据我所知，当复选框页面将参数传递到原型(prototype)页面时，原型(prototype)页面将其放入投资组合对象中，然后使用该对象检查数据值并显示投资组合名称，以及当原型(prototype)页面刷新时参数不会再次从复选框页面传递，并且投资组合对象中存储有一个空值，这会导致空指针异常。
因此，如果我在从复选框页面传递参数值后存储参数值，是否可以解决问题？如果是这样我该怎么办？
这是原型(prototype)页面的代码
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<%@ page import="java.io.*"%>
<%@ page import="java.sql.*"%>
<%@ page import="java.util.*"%>
<%@ page import="oracle.jdbc.pool.OracleDataSource"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<head>
<title>Live Data Tracking</title>
<style type='text/css'>
.wrapper {
margin: 0px auto;
width: 1379px;
background-color: #cccccc
}
.header {
float: left;
width: 100%;
background-color: #356aa0
}
.left1 {
float: left;
margin-right: 10px;
width: 338px;
background-color: #ffffff
}
.left2 {
float: left;
margin-right: 10px;
width: 337px;
background-color: #ffffff
}
.left3 {
float: left;
margin-right: 10px;
width: 337px;
background-color: #ffffff
}
.right {
float: right;
width: 337px;
background-color: #ffffff
}
.footer {
float: left;
width: 100%;
background-color: #00457b
}
body {
padding: 0px;
margin: 0px;
font-size: 90%;
background-color: #e7e7de
}
</style>
</head>
<script type="text/javascript">
<%
ArrayList<ArrayList<String>> testList = new ArrayList();
portfolio = request.getParameterValues("portfolio");
try{
OracleDataSource ds= new OracleDataSource();
//javax.sql.DataSource ds = new javax.sql.DataSource();
ds.setDriverType("thin");
ds.setServerName("localhost");
ds.setPortNumber(1521);
ds.setDatabaseName("orcl");
ds.setUser("system");
ds.setPassword("amex1234");
Connection connection = ds.getConnection();
System.out.println("Connected Successfully");
Statement statement = connection.createStatement() ;
if (portfolio!=null)
{
for(int i=0;i<portfolio.length;i++)
testList.add(new ArrayList());
//System.out.println(testList);
for(int i=0; i<portfolio.length;i++)
{ String temp="";
ResultSet resultset = statement.executeQuery("select num FROM "+portfolio[i]+"_Test") ; //Put in SQl command and Table name here
while(resultset.next()){
temp = resultset.getString(1);
testList.get(i).add(temp);
}
//System.out.println(testList);
}
}
} catch(SQLException e) {
e.printStackTrace();
}
%>
</script>
<body>
<%! String[] portfolio; %>
<div class="wrapper">
<div class="header">
<center>
<h4>Live Tracker</h4>
</center>
</div>
<div class="left1">
<h3>Portfolio</h3>
<%
if (portfolio != null)
{
for (int i = 0; i < portfolio.length; i++) //i=portfolio length proxy
{
out.println ("<b>"+portfolio[i]+"<b>"); %>
<br>
<% }
}
else out.println ("<b>none<b>");
%>
</div>
<div class="left2">
<h3>Pre-Stage</h3>
for (int j = 0; j < portfolio.length; j++)
{
response.setIntHeader("Refresh", 2);
//System.out.println(testList.get(j).size());
if (testList.get(j).size()!=0){ %>
Data is there <br>
<% } else { %>
No data <br>
<% }
}%>
</div>
<div class="left3">
<h3>Stage</h3>
</div>
<div class="right">
<h3>Mirror</h3>
</div>
<div class="footer">Something Funny and Witty Here</div>
</div>
</body>
</HTML>
这是复选框页面的代码。通过此页面运行
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<HTML>
<body>
<FORM method="POST" ACTION="Proto_1.jsp">
<center>
Select your portfolio(s): <br><br>
<table>
<tr>
<td>
<input TYPE=checkbox name=portfolio VALUE=X>
</td>
<td>
X
</td>
</tr>
<tr>
<td>
<input TYPE=checkbox name=portfolio VALUE=Y>
</td>
<td>
Y
</td>
</tr>
<tr>
<td>
<input TYPE=checkbox name=portfolio VALUE=W>
</td>
<td>
W
</td>
</tr>
<tr>
<td>
<input TYPE=checkbox name=portfolio VALUE=V>
</td>
<td>
V
</td>
</tr>
<tr>
<td>
<input TYPE=checkbox name=portfolio VALUE=S>
</td>
<td>
S
</td>
</tr>
</table>
<br> <INPUT TYPE=submit name=submit Value="Submit">
</center>
</FORM>
</BODY>
</HTML>
最佳答案
有几个选项需要解决。
选项 1:将参数设置到 session 中。而不是:
portfolio = request.getParameterValues("portfolio");
试试这个:
String[] portfolio = null;
if(null == request.getParameter("submit")) { //page reload, true
portfolio = (String[])session.getAttribute("portfolio");
} else {
portfolio = request.getParameterValues("portfolio");
session.setAttribute("portfolio", portfolio);
}
选项 2:将 View 和业务逻辑分开，即将页面分成两部分。第一个 jsp 从请求中获取portfolio，并频繁调用以从第二个 jsp 获取更新的记录。此方法需要 JavaScript。
View.jsp:使用setInterval()频繁调用Records.jsp
<script>
var getRecords = function() {
// to do here
};
setInterval(getRecords, 2 * 1000); (in miliseconds)[every 2 sec]
</script>
Records.jsp:生成动态 html 和记录
关于java - 刷新 JSP 页面时出错，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/31136551/