java.lang.NumberFormatException: null i
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java.lang.NumberFormatException: null i
提问by user3607180
Here i come up with problem while performing some operation like update,delete and insert but its return some null value with exception kindly some one could look at the code if its wrong:
在这里，我在执行诸如更新、删除和插入之类的操作时遇到了问题，但它返回一些空值，但如果出错，有人可以查看代码：
Error:
错误：
HTTP Status 500 - null
type Exception report
message null
description The server encountered an internal error that prevented it from fulfilling this request.
exception
java.lang.NumberFormatException: null
java.lang.Integer.parseInt(Integer.java:454)
java.lang.Integer.parseInt(Integer.java:527)
Controller.ControllerTest.doGet(ControllerTest.java:48)
javax.servlet.http.HttpServlet.service(HttpServlet.java:617)
javax.servlet.http.HttpServlet.service(HttpServlet.java:723)
note The full stack trace of the root cause is available in the Apache Tomcat/6.0.37 logs.
Apache Tomcat/6.0.37
user.jsp:
用户.jsp：
<form method="POST" action='ControllerTest' name="frmAddUser">
<jsp:useBean id="users" class="java.util.ArrayList" scope="request" />
<% for(int i = 0; i < users.size(); i+=1)
{
UseBean user = (UseBean)users.get(i);
%>
id:<input type="text" name="ID" value="<%=user.getID() %>"><br/>
Name:<input type="text" name="Name" value="<%= user.getName() %>"><br/>
Password:<input type="text" name="password" value="<%= user.getPassword() %>"><br/>
phoneno:<input type="text" name="Phoneo" value="<%= user.getPhoneo() %>"><br/>
Emailid:<input type="text" name="Emailid" value="<%= user.getEmailID() %>"> <br/>
<%} %>
<input type="submit" value="Submit" />
</form>
listuser.jsp
列表用户.jsp
<body>
<table border=1>
<thead>
<tr>
<th>Id</th>
<th>Name</th>
<th>password</th>
<th>phoneno</th>
<th>emailid</th>
<th colspan=2>Action</th>
</tr>
</thead>
<tbody>
<jsp:useBean id="users" class="java.util.ArrayList" scope="request" />
<% for(int i = 0; i < users.size(); i+=1)
{
UseBean user = (UseBean)users.get(i);
%>
<tr>
<td><%= user.getID() %></td>
<td><%= user.getName() %></td>
<td><%= user.getPassword() %></td>
<td><%= user.getEmailID() %></td>
<td><%= user.getPhoneo() %></td>
<td><a href="ControllerTest?action=edit&userId=<%= user.getID() %>" >Update</a></td>
<td><a href="ControllerTest?action=delete&userId=<%= user.getID() %>">Delete</a></td>
</tr>
<% } %>
</tbody>
</table>
<p>
<a href="ControllerTest?action=insert">Add User</a>
</p>
Controllertest.java:
控制器测试.java：
package Controller;
import java.io.IOException;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import dao.UserDao;
import dbBean.UseBean;
public class ControllerTest extends HttpServlet
{
private static final long serialVersionUID = 1L;
private static String INSERT_OR_EDIT = "/user.jsp";
private static String LIST_USER = "/listUser.jsp";
private UserDao dao;
public ControllerTest()
{
super();
dao = new UserDao();
}
protected void doGet(HttpServletRequest request,
HttpServletResponse response) throws ServletException, IOException
{
String forward = "";
String action = request.getParameter("action");
if (action.equalsIgnoreCase("delete"))
{
try
{
int userId = Integer.parseInt(request.getParameter("userId"));
dao.deleteUser(userId);
forward = LIST_USER;
request.setAttribute("users", dao.getAllUsers());
}
catch (NumberFormatException ex)
{
System.out.println("Error occured with during conversion delete");
}
}
else if (action.equalsIgnoreCase("edit"))
{
