用自写的jQuery库+Ajax实现了省市联动

1. 省市联动：在网页上，选择对应的省份之后，动态的关联出该省份对应的市。选择对应的市之后，动态地关联出城市对应的区。

2. 设计数据库表

t_area （区域表）
id(PK-自增)	  code		name		pcode
---------------------------------------------
1				001		 河北省		null
2				002		 河南省		null
3				003		 石家庄	    001
4				004		 邯郸	    001
5				005		 郑州	    002
6				006		 洛阳	    002
7               007      江苏       null
8               008      南京       007将全国所有的省、市、区、县等信息都存储到一张表当中。
采用的存储方式实际上是code pcode形势。

3. 这里只是一个模拟，所以建的数据库是不完整的，想要完整的数据库，可以去网上找。

4. 上代码

（1）自写的jQquery库

function jQuery(selector){ // selector可能是#id，也可以是其他的选择器，例如类选择器：.classif(typeof selector == "string"){if (selector.charAt(0) == '#') {domObj = document.getElementById(selector.substring(1));return new jQuery();}}if(typeof selector == "function"){window.onload = selector;}this.html = function(htmlStr){domObj.innerHTML = htmlStr;}this.click = function(fun){domObj.onclick = fun;}this.val = function(v){if (v == undefined) {return domObj.value;}else{domObj.value = v;}}this.change = function(fun){domObj.onchange = fun;}// 静态的方法：发送ajax请求jQuery.ajax = function(jsonArgs){var xhr = new XMLHttpRequest();xhr.onreadystatechange = function(){if (this.readyState == 4) {if (this.status == 200) {var jsonObj = JSON.parse(this.responseText);jsonArgs.success(jsonObj);}}}if (jsonArgs.type.toUpperCase() == "POST") {xhr.open("POST",jsonArgs.url,jsonArgs.async);xhr.setRequestHeader("Content-Type","application/x-www-form-urlencoded")xhr.send(jsonArgs.data);}if (jsonArgs.type.toUpperCase() == "GET") {xhr.open("GET",jsonArgs.url + "?" + jsonArgs.data,jsonArgs.async);xhr.send();}}
}
$=jQuery;

（2）html文件（Ajax请求）

<!DOCTYPE html>
<html lang="en">
<head><meta charset="UTF-8"><title>用ajax实现省市联动</title>
</head>
<body>
<!--引入自己编写的jQuery库-->
<script type="text/javascript" src="/ajax/js/jQuery-1.0.0.js"></script>
<!--<script src="https://code.jquery.com/jquery-3.6.0.min.js"></script>-->
<script type="text/javascript">
$(function(){// 发送ajax请求，获取所有的省份，省份的pcode是null$.ajax({type: "get",url : "/ajax/listArea",data : "t=" + new Date().getTime(),async : true,success:function(jsonArr){var html = "<option value=\"\">--请选择省份--</option>";for (var i = 0; i < jsonArr.length; i++) {var area = jsonArr[i];html += "<option value=\""+area.code+"\">"+area.name+"</option>"}$("#province").html(html)}})// 只要change发生，就发送ajax请求$("#province").change(function(){$.ajax({type: "get",url : "/ajax/listArea",data : "t=" + new Date().getTime()+ "&pcode="+this.value,async : true,success:function(jsonArr){var html = "<option value=\"\">--请选择市--</option>";for (var i = 0; i < jsonArr.length; i++) {var area = jsonArr[i];html += "<option value=\""+area.code+"\">"+area.name+"</option>"}$("#city").html(html)}})})
})
</script>
<select id="province"></select>
<select id="city"></select>
</body>
</html>

（3）servlet文件（后端）

package com.bjpowernode.ajax.servlet;import com.alibaba.fastjson.JSON;
import com.bjpowernode.ajax.bean.Area;
import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;import java.io.IOException;
import java.sql.*;
import java.util.ArrayList;/*** 动态获取所有的省份*/
@WebServlet("/listArea")
public class ListAreaServlet extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {// 连接数据库，获取所有的对应区域，最终响应一个JSON格式的字符串给WEB前端Connection conn = null;PreparedStatement ps = null;ResultSet rs= null;ArrayList<Area> areas = new ArrayList<>();String pcode = request.getParameter("pcode");String sql;try {Class.forName("com.mysql.cj.jdbc.Driver");String url = "jdbc:mysql://localhost:3306/bjpowernode?useUnicode=true&characterEncoding=UTF-8";String user = "root";String password = "1234";conn = DriverManager.getConnection(url,user,password);if (pcode == null){sql = "select code,name from t_area where pcode is null";ps = conn.prepareStatement(sql);}else{sql = "select code,name from t_area where pcode = ?";ps = conn.prepareStatement(sql);ps.setString(1,pcode);}rs = ps.executeQuery();while (rs.next()) {String code = rs.getString("code");String name = rs.getString("name");Area area = new Area(code, name);areas.add(area);}} catch (ClassNotFoundException e) {throw new RuntimeException(e);} catch (SQLException e) {throw new RuntimeException(e);} finally{if (rs != null) {try {rs.close();} catch (SQLException e) {throw new RuntimeException(e);}}if (ps != null) {try {ps.close();} catch (SQLException e) {throw new RuntimeException(e);}}if (conn != null) {try {conn.close();} catch (SQLException e) {throw new RuntimeException(e);}}}response.setContentType("text/html,charset=UTF-8");String json = JSON.toJSONString(areas);response.getWriter().print(json);}}

5. 展示效果