【JavaWeb-jQuery】網站 --- 應用 Ajax，jQuery 實作級聯查詢-有解無憂

網站功能：

網頁打開的時候，自動加載省份資訊，用戶通過選擇不同的省份串列值，對應的城市資訊也隨之變化，

網站結構：

網站預覽：

建表陳述句：

CREATE TABLE `pro` (
    `id` int NOT NULL AUTO_INCREMENT,
    `name` varchar(255) DEFAULT NULL,
    `jiancheng` varchar(255) DEFAULT NULL,
    `shenghui` varchar(255) DEFAULT NULL,
    PRIMARY KEY (`id`)
);

INSERT INTO `pro` VALUES ('1','河北','冀','石家莊');
INSERT INTO `pro` VALUES ('2','山西','晉','太原市');
INSERT INTO `pro` VALUES ('3','內蒙古','蒙','呼和浩特市');
INSERT INTO `pro` VALUES ('4','遼寧','遼','沈陽');
INSERT INTO `pro` VALUES ('5','江蘇','蘇','南京');
INSERT INTO `pro` VALUES ('6','浙江','浙','杭州');
INSERT INTO `pro` VALUES ('7','安徽','皖','合肥');
INSERT INTO `pro` VALUES ('8','福建','閩','福州');
INSERT INTO `pro` VALUES ('9','江西','贛','南昌');

DROP TABLE IF EXISTS `city`;
CREATE TABLE `city` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(255) DEFAULT NULL,
  `provinceid` int(11) DEFAULT NULL,
  PRIMARY KEY (`id`)
);


INSERT INTO `city` VALUES ('1', '石家莊市', '1');
INSERT INTO `city` VALUES ('2', '秦皇島', '1');
INSERT INTO `city` VALUES ('3', '保定市', '1');
INSERT INTO `city` VALUES ('4', '張家口', '1');
INSERT INTO `city` VALUES ('5', '南昌市', '9');
INSERT INTO `city` VALUES ('6', '九江市', '9');
INSERT INTO `city` VALUES ('7', '宜春市', '9');
INSERT INTO `city` VALUES ('8', '福州市', '8');
INSERT INTO `city` VALUES ('9', '廈門市', '8');
INSERT INTO `city` VALUES ('10', '泉州市', '8');
INSERT INTO `city` VALUES ('11', '龍巖市', '8');
INSERT INTO `city` VALUES ('12', '太原', '2');
INSERT INTO `city` VALUES ('13', '大同', '2');
INSERT INTO `city` VALUES ('14', '呼和浩特', '3');
INSERT INTO `city` VALUES ('15', '包頭', '3');
INSERT INTO `city` VALUES ('16', '呼倫貝爾', '3');

index.jsp（網站歡迎資源檔案）：

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>省市級聯查詢</title>

    <script type="text/javascript" src="https://www.cnblogs.com/Burning-youth/p/js/jquery-3.6.0.js"></script>
    <script type="text/javascript">
        //自定義函式，用于加載省份資料
        function getData() {
            $.ajax({
                url: "queryProvince",
                dataType: "json",
                success: function (resp) {
                    //洗掉舊的省份select子物件
                    $("#province").empty();
                    //保留“--請選擇--”子物件
                    $("#province").append("<option value=''>" + "--請選擇--" + "</option>");
                    //將省份名稱打到省份select上
                    $.each(resp, function (i, n) {
                        $("#province").append("<option value='" + n.provinceId + "'>" + n.provinceName + "</option>");
                    });
                }
            });
        }
        
        //自定義函式，用于處理服務端回傳的資料
        function callBack(resp) {
            //清空舊的省份串列子物件
            $("#city").empty();
            $.each(resp,function (i, n) {
                $("#city").append("<option value '" + n.cityId + "'>" + n.cityName + "</option>");
            });
        }

        $(function () {
            //加載省份資訊
            getData();

            //省份串列選中值改變時，呼叫的方法：
            $("#province").change(function () {
                //獲取已被選中的串列值
                var id = $("#province>option:selected").val();
                //以 get 方式向服務端發送請求
                $.get("queryCity", {provinceId: id}, callBack, "json");

