这里我提出了像更新，删除和查看这样的操作的问题，所以现在插入工作正常，但其他操作如update，delete，view显示错误，如。有人可以指导正确的方向吗？这就是我到现在为止所做的一切
HTTP Status 500 - java.lang.NullPointerException
type Exception report
message java.lang.NullPointerException
description The server encountered an internal error that prevented it from fulfilling this request.
exception
javax.servlet.ServletException: java.lang.NullPointerException
org.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:515)
org.apache.struts2.dispatcher.FilterDispatcher.doFilter(FilterDispatcher.java:419)
root cause
java.lang.NullPointerException
Action.Testiue.view(Testiue.java:115)
sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
java.lang.reflect.Method.invoke(Method.java:606)
com.opensymphony.xwork2.DefaultActionInvocation.invokeAction(DefaultActionInvocation.java:404)
com.opensymphony.xwork2.DefaultActionInvocation.invokeActionOnly(DefaultActionInvocation.java:267)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:229)
com.opensymphony.xwork2.interceptor.DefaultWorkflowInterceptor.doIntercept(DefaultWorkflowInterceptor.java:221)
com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:86)
com.opensymphony.xwork2.DefaultActionInvocation$2.doProfiling(DefaultActionInvocation.java:224)
com.opensymphony.xwork2.DefaultActionInvocation$2.doProfiling(DefaultActionInvocation.java:223)
com.opensymphony.xwork2.util.profiling.UtilTimerStack.profile(UtilTimerStack.java:455)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:221)
com.opensymphony.xwork2.validator.ValidationInterceptor.doIntercept(ValidationInterceptor.java:150)
org.apache.struts2.interceptor.validation.AnnotationValidationInterceptor.doIntercept(AnnotationValidationInterceptor.java:48)
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE struts PUBLIC
"-//Apache Software Foundation//DTD Struts Configuration 2.0//EN"
"http://struts.apache.org/dtds/struts-2.0.dtd">
<struts>
<include file="struts-default.xml" />
<package name="a" extends="struts-default">
<action name="adduser" class="Action.Testiue" method="add">
<result name="success">/insert.jsp</result>
<result name="success">/ssuccess.jsp</result>
</action>
<action name="viewuser" class="Action.Testiue" method="view">
<result name="success">/view.jsp</result>
<result name="error">/error.jsp</result>
</action>
<action name="updateuser" class="Action.Testiue" method="update">
<result name="success">/edit.jsp</result>
<result name="error">/error.jsp</result>
</action>
<action name="deleteuser" class="Action.Testiue" method="delete">
<result name="success">/dsuccess.jsp</result>
<result name="error">/error.jsp</result>
</action>
</package>
</struts>
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" id="WebApp_ID" version="2.5">
<filter>
<filter-name>struts2</filter-name>
<filter-class>org.apache.struts2.dispatcher.FilterDispatcher</filter-class>
</filter>
<filter-mapping>
<filter-name>struts2</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
<welcome-file-list>
<welcome-file>index.jsp</welcome-file>
</welcome-file-list>
</web-app>
package Action;
import com.opensymphony.xwork2.ActionSupport;
import dao.UserDao;
import dbBean.UseBean;
public class Testiue
{
private String Name;
private String Password;
private String EmailID;
private String Phoneo;
private int ID;
public String getName()
{
return Name;
}
public void setName(String name)
{
Name = name;
}
public String getPassword()
{
return Password;
}
public void setPassword(String password)
{
Password = password;
}
public String getEmailID()
{
return EmailID;
}
public void setEmailID(String emailID)
{
EmailID = emailID;
}
public String getPhoneo()
{
return Phoneo;
}
public void setPhoneo(String phoneo)
{
Phoneo = phoneo;
}
public int getID()
{
return ID;
}
public void setID(int i)
{
ID = i;
}
@Override
public String toString()
{
return "UseBean [id=" + ID + ", Name=" + Name+ ", Password=" + Password + ", EmailID=" + EmailID + ", Phoneo="+ Phoneo + "]";
}
private UserDao dao;
private UseBean bean;
public String add()
{
dao=new UserDao();
bean=new UseBean();
System.out.println(getName()+""+getPassword()+""+getPhoneo()+""+getEmailID());
bean.setID(ID);
bean.setName(Name);
bean.setPassword(Password);
bean.setPhoneo(Phoneo);
bean.setEmailID(EmailID);
dao.addUser(bean);
return ActionSupport.SUCCESS;
}
public String update()
{
dao=new UserDao();
bean=new UseBean();
//System.out.println(getName()+""+getPassword()+""+getPhoneo()+""+getEmailID());
bean.setID(ID);
bean.setName(Name);
bean.setPassword(Password);
bean.setPhoneo(Phoneo);
bean.setEmailID(EmailID);
dao.updateUser(bean);
return ActionSupport.SUCCESS;
}
public String delete()
{
int userId =0;
dao.deleteUser(userId);
return ActionSupport.SUCCESS;
}
public String edit()
{
int userId =0;
bean = dao.getUserById(userId);
return ActionSupport.SUCCESS;
}
public String view()
{
dao.getAllUsers();
return ActionSupport.SUCCESS;