forward = INSERT_OR_EDIT;
try
{
int userId = Integer.parseInt(request.getParameter("userId"));
UseBean bean = dao.getUserById(userId);
request.setAttribute("user", bean);
} catch (NumberFormatException ex)
{
System.out.println("Error occured with during conversion edit");
}
}
else if (action.equalsIgnoreCase("listUser"))
{
forward = LIST_USER;
request.setAttribute("users", dao.getAllUsers());
} else
{
forward = INSERT_OR_EDIT;
}
RequestDispatcher view = request.getRequestDispatcher(forward);
view.forward(request, response);
}
protected void doPost(HttpServletRequest request,
HttpServletResponse response) throws ServletException, IOException
{
try
{
UseBean bean = new UseBean();
bean.setName(request.getParameter("Name"));
bean.setPassword(request.getParameter("password"));
bean.setPhoneo(request.getParameter("Phoneo"));
bean.setEmailID(request.getParameter("Emailid"));
String userid = request.getParameter("ID");
if (userid == null || userid.isEmpty())
{
dao.addUser(bean);
} else
{
bean.setID(Integer.parseInt(userid));
dao.updateUser(bean);
}
RequestDispatcher view = request.getRequestDispatcher(LIST_USER);
request.setAttribute("users", dao.getAllUsers());
view.forward(request, response);
}
catch (Exception e)
{
e.printStackTrace();
System.out.println("erro occuring in update code");
}
}
}
回答by Jay
You get a NumberFormatException, if you do not pass a valid number to Integer.parseInt()
如果您没有将有效数字传递给 Integer.parseInt()，则会收到 NumberFormatException
int userId = Integer.parseInt(request.getParameter("userid"));
Try to print the value of request.getParameter("userid") and check.
尝试打印 request.getParameter("userid") 的值并检查。
回答by Jagdeep
You're getting a NumberFormatException when trying to convert the empty string "" into an Integer...
尝试将空字符串 "" 转换为整数时，您收到 NumberFormatException ...
回答by Jagdeep
The page you are forwarding on might have some string to integer conversions that might be creating the error
您转发的页面可能有一些字符串到整数的转换，这可能会导致错误
回答by PraveenKumar Lalasangi
Before parsing a string you should do null check and trim then parse. If NumberFormatException occurs handle it.
在解析字符串之前，您应该进行空检查并修剪然后解析。如果发生 NumberFormatException 处理它。
Whenever you get into trouble like this, put debug statements and analyse
what actually causing exception. null or empty or whitespace or string? Then you can handle it easily.
每当遇到这样的麻烦时，请放入调试语句并分析
实际导致异常的原因。null 或空或空格或字符串？然后你可以轻松处理它。
Integer userId= parseToNumber(request.getParameter("userId"));
//check for not null and proceed
// returns null if receivedParam = "", "some string", null or number with space
private Integer parseToNumber(String receivedParam)
{
System.out.println("received param:"+receivedParam);
if (receivedParam != null && !receivedParam.trim().isEmpty())
{
try
{
return Integer.parseInt(receivedParam.trim());
}
catch (NumberFormatException nfe)
{
System.out.println("received param is not a number");
return null;
}
}
else
{
System.out.println("received param is null or empty");
return null;
}
}
回答by Keyur Tarsariya
In file user.jsp and listuser.jsp. you used space for URL Rewriting.
在文件 user.jsp 和 listuser.jsp 中。您使用空间进行 URL 重写。
you should use
你应该使用
<tr>
<td><%=user.getID()%></td>
<td><%=user.getName()%></td>
<td><%=user.getPassword()%></td>
<td><%=user.getEmailID()%></td>
<td><%=user.getPhoneo()%></td>
<td><a href="ControllerTest?action=edit&userId=<%=user.getID()%>" >Update</a></td>
<td><a href="ControllerTest?action=delete&userId=<%=user.getID()%>">Delete</a></td>
</tr>
