这次给大家带来Ajax与Jquery结合数据库做出实现下拉框的二级联动，Ajax与Jquery结合数据库做出实现下拉框二级联动的注意事项有哪些，下面就是实战案例，一起来看一下。
首先我们需要先建立好数据库，将一些数据插入进去
需要两张表：
province：省份表
city： 城市表
如图：
然后再在java中建立相关的实体类与之对应
再然后，我们就能开始做jdbc的操作了public class ConnectionFactory {
private static String driver;
private static String url;
private static String user;
private static String password;
static {
Properties prop = new Properties();
//读取文件
try {
InputStream in = ConnectionFactory.class.getResourceAsStream("./jdbc.properties");
prop.load(in);
driver = prop.getProperty("jdbc.driver");
url = prop.getProperty("jdbc.url");
user = prop.getProperty("jdbc.user");
password = prop.getProperty("jdbc.password");
} catch (IOException e) {
e.printStackTrace();
}
}
/**
* 获取连接对象
* @return
*/
public static Connection getConnection(){
Connection conn = null;
try {
Class.forName(driver);
conn = DriverManager.getConnection(url, user, password);
} catch (Exception e) {
throw new RuntimeException(e);
}
return conn;
}
/**
* 关闭资源
* @param conn
* @param pstmt
* @param stmt
* @param rs
*/
public static void close(Connection conn,PreparedStatement pstmt,Statement stmt,ResultSet rs){
try {
if (conn != null) {
conn.close();
}
if (pstmt != null) {
pstmt.close();
}
if (stmt != null) {
stmt.close();
}
if (rs != null) {
rs.close();
}
} catch (SQLException e) {
throw new RuntimeException(e);
}
}
首先我们可以在页面加载的时候获取所有省份的信息，SQL语句如下Connection conn = null;
PreparedStatement pstmt = null;
Province province2 = null;
@Override
public ArrayList findAllPro() {
ResultSet rs = null;
ArrayList pros = null;
try {
String sql = "select id,place from province";
conn = ConnectionFactory.getConnection();
pstmt = conn.prepareStatement(sql);
pros = new ArrayList();
rs = pstmt.executeQuery();
while(rs.next()){
Province province = new Province();
province.setId(rs.getInt(1));
province.setPlace(rs.getString(2));
pros.add(province);
}
} catch (SQLException e) {
throw new RuntimeException(e);
}
return pros;
}
将查到的数据放到后台,建立一个SelectedServlet类，用于接收查询到的所有省份的信息response.setContentType("application/json;charset=utf-8");
response.setCharacterEncoding("utf-8");
request.setCharacterEncoding("utf-8");
//创建一个Place对象
ArrayList pros= new Place().findAllPro();
PrintWriter out = response.getWriter();
//将集合直接转换为Json对象
out.write(JSONArray.fromObject(pros).toString());
在这里会用到集合转换Json对象，我们需要导入以下几个包
然后我们开始写前台页面：
省份:
--请选择省份--
城市:
--请选择城市--
然后jQuery代码如下:(由于我导入的jQuery版本比较低，所以使用的方法是getJSON，而不是getJson)$.getJSON("SelectedServlet",function(data,textStatus){
var provinces = data;
var res = "";
for(var i =0;i
res += ""+provinces[i].place+"";
}
$("#province").append(res);
});
这样就能在页面加载的时候获取到数据
然后我们再来做联动，首先给下拉框添加一个change事件，然后获取选中的信息，将选中的信息发送到另一个CityServlet中//下拉框改变时触发的事件
$("#province").change(function(){
var seled = $("option:selected").html();
$("span").html(seled);
$.getJSON("CityServlet",{
"province":encodeURI(encodeURI(seled))
},function(data){
$("#city").html("");
var citys = data;
var res = "";
for(var i = 0;i
res += ""+citys[i].place+"";
}
$("#city").append(res);
});
});
服务器通过获得的信息通过sql语句查询出来，SQL代码如下：public ArrayList findAllCityByPro(String name) {
ResultSet rs = null;
ArrayList citys = null;
try {
//通过名字获得所有值
String sql = "select c.city_place from city c ,"
+ "province p where c.province_id = "
+ " (select id from province where place = '"+ name +"') "
+ " and c.province_id = p.id";
conn = ConnectionFactory.getConnection();
pstmt = conn.prepareStatement(sql);
citys = new ArrayList();
System.out.println(sql);
rs = pstmt.executeQuery();
while(rs.next()){
City city = new City();
city.setPlace(rs.getString(1));
citys.add(city);
}
System.out.println(citys);
} catch (SQLException e) {
e.printStackTrace();
}
return citys;
}
将查询到的数据发送到后台，后台接收到数据后将其转换为Json对象，并通过回调函数发送到前台，然后前台就可以通过事件直接获取到数据，而不用各种跳转页面，这就是Ajax(Asynchronous Javascript And XML),protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("application/json;charset=utf-8");
response.setCharacterEncoding("utf-8");
request.setCharacterEncoding("utf-8");
// String proName = "浙江";
String proName = URLDecoder.decode(URLDecoder.decode(request.getParameter("province"), "utf-8"),
"utf-8");
ArrayList citys= new Place().findAllCityByPro(proName);
PrintWriter out = response.getWriter();
out.write(JSONArray.fromObject(citys).toString());
}
至于显示页面的代码也在前面写到jQuery语句中了
效果如下：
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