}
}
<META HTTP-EQUIV="Refresh" CONTENT="0;URL=viewuser.action">
<%@ taglib prefix="s" uri="/struts-tags"%>
<%@page import="java.util.*,dbBean.*,Dbconnect.*,java.util.*"%>
<a href="<s:url action="adduser.action"/>">Insert</a>
<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>
<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);
%>
<tbody>
<tr>
<td><%= user.getID() %></td>
<td><%= user.getName() %></td>
<td><%= user.getPassword() %></td>
<td><%= user.getEmailID() %></td>
<td><%= user.getPhoneo() %></td>
<td><a href="<s:url action="updateuser.action"/>">Update</a></td>
<td><a href="<s:url action="delete.action"/>">Delete</a></td>
</tr>
<%
}
%>
</tbody>
</table>
<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
<form action="updateuser">
id:<input type="text" name="ID" ><br/>
Name:<input type="text" name="Name" ><br/>
Password:<input type="text" name="password" ><br/>
phoneno:<input type="text" name="Phoneo" ><br/>
Emailid:<input type="text" name="Emailid" > <br/>
<input type="submit" value="Submit" />
</form>
</body>
</html>
package dao;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;
import java.util.List;
import dbBean.UseBean;
import Dbconnect.*;
public class UserDao
{
private Connection conn;
public UserDao()
{
conn=Dbconnect.getConnection();
}
public void addUser(UseBean bean)
{
try
{
String sql="insert into senthil (name,pass,phoneno,emailid) values(?,?,?,?)";
PreparedStatement ps=conn.prepareStatement(sql);
ps.setString(1,bean.getName());
ps.setString(2,bean.getPassword());
ps.setString(3,bean.getPhoneo());
ps.setString(4,bean.getEmailID());
ps.executeUpdate();
}
catch (Exception e)
{
// TODO: handle exception
}
}
public void deleteUser(int userId)
{
try
{
PreparedStatement ps = conn.prepareStatement("delete from senthil where id=?");
// Parameters start with 1
ps.setInt(1, userId);
ps.executeUpdate();
} catch (SQLException e)
{
e.printStackTrace();
}
}
public void updateUser(UseBean bean)
{
try
{
PreparedStatement preparedStatement = conn.prepareStatement("update senthil set name=?, pass=?, phoneno=?, emailid=?"+ "where id=?");
// Parameters start with 1
preparedStatement.setString(1, bean.getName());
preparedStatement.setString(2, bean.getPassword());
preparedStatement.setString(3, bean.getPhoneo());
preparedStatement.setString(4, bean.getEmailID());
preparedStatement.setInt(5, bean.getID());
preparedStatement.executeUpdate();
}
catch (SQLException e)
{
e.printStackTrace();
}
}
public List<UseBean> getAllUsers()
{
List<UseBean> users = new ArrayList<UseBean>();
try
{
Statement statement = conn.createStatement();
ResultSet rs = statement.executeQuery("select * from senthil");
while (rs.next())
{
UseBean user = new UseBean();
user.setID(rs.getInt("id"));
user.setName(rs.getString("name"));
user.setPassword(rs.getString("pass"));
user.setPhoneo(rs.getString("phoneno"));
user.setEmailID(rs.getString("emailid"));
users.add(user);
}
}
catch (SQLException e)
{
e.printStackTrace();
}
return users;
}
public UseBean getUserById(int userId)
{
UseBean user = new UseBean();
try
{
PreparedStatement preparedStatement = conn.prepareStatement("select * from senthil where id=?");
preparedStatement.setInt(1, userId);
ResultSet rs = preparedStatement.executeQuery();
if (rs.next())
{
user.setID(rs.getInt("id"));
user.setName(rs.getString("name"));
user.setPassword(rs.getString("pass"));
user.setPhoneo(rs.getString("phoneno"));
user.setEmailID(rs.getString("emailid"));
}
} catch (SQLException e)
{
e.printStackTrace();
}
return user;
}
}
答案 0 :(得分：0)
在内部视图方法中，您尚未初始化dao对象（即引用为null），请添加以下代码：
在TestIUE.java中再添加一个成员变量：
List<UseBean> users = new ArrayList<UseBean>();
还添加Accessor方法：
public List<UseBean> getUsers()
{
return users;
}
现在修改您的视图方法，如下所示：
public String view()
{
dao = new UseDao();
users = dao.getAllUsers();
return ActionSupport.SUCCESS;
}
答案 1 :(得分：0)
在JSP中，users应该可用于请求范围。
public String view() {
UserDao userDao = new UserDao();
List<UseBean> users = userDao.getAllUsers();
ServletActionContext.getRequest().setAttribute("users", users);
return Action.SUCCESS;
}
public String update() {
UserDao dao = new UserDao();
UseBean bean=new UseBean();
HttpServletRequest request ServletActionContext.getRequest();
bean.setID(request.getParameter("ID");
bean.setName(request.getParameter("Name");
bean.setPassword(request.getParameter("Password");
bean.setPhoneo(request.getParameter("Phoneo");
bean.setEmailID(request.getParameter("EmailID");
//System.out.println(getName()+""+getPassword()+""+getPhoneo()+""+getEmailID());
dao.updateUser(bean);
return Action.SUCCESS;
}
public String delete() {
HttpServletRequest request ServletActionContext.getRequest();
int userId = request.getParameter("ID");
dao.deleteUser(userId);
return Action.SUCCESS;
}
删除操作
<a href="<s:url action="delete"><s:param name='ID'><%=user.getID()%></s:param></s:url>">Delete</a>