            });

        })

    </script>
</head>
<body>
<p>省市級聯查詢，使用 Ajax，jQuery</p>
<table border="1px">
    <tr>
        <td>省份：</td>
        <td>
            <select id="province">
                <option value="">--請選擇--</option>
            </select>
        </td>
    </tr>

    <tr>
        <td>城市：</td>
        <td>
            <select id="city">
                <option value="">--請選擇--</option>
            </select>
        </td>
    </tr>
</table>
</body>
</html>

com.burnyouth.util.JdbcUtil（JDBC工具類）：

package com.burnyouth.util;

import java.sql.*;

public class JdbcUtil {
    static {
        try {
            Class.forName("com.mysql.cj.jdbc.Driver");
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
    }

    private JdbcUtil() {
    }

    public static Connection getConnection() throws SQLException {
        return DriverManager.getConnection("jdbc:mysql://localhost:3306/burning_youth"
                , "root", "888");
    }

    public static void close(Connection connection, Statement statement, ResultSet resultSet) {
        if (resultSet != null) {
            try {
                resultSet.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
        if (statement != null) {
            try {
                statement.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
        if (connection != null) {
            try {
                connection.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
}

com.burnyouth.entity.Province（省份物體類）：

package com.burnyouth.entity;

public class Province {
    private Integer provinceId;
    private String provinceName;

    public Province() {
    }

    public Integer getProvinceId() {
        return provinceId;
    }

    public void setProvinceId(Integer provinceId) {
        this.provinceId = provinceId;
    }

    public String getProvinceName() {
        return provinceName;
    }

    public void setProvinceName(String provinceName) {
        this.provinceName = provinceName;
    }
}

com.burnyouth.entity.City（城市物體類）：

package com.burnyouth.entity;

public class Province {
    private Integer provinceId;
    private String provinceName;
    private String jianCheng;
    private String shengHui;

    public Province() {
    }

    public Province(Integer provinceId, String provinceName, String jianCheng, String shengHui) {
        this.provinceId = provinceId;
        this.provinceName = provinceName;
        this.jianCheng = jianCheng;
        this.shengHui = shengHui;
    }

    public Integer getProvinceId() {
        return provinceId;
    }

    public void setProvinceId(Integer provinceId) {
        this.provinceId = provinceId;
    }

    public String getProvinceName() {
        return provinceName;
    }

    public void setProvinceName(String provinceName) {
        this.provinceName = provinceName;
    }

    public String getJianCheng() {
        return jianCheng;
    }

    public void setJianCheng(String jianCheng) {
        this.jianCheng = jianCheng;
    }

    public String getShengHui() {
        return shengHui;
    }

    public void setShengHui(String shengHui) {
        this.shengHui = shengHui;
    }
}

com.burnyouth.dao.QueryProvinceDao（連接資料庫，進行查詢操作并回傳資料）：

package com.burnyouth.dao;

import com.burnyouth.entity.City;
import com.burnyouth.entity.Province;
import com.burnyouth.util.JdbcUtil;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;

public class QueryProvinceDao {
    //查詢資料中所有省份
    public List<Province> queryProvince(){
        Connection connection = null;
        PreparedStatement ps = null;
        ResultSet resultSet = null;
        List<Province> provinces = new ArrayList<>();
        try {
            connection = JdbcUtil.getConnection();
            //按照id升序輸出
            String sql = "select * from pro order by id";
            ps = connection.prepareStatement(sql);
            resultSet = ps.executeQuery();
            while (resultSet.next()) {
                Province province = new Province();
                province.setProvinceId(resultSet.getInt("id"));
                province.setProvinceName(resultSet.getString("name"));
                provinces.add(province);
            }
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        }finally {
            JdbcUtil.close(connection,ps,resultSet);
        }
        return provinces;

