本文以实例形式剖析了Ajax与servlet的交互，并且代码中有较为详细的注释，以帮助大家阅读理解。具体的实现方法如下：
1.JavaScript部分
var req;
/*通过异步传输XMLHTTP发送参数到ajaxServlet，返回符合条件的XML文档*/
var url;
function getResult()
{
var f=document.getElementById("form_pub");
var key=f.s.options[f.s.selectedIndex].text; //获取对select中文本的引用
if (window.XMLHttpRequest)
{
req = new XMLHttpRequest();
url = "ajaxServlet?action="+key+"&bm=UTF-8";
}else if (window.ActiveXObject)
{
req = new ActiveXObject("Microsoft.XMLHTTP");
url = "ajaxServlet?action="+key+"&bm=gbk";
}
if(req)
{
req.open("GET",url, true);
req.setRequestHeader("Content-Type", "text/html;charset=UTF-8");
//这里如果不设定头部则会导致 firfox 发送数据错误，servlet接受到的参数为乱码，在IE中正常
req.onreadystatechange = complete;
req.send(null);
//req.setRequestHeader("Content-Type", "text/xml; charset=UTF-8");
}
}
/*分析返回的XML文档*/
function complete(){
if (req.readyState == 4)
{
if (req.status == 200)
{
var items=document.getElementById("belong");
//以下为解析返回的XML文档
var xmlDoc = req.responseXML;
var Node=xmlDoc.getElementsByTagName("type_name");
//var str=new Array();
var str=null;
//清空工作
items.innerHTML=""; //删除一个 select内的全部内容
for(var i=0;i<Node.length;i++)
{
str=Node[i];
//alert(str.childNodes[0].nodeValue);
var objectOption=document.createElement("option");
items.options.add(objectOption);
//firfox不支持innerText必须用textContent代替
if (window.ActiveXObject)
{objectOption.innerText=str.childNodes[0].nodeValue;}
else
{objectOption.textContent=str.childNodes[0].nodeValue;}
}
}
}
}
2.servlet端：
package ajax;
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;
import Data_GetConn.GetConn;//这个包是自己写的为获取对mysql的引用
import java.sql.*;//这个包必须有！！
public class ajaxServlet extends HttpServlet{
//private static final String CONTENT_TYPE = "text/xml; charset=UTF-8";//这里最好统一用UTF-8进行编码
public void init() throws ServletException{}
public void doGet(HttpServletRequest request,HttpServletResponse response) throws ServletException, IOException
{
response.setContentType("text/xml; charset=UTF-8");
//以下两句为取消在本地的缓存
response.setHeader("Cache-Control", "no-cache");
response.setHeader("Pragma", "no-cache");
PrintWriter out = response.getWriter();
String action = request.getParameter("action");
String bm = request.getParameter("bm");
if(("gbk").equals(bm))
{
action=new String(action.getBytes("ISO-8859-1"),"gbk");//将获得的数据用gbk从新编码！（感谢董卫老师）
}
else
{
action=new String(action.getBytes("ISO-8859-1"),"gbk");
}
try
{
GetConn wq=new GetConn();
Connection con=wq.getCon();
Statement stmt=con.createStatement();
ResultSet rs=stmt.executeQuery("select items from class where main='"+action+"'");
StringBuffer sb = new StringBuffer();
sb.append("<type>");
while(rs.next())
{
sb.append("<type_name>"+rs.getString(1)+"</type_name>");
}
//sb.append("<type_name>"+action+"</type_name>");
sb.append("</type>");
out.write(sb.toString());//注意这里向jsp输出的流，在script中的截获方法
out.close();
stmt.close();
con.close();
}
catch(Exception ex)
{
}
}
}