Ajax入门

AJAX：即“Asynchronous Javascript And XML”（异步的JavaScript和XML），是指一种创建交互式网页应用的网页开发技术，尤其是在一种在无需重新加载整个网页的情况下，能够更新部分网页的技术。
传统Web开发
World Wide Web（简称Web）：是随着Internet的普及使用而发展起来的一门技术，其开发模式是一种请求→刷新→响应的模式，每个请求由单独的一个页面来显示，发送一个请求就会重新获取这个页面。
!

验证用户名是否注册

index.jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" %>

  
        
        
      
  
  
    
Reg Page
    

        


        
        注册
    

CheckUsernameServlet.java

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

@WebServlet(name = "CheckUsernameServlet",urlPatterns = "/checkUsername")
public class CheckUsernameServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // 获取请求参数
        String name = request.getParameter("name");
        // 调dao查询该用户名是否存在
        if("mike".equals(name)){
            // 失败
            response.getWriter().println(0);
        }else{
            response.getWriter().println(1);
        }
    }
}

根据id查询用户和查询全部用户,响应ajax只能响应字符串给res

把对象序列化成字符串，需要使用jackson或fastjson，可以自己到maven库下载
serch.jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" %>


    
    
    


    
Serch Page
    

        
        查询
        查询全部
    
    

SerchByIdServlet.java

import com.alibaba.fastjson.JSON;
import com.neuedu.pojo.Userinfo;

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

@WebServlet(name = "SerchByIdServlet",urlPatterns = "/serchById")
public class SerchByIdServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // 获取请求参数
        String userid = request.getParameter("userid");
        // 调dao层查询该id员工所有信息
        Userinfo userinfo = new Userinfo();
        userinfo.setId(Integer.parseInt(userid));
        userinfo.setAge(30);
        userinfo.setName("leo");
        userinfo.setSex("男");
        // 响应ajax请求
        //  JSON.toJSONString会把对象序列化成json字符串
        String str = JSON.toJSONString(userinfo);
        System.out.println(str);
        response.getWriter().println(str);
    }
}

SerchAllServlet.java

import com.alibaba.fastjson.JSON;
import com.neuedu.pojo.Userinfo;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

@WebServlet(name = "SerchAllServlet",urlPatterns = "/serchAll")
public class SerchAllServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        Userinfo userinfo1 = new Userinfo();
        userinfo1.setId(1001);
        userinfo1.setName("tom");
        userinfo1.setSex("man");
        userinfo1.setAge(30);
        Userinfo userinfo2 = new Userinfo();
        userinfo2.setId(1002);
        userinfo2.setName("lucy");
        userinfo2.setSex("girl");
        userinfo2.setAge(33);
        Userinfo userinfo3 = new Userinfo();
        userinfo3.setId(1003);
        userinfo3.setName("lilei");
        userinfo3.setSex("man");
        userinfo3.setAge(20);

        List list = new ArrayList<>();
        list.add(userinfo1);
        list.add(userinfo2);
        list.add(userinfo3);
        String str = JSON.toJSONString(list);
        System.out.println(str);
        response.getWriter().println(str);
    }
}

ajax简化写法