三、创建Jsp页面：
<%@ page language="java" pageEncoding="gbk"%>
<%@ page import="java.util.*"%>
<%@ page import="com.core.*"%>
<%@ page import="java.sql.*" %>
<%?
??? //获取参数
String times = (request.getParameter("para") == null )? "" : request.getParameter("para") ;
??? List<Integer> timesColl = new ArrayList<Integer>();
??? try{
??????? ConnDB conn = new ConnDB() ;
??????? //当用户传递过来参数不为空时，向数据库插入数据
??????? if(!times.equals("")){
??????????? String sql = "insert into times values('"+times+"')" ;
??????????? //测试
??????????? System.out.println("sql-------->"+sql) ;
??????????? conn.executeUpdate(sql);
??????? }
??????? String sql = "select ti from times" ;
??????? ResultSet rs = conn.executeQuery(sql) ;
??????? while(rs.next()){
??????????? timesColl.add(rs.getInt(1));
??????? }
??????? // 捕获异常
??? }catch(Exception e){
??????? e.printStackTrace() ;
??? }
%>
<html>
? <head>
??? <title>下拉列表+Javascript</title>
??? <meta http-equiv="pragma" content="no-cache">
??? <meta http-equiv="cache-control" content="no-cache">
??? <meta http-equiv="expires" content="0">???
??? <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
??? <meta http-equiv="description" content="This is my page">
? </head>
? <body>
??? <form name = "form1" action="index.jsp" method="post" />
??? 频率：
??? <select name="pl" id="pl" style="width:45px" >
??? <!―动态加载下拉列表的值-->
??? <%for(int i:timesColl){ %>
??????????? <option value="<%=i %>"><%=i %></option>
??????? <%} %>? ? ?
??? </select>
??? <input type="text" size="10" name="times" id="times"> <input type="button" name="b1" id="b1" value="添加" onclick="addtimes();">
??? </form>
??? <script type="text/javascript">
??? function addtimes(){
??? ???? alert("ok") ;
??? ???? //form对象
??? ???? var f = document.getElementById("form1") ;
??? ???? //获取文本值
??? ???? var v = document.getElementById("times").value ;
??? ???? //select对象
??? ???? var sObject = document.getElementById("pl") ;
??? ???? alert(v) ;
??????????? //先判断下拉列表是否已经存在该值??? ????
??? ???? var len = sObject.options.length;
??? ???? alert("select长度--"+len) ;
??? ???? var flag = false ;
??? ???? for(var i=0;i<len;i++){
??? ???????? if(v==sObject.options[i].value){
??? ???????????? alert("存在该值!") ;
??? ???????????? flag = true ;
??? ???????????? //退出循环
??? ???????????? break ;
??? ???????? }
??? ???? }
??? ???? //当文本框的值与要添加的值不相等时，才向更新数据库
??? ???? if(flag==false){
??? ???????? f.action="index.jsp?para="+v ;
??? ???????? f.submit() ;
??? ???? }
??? }
??? </script>
? </body>
</html>