AjaxServlet:

package servlet;

import java.io.IOException;

import java.io.Writer;

import javax.servlet.ServletException;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

/*

 * 处理异步请求

 */

public class AjaxServlet extends HttpServlet{

    @Override

    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        //处理请求乱码

        req.setCharacterEncoding("utf-8");

        //获取注册数据

        String username = req.getParameter("username");

        System.out.println("ajax------"+username);

        //处理响应乱码

        resp.setContentType("text/html;charset=utf-8");

        //响应客户端PrintWriter

        /*

         * json:{}对象  []数组  键:值,

         * 相应到客户端的code=1代表用户名已存在

         * code=0代表用户名不存在

         */

        String rel="{\"code\":\"1\"}";

        Writer w = resp.getWriter();

        if(!"admin".equalsIgnoreCase(username)) {

           rel="{\"code\":\"0\"}";

        }

        w.write(rel);

        w.flush();

        w.close();

    }

}

ajax

原文：https://www.cnblogs.com/Zs-xin/p/11722287.html