城市：請選擇城市

function changeCity() {
var provinceId = document.getElementById("province").value;
var xmlhttp;
if (window.XMLHttpRequest) {
xmlhttp = new XMLHttpRequest();
} else {
xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
}
xmlhttp.onreadystatechange = function () {
if (xmlhttp.readyState == 4 && xmlhttp.status == 200) {
var citySelect = document.getElementById("city");
citySelect.innerHTML = xmlhttp.responseText;
}
}
xmlhttp.open("GET", "getCity.jsp?provinceId=" + provinceId, true);
xmlhttp.send();
}

<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%><%@ page import="java.sql.*" %><%
String provinceId = request.getParameter("provinceId");
// 建立數據庫連接
Connection conn = null;
PreparedStatement ps = null;
ResultSet rs = null;
try {
Class.forName("com.mysql.jdbc.Driver").newInstance();
conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/db_name", "username", "password");
ps = conn.prepareStatement("SELECT * FROM city WHERE province_id = ?");
ps.setString(1, provinceId);
rs = ps.executeQuery();
StringBuilder sb = new StringBuilder();
while (rs.next()) {
sb.append("" + rs.getString("city_name") + "");
}
out.println(sb.toString());
} catch (Exception e) {
e.printStackTrace();
} finally {
if (rs != null) {
rs.close();
}
if (ps != null) {
ps.close();
}
if (conn != null) {
conn.close();
}
}
%>