jQuery+Ajax实现用户名重名实时检测

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

import com.dao.LoginDao;
import com.user.UserInfo;

public class UserServlet extends HttpServlet {

public void doPost(HttpServletRequest request,HttpServletResponse response)
throws ServletException,IOException {

response.setContentType("text/html; charset=UTF-8"); // 设置响应结果的格式为text/html，字符集为UTF-8
response.setCharacterEncoding("UTF-8"); // 设置响应结果的字符编码为UTF-8
// 禁止缓存
response.setHeader("Cache-Control","no-store,no-cache,must-revalidate");
response.setHeader("Cache-Control","post-check=0,pre-check=0");
response.setDateHeader("Expires",0);
response.setHeader("Pragma","no-cache");

PrintWriter out = response.getWriter();
out.println("<?xml version="1.0" encoding="utf-8"?>");
// 从httpRequest()方法中获得请求参数值
// 通过httpRequest()方法封装的请求参数被编码为UTF-8格式，此处若想还原原来的编码格式，则需要通过UTF-8格式解码

String userName = request.getParameter("userName");
String result = null;
boolean check = LoginDao.getInstance().checkUserName(userName.trim()); // 查找数据库是否存在该用户名
if (check) {
result = "该用户已经被使用";
} else {
result = "该用户名可以使用";
}
response.getWriter().print(result); // 将结果输出到response响应流中
}

@Override
protected void doGet(HttpServletRequest req,HttpServletResponse resp)
throws ServletException,IOException {
this.doPost(req,resp);
}

}