异常 org.apache.jasper.JasperException：java.lang.NullPointerException 根本原因 java.langullException.N
[英]exception org.apache.jasper.JasperException: java.lang.NullPointerException root cause java.lang.NullPointerException
问题描述
Everytime I run this jsp I get the following error exception:
每次我运行这个 jsp 时，我都会收到以下错误异常：
org.apache.jasper.JasperException: java.lang.NullPointerException
root cause
java.lang.NullPointerException
Here is my code:这是我的代码：
<%@page import="Business.Account"%>
<%@page contentType="text/html" pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<title>Account Summary Page CHATTA</title>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<style>
body {background-color: powderblue;}
h1 {color: blue;}
p {color: red;}
div {text-align-center;}
</style>
</head>
<%
Account a1 = (Account)session.getAttribute("a1");
%>
<h1 align="center"> CHATTABANK SUMMARY</h1>
<br>
</br>
<form>
<div>
<label for="AcctNo">Accnt ID:</label>
<input type="text" name ="AccntNo" value="<%=a1.getAcctNo()%>"/></br>
<label for="CustID">Cust ID:</label>
<input type="text" name="CUSTID" value="<%=a1.getCid()%>"/></br>
<label for="Type">Type: </label>
<input type="text" name="Type" value="<%=a1.getType()%>"/></br>
<label for="Balance">Balance:</label>
<input type="text" name="Balance" value="<%=a1.getBalance()%>"/></br>
</div>
<div>
<input type="submit" name="subBtn" value="lookup"/>
<input type="reset" name="rstBtn" value="clear"/>
</form>
</html>
Let me know, if any more code is required.如果需要更多代码，请告诉我。
1 个解决方案
解决方案1
0 2019-10-19 20:22:03
You should handle the case where the session does not contain the attribute "a1" to avoid potential NullPointerExceptions calling methods on a null Account reference.您应该处理 session 不包含属性“a1”的情况，以避免潜在的 NullPointerExceptions 调用 null 帐户引用上的方法。 After you retrieve the "a1" attribute, you should also check that the object is actually a Business.Account object to prevent class cast related exceptions.检索“a1”属性后，还应检查 object 实际上是 Business.Account object 以防止与 class 转换相关的异常。
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