用ajax三级联动写一个关于省市区下拉列表的联动
数据库中的表：
id是这条数据的主键，dname是地区名称，parentid是父级id
页面效果：
先实例化一个district类
package com.hanqi.model;
public class District {
private String id;
private String dname;
private String parentid;
public District(String id, String dname, String parentid) {
super();
this.id = id;
this.dname = dname;
this.parentid = parentid;
}
public District() {
super();
// TODO Auto-generated constructor stub
}
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public String getDname() {
return dname;
}
public void setDname(String dname) {
this.dname = dname;
}
public String getParentid() {
return parentid;
}
public void setParentid(String parentid) {
this.parentid = parentid;
}
}
连接数据库
package com.hanqi.util;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
public class DBHelper {
private static final String USERNAME = "test0315";
private static final String PASSWORD = "123456";
private static final String URL = "jdbc:oracle:thin:@localhost:1521:xe";
private static final String CLASSNAME = "oracle.jdbc.OracleDriver";
static {
try {
Class.forName(CLASSNAME);
} catch (ClassNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
public static Connection getConnection() {
Connection conn = null;
try {
conn = DriverManager.getConnection(URL, USERNAME, PASSWORD);
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return conn;
}
public static void destroy(Connection conn,PreparedStatement ps,ResultSet rs) {
if(rs != null) {
try {
rs.close();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
rs = null;
}
if(conn != null) {
try {
conn.close();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
conn = null;
}
if(ps != null) {
try {
ps.close();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
ps = null;
}
}
public static void main(String[] args) {
System.out.println(getConnection());
}
}
数据库访问对象
package com.hanqi.dao;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;
import javax.security.auth.Destroyable;
import com.hanqi.model.District;
import com.hanqi.util.DBHelper;
public class Basedao {
private Connection conn;
private PreparedStatement ps;
private ResultSet rs;
private ResultSet initQuery(String sql, Object... objects) throws SQLException {
conn = DBHelper.getConnection();
ps = conn.prepareStatement(sql);
setParam(ps, objects);
return ps.executeQuery();
}
private void setParam(PreparedStatement ps, Object[] objects) throws SQLException {
int i = 1;
for (Object o : objects) {
ps.setObject(i, o);
i++;
}
}
public List<District> selectdistrict(String parentid) throws SQLException {
List<District> list = new ArrayList<>();
String sql = "select * from c_district where parentid = ?";
rs = initQuery(sql, parentid);
while (rs.next()) {
District dt = new District();
dt.setId(rs.getString("id"));
dt.setDname(rs.getString("dname"));
dt.setParentid(rs.getString("parentid"));
list.add(dt);
}
DBHelper.destroy(conn, ps, rs);
return list;
}
}
servlet类
package com.hanqi.servlet;
import java.io.IOException;
import java.sql.SQLException;
import java.util.List;
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 com.alibaba.fastjson.JSONObject;
import com.hanqi.dao.Basedao;
import com.hanqi.model.District;
/**
* Servlet implementation class FindServlet
*/
@WebServlet("/FindServlet")
public class FindServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
public FindServlet() {
super();
// TODO Auto-generated constructor stub
}
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
String parentid = request.getParameter("parentid");
request.setCharacterEncoding("utf-8");
response.setCharacterEncoding("utf-8");
response.setContentType("text/html;charset:utf-8");
Basedao bd = new Basedao();
JSONObject jo = new JSONObject();
List<District> list = null;
try {
list = bd.selectdistrict(parentid);
} catch (SQLException e) {
e.printStackTrace();
}
if (list != null && list.size() > 0) {
jo.put("success", true);
jo.put("result", list);
} else {
jo.put("seccess", false);
}
response.getWriter().write(jo.toJSONString());
}
protected void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
// TODO Auto-generated method stub
doGet(request, response);
}
}
JSP页面
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<script type="text/javascript" src="js/jquery-3.3.1.min.js"></script>
<script type="text/javascript" src="js/index.js"></script>
<title>Insert title here</title>
</head>
<body>
省:<select id="province">
<option>===请选择===</option>
</select>
市:<select id="city">
<option>===请选择===</option>
</select>
区:<select id="area">
<option>===请选择===</option>
</select>
</body>
</html>
JS页面
$(function() {//$() 此方法代表当JSP页面元素全部加载完成后再执行JS脚本
$.ajax({//ajax方法调用，通过此方法接收前端信息发往后台并接受后台信息显示在前端
type : "post",//发送请求的方式：post/get
url : "FindServlet",//接收请求的地址
dataType : "json",//接收后台数据的类型：text，html，json，xml
data:{//这个ajax请求所携带的参数，是指前端的数据请求，以键值对方式存储，为可选项；
parentid:"0"
},
success : function(data) {//当这个请求成功发送到后台时执行的方法，这里的data参数是指后台响应后发送来的字符串类型的数据；
if (data.success) {//
for (var i = 0; i < data.result.length; i++) {
var district = data.result[i];//将数据里的对象遍历取出
$("#province").append(//添加下拉选项
"<option value=‘" + district.id + "‘>"//将id作为选项的值
+ district.dname + "</option>");
}
}
},
error : function(msg) {//请求失败时执行的方法；
}
});
$("#province").change(//当该选择器改变时执行该方法
function() {//封装一个方法
var provinceid = $(this).val();//获取该选项的值作为请求参数，this代表这个选择器；
$.ajax({
type : "post",
url : "FindServlet",
data : {
parentid : provinceid
},
dataType : "json",
success : function(data) {
if (data.success) {
$("#city").empty();//先将次级选项初始化，再添加下拉数据
$("#city").append("<option>==请选择==</option>");
$("#area").empty();
$("#area").append("<option>===请选择===</option>");
for (var i = 0; i < data.result.length; i++) {
var district = data.result[i];
$("#city").append(
"<option value=‘" + district.id + "‘>"
+ district.dname + "</option>");
}
} else {//如果查询不到数据也要对选项初始化，即清空
$("#city").empty();
$("#city").append("<option>==请选择==</option>");
$("#area").empty();
$("#area").append("<option>===请选择===</option>");
}
},
error : function() {
}
});
});
$("#city").change(
function(){
var cityid = $(this).val();
$.ajax({
type :"post",
url:"FindServlet",
data:{
parentid:cityid
},
dataType:"json",
success:function(data){
if(data.success){
$("#area").empty();
$("#area").append("<option>===请选择===</option>");
for(var i = 0;i<data.result.length;i++){
var district = data.result[i];
$("#area").append
("<option value=‘"+ district.id+"‘ >"+district.dname+"</option>")
}
}else{
$("#area").empty();
$("#area").append("<option>===请选择===</option>");
}
},
error:function(msg){
alert("查询错误！");
}
});
}
);
});
原文：https://www.cnblogs.com/wyc1991/p/9164980.html