AJAX学习笔记7 AJAX实现省市联动

需求:网页上选择对应省份之后,动态的关联出该省份对应的市.选择对应的市之后,动态的关联出该市对应的区

关于省市区全国三级Mysql数据：全国省市区三级地区MySQL数据_biubiubiu0706的博客-CSDN博客

页面加载完毕显示所有省份

package com.web;

import com.alibaba.fastjson.JSON;
import com.pojo.Area;

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.io.PrintWriter;
import java.sql.*;
import java.util.ArrayList;
import java.util.List;

/**
 * @author hrui
 * @date 2023/9/5 16:08
 */
@WebServlet("/liandong")
public class AjaxRequestLiandong extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String f=req.getParameter("f");
        String code = req.getParameter("code");
        Connection conn=null;
        PreparedStatement ps=null;
        ResultSet rs=null;
        List list=new ArrayList<>();
        String sql="";
        try {
            Class.forName("com.mysql.cj.jdbc.Driver");
            conn=DriverManager.getConnection("xxx","xxx","xxx");
            if("0".equals(f)){
                sql="select id,province_id,province_name from table_china_province";
                ps= conn.prepareStatement(sql);
                rs= ps.executeQuery();
                while(rs.next()){
                    String id=rs.getString("id");
                    String c=rs.getString("province_id");
                    String name=rs.getString("province_name");
                    Area l=new Area(name,c);
                    list.add(l);
                }
            }else if("1".equals(f)){
                sql="select id,city_id,city_name from table_china_city where province_id=?";
                ps= conn.prepareStatement(sql);
                ps.setString(1, code);
                rs= ps.executeQuery();
                while(rs.next()){
                    String id=rs.getString("id");
                    String c=rs.getString("city_id");
                    String name=rs.getString("city_name");
                    Area l=new Area(name,c);
                    list.add(l);
                }
            }else if("2".equals(f)){
                sql="select id,area_id,area_name from table_china_area where city_id=?";
                ps= conn.prepareStatement(sql);
                ps.setString(1, code);
                rs= ps.executeQuery();
                while(rs.next()){
                    String id=rs.getString("id");
                    String c=rs.getString("area_id");
                    String name=rs.getString("area_name");
                    Area l=new Area(name,c);
                    list.add(l);
                }
            }


        } catch (ClassNotFoundException | SQLException e) {
            e.printStackTrace();
        }finally {
            if(rs!=null){
                try {
                    rs.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }
            if(ps!=null){
                try {
                    ps.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }
            if(conn!=null){
                try {
                    conn.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }
        }
        resp.setContentType("text/json;charset=utf-8");
        PrintWriter writer = resp.getWriter();
        String s = JSON.toJSONString(list);
        writer.print(s);
    }
}