    }

    //查詢省份對應的所有城市
    public List<City> queryCity(Integer provinceId){
        Connection connection = null;
        PreparedStatement ps = null;
        ResultSet resultSet = null;
        City city = null;
        List<City> citys = new ArrayList<>();
        try {
            connection = JdbcUtil.getConnection();
            String sql = "select * from city where provinceid=?";
            ps = connection.prepareStatement(sql);
            ps.setInt(1,provinceId);
            resultSet = ps.executeQuery();
            while (resultSet.next()) {
                city = new City();
                city.setCityId(resultSet.getInt("id"));
                city.setCityName(resultSet.getString("name"));
                citys.add(city);
            }
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        }finally {
            JdbcUtil.close(connection,ps,resultSet);
        }
        return citys;

    }
}

xml：

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="https://jakarta.ee/xml/ns/jakartaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="https://jakarta.ee/xml/ns/jakartaee https://jakarta.ee/xml/ns/jakartaee/web-app_5_0.xsd"
         version="5.0">
    <servlet>
        <servlet-name>QueryProvinceServlet</servlet-name>
        <servlet-class>com.burnyouth.controller.QueryProvinceServlet</servlet-class>
    </servlet>
    <servlet>
        <servlet-name>QueryCityServlet</servlet-name>
        <servlet-class>com.burnyouth.controller.QueryCityServlet</servlet-class>
    </servlet>

    <servlet-mapping>
        <servlet-name>QueryProvinceServlet</servlet-name>
        <url-pattern>/queryProvince</url-pattern>
    </servlet-mapping>
    <servlet-mapping>
        <servlet-name>QueryCityServlet</servlet-name>
        <url-pattern>/queryCity</url-pattern>
    </servlet-mapping>

    <!--設定一下歡迎資源檔案-->
    <welcome-file-list>
        <welcome-file>index.jsp</welcome-file>
    </welcome-file-list>
</web-app>

com.burnyouth.controller.QueryProvinceServlet（回傳 json 格式的省份資訊）：

package com.burnyouth.controller;

import com.burnyouth.dao.QueryProvinceDao;
import com.burnyouth.entity.Province;
import com.fasterxml.jackson.databind.ObjectMapper;
import jakarta.servlet.*;
import jakarta.servlet.http.*;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.List;

public class QueryProvinceServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String json = "";
        QueryProvinceDao dao = new QueryProvinceDao();
        List<Province> provinces = new ArrayList<>();
        PrintWriter out = null;

        provinces = dao.queryProvince();
        //將list轉為json格式的字串
        if (provinces != null) {
            //呼叫Jackson工具庫，實作List ---> json
            ObjectMapper objectMapper = new ObjectMapper();
            json = objectMapper.writeValueAsString(provinces);
        }

        //使客戶端瀏覽器使用正確的編輯器解讀資料
        response.setContentType("application/json;charset=utf-8");
        out = response.getWriter();
        //輸出json資料
        out.write(json);
        out.flush();
        out.close();
    }
}

com.burnyouth.controller.QueryCityServlet（根據客戶端發送過來的省份 id ，回傳對應的城市資訊【json 格式】）：

package com.burnyouth.controller;

import com.burnyouth.dao.QueryProvinceDao;
import com.burnyouth.entity.City;
import com.burnyouth.entity.Province;
import com.fasterxml.jackson.databind.ObjectMapper;
import jakarta.servlet.*;
import jakarta.servlet.http.*;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.List;

public class QueryCityServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String json = "";
        //獲取省份id
        String provinceId = request.getParameter("provinceId");
        QueryProvinceDao dao = new QueryProvinceDao();
        List<City> cities = new ArrayList<>();
        PrintWriter out = null;

        cities = dao.queryCity(Integer.valueOf(provinceId));
        //將list轉為json格式的字串
        if (provinceId != null && !"".equals(provinceId.trim())) {
            //呼叫Jackson工具庫，實作List ---> json
            ObjectMapper objectMapper = new ObjectMapper();
            json = objectMapper.writeValueAsString(cities);
        }

        response.setContentType("application/json;charset=utf-8");
        out = response.getWriter();
        //輸出json資料
        out.write(json);
        out.flush();
        out.close();
    }
}

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