1. 省市聯動：在網頁上，選擇對應的省份之后，動態的關聯出該省份對應的市。選擇對應的市之后，動態地關聯出城市對應的區。
2. 設計數據庫表
t_area （區域表）
id(PK-自增) code name pcode
---------------------------------------------
1 001 河北省 null
2 002 河南省 null
3 003 石家莊 001
4 004 邯鄲 001
5 005 鄭州 002
6 006 洛陽 002
7 007 江蘇 null
8 008 南京 007將全國所有的省、市、區、縣等信息都存儲到一張表當中。
采用的存儲方式實際上是code pcode形勢。3. 這里只是一個模擬，所以建的數據庫是不完整的，想要完整的數據庫，可以去網上找。
4. 上代碼
（1）自寫的jQquery庫
function jQuery(selector){ // selector可能是#id，也可以是其他的選擇器，例如類選擇器：.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;}// 靜態的方法：發送ajax請求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請求）
<!DOCTYPE html>
<html lang="en">
<head><meta charset="UTF-8"><title>用ajax實現省市聯動</title>
</head>
<body>
<!--引入自己編寫的jQuery庫-->
<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">
$(function(){// 發送ajax請求，獲取所有的省份，省份的pcode是null$.ajax({type: "get",url : "/ajax/listArea",data : "t=" + new Date().getTime(),async : true,success:function(jsonArr){var html = "<option value=\"\">--請選擇省份--</option>";for (var i = 0; i < jsonArr.length; i++) {var area = jsonArr[i];html += "<option value=\""+area.code+"\">"+area.name+"</option>"}$("#province").html(html)}})// 只要change發生，就發送ajax請求$("#province").change(function(){$.ajax({type: "get",url : "/ajax/listArea",data : "t=" + new Date().getTime()+ "&pcode="+this.value,async : true,success:function(jsonArr){var html = "<option value=\"\">--請選擇市--</option>";for (var i = 0; i < jsonArr.length; i++) {var area = jsonArr[i];html += "<option value=\""+area.code+"\">"+area.name+"</option>"}$("#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;/*** 動態獲取所有的省份*/
@WebServlet("/listArea")
public class ListAreaServlet extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {// 連接數據庫，獲取所有的對應區域，最終響應一個JSON格式的字符串給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
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