之前小狼一直用的最简单的文本内容响应，从今天起，我们将开始处理xml响应，不知道大家还记得dom4j吗。。。。算了，今天就用最简单也是最容易理解的jsp处理xml响应

我们先做铺垫，玩一个servlet作为中央处理器

public void doPost(HttpServletRequest request,HttpServletResponse response)
	throws ServletException,IOException {
		response.setContentType("text/xml;charset=UTF-8");
		PrintWriter out = response.getWriter();
		String uname = request.getParameter("uname");
		
		StringBuilder bd = new StringBuilder();
		bd.append("<userInfo>");
		bd.append("<username>");

		if (uname == null || uname.length() == 0) {
			bd.append("请选择用户账号");
		} else {
			bd.append(uname);
		}
		bd.append("</username>");
		bd.append("</userInfo>");
		out.print(bd.toString());
		out.flush();
		out.close();
	}

  function checkStatus(){
	        if(xmlHttpRequest.readyState==4&&xmlHttpRequest.status==200){
	            var result=xmlHttpRequest.responseXML;
	            if(result){
	                var userNodes=result.getElementsByTagName("username");
	                
	                if(userNodes.length>0){
	                     var username =userNodes[0].firstChild.nodeValue;
	                     document.getElementById("username").value=username;
	                }
	                
	            }
	        
	        }
	     
	     }