3>");
  }else{
   response.setContentType("text/html;charset=UTF-8");
   response.setCharacterEncoding("UTF-8");
   response.setHeader("Content-Type", "text/html;charset=utf-8");
   out.println("<h3>Correct!</h3>");
  }
  out.close();
 }

 /**
  * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse
  *  response)
  */
 protected void doPost(HttpServletRequest request, HttpServletResponse response)
   throws ServletException, IOException {
  // TODO Auto-generated method stub
  doGet(request, response);
 }

}

								 
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