我正在尝试从UI中将记录插入MySQL，但我在JSP页面中获得了nullpointerexception。以下是我的文件。
Struts文件
<?xml version="1.0" encoding="ISO-8859-1" ?>
<!DOCTYPE struts-config PUBLIC
"-//Apache Software Foundation//DTD Struts Configuration 1.3//EN"
"http://struts.apache.org/dtds/struts-config_1_3.dtd">
<struts-config>
<action-mappings>
<action
path="/inputemployee"
forward="/pages/inputemployee.jsp"/>
<action path="/db" parameter="method" type="com.pramesh.strutsdatabase.action.DataBaseAction">
<forward name="success" path="/pages/insertsucess.jsp"/>
</action>
</action-mappings>
</struts-config>
inputemployee.jsp文件
<%@taglib uri="http://struts.apache.org/tags-html" prefix="html"%>
<!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=ISO-8859-1">
<title>Insert title here</title>
</head>
<body>
<script >
function calculate(){
document.frm.action="db.html";
var selection=document.frm.sel.selectedIndex
if(selection==1){
document.frm.method.value="insert";
}
document.frm.submit();
}
</script>
<body>
<form name ="frm">
Enter Employee ID :<input name ="Employee ID"/>
Enter Employee First Name :<input name ="First Name"/>
Enter Employee Last Name :<input name ="Last Name"/>
<select name ="sel">
<option>Please Select</option>
<option value="1">Insert</option>
</select>
<input name ="method" type ="hidden" />
<input type ="button" value="Insert" onClick="calculate()"/>
</form>
</body>
</html>
Employee.java
package com.sigma.pojo;
import org.apache.struts.action.ActionForm;
公共类员工{
private int empId;
private String firstName;
private String lastName;
public int getEmpId() {
return empId;
}
public void setEmpId(int empId) {
this.empId = empId;
}
public String getFirstName() {
return firstName;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
}
public String getLastName() {
return lastName;
}
public void setLastName(String lastName) {
this.lastName = lastName;
}
@Override
public String toString() {
return "Employee [empId=" + empId + ", firstName=" + firstName
+ ", lastName=" + lastName + "]";
}
}
EmployeeDAO.java
package com.sigma.employeedDAO;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;
import com.sigma.pojo.Employee;
public class EmployeeDAO {
private Connection con = null;
private java.sql.Statement stmt = null;
private java.sql.PreparedStatement pstmt = null;
private ResultSet rs = null;
private Employee e;
private List <Employee> list= null;
private Connection getConnection(){
if (con==null){
try {
Class.forName("com.mysql.jdbc.Driver");
con=DriverManager.getConnection("jdbc:mysql://localhost:3306/test", "root", "kalokando11");
} catch (ClassNotFoundException | SQLException e) {}
}
return con;
}
public List<Employee> getEmployee(){
list = new ArrayList<Employee>();
try {
stmt = getConnection().createStatement();
rs = stmt.executeQuery("select * from employee");
while(rs.next()){
frm = new Employee();
frm.setEmpId(rs.getInt("emp_id"));
frm.setFirstName(rs.getString("first_name"));
frm.setLastName(rs.getString("last_name"));
list.add(frm);
}
} catch (SQLException e1) {
}
close();
return list;
}
public void insert(Employee e1) throws SQLException{
pstmt = getConnection().prepareStatement("Insert into employee values (?,?,?) ");
pstmt.setInt(1,e1.getEmpId());
pstmt.setString(2, e1.getFirstName());
pstmt.setString(3,e1.getLastName());
pstmt.execute();
close();
}
public void close(){
try {
con.close();
stmt.close();
pstmt.close();
rs.close();
} catch (SQLException e) {
}
}
}
DataBaseAction.java
package com.pramesh.strutsdatabase.action;
import java.sql.SQLException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.apache.struts.action.Action;
import org.apache.struts.action.ActionForm;
import org.apache.struts.action.ActionForward;
import org.apache.struts.action.ActionMapping;
import org.apache.struts.actions.DispatchAction;
import com.sigma.employeedDAO.EmployeeDAO;
import com.sigma.pojo.Employee;
public class DataBaseAction extends DispatchAction{
public ActionForward display(ActionMapping mapping, ActionForm form,
HttpServletRequest request, HttpServletResponse response)
throws Exception {
response.setContentType("text/html");
list =dao.getEmployee();
request.setAttribute("employee", list);
return mapping.findForward("success");
}
public ActionForward insert(ActionMapping mapping, ActionForm form,
HttpServletRequest request, HttpServletResponse response)
throws Exception {
Employee e1 = new Employee();
response.setContentType("text/html");
e1.setEmpId(Integer.parseInt(request.getParameter("Employee ID")));
e1.setFirstName(request.getParameter("First Name"));
e1.setLastName(request.getParameter("Last Name"));
EmployeeDAO dao = new EmployeeDAO();
dao.insert(e1);
return mapping.findForward("success");
}
}
insertsucess.jsp
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<!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=ISO-8859-1">
<title>Insert title here</title>
</head>
<body>
Employee Added
</body>
</html>
listemployee.jsp
<%@page import="java.util.List"%>
<%@page import="com.sigma.pojo.Employee"%>
<%@page import="com.pramesh.strutsdatabase.action.DataBaseAction"%>
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<%@ taglib uri="http://java.sun.com/jsp/jstl/fmt" prefix="fmt"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<body>
<table border=1>
<thead>
<tr>
<th>Employee ID</th>
<th>First Name</th>
<th>Last Name</th>
<th colspan=2>Action</th>
</tr>
</thead>
<tbody>
<c:forEach items="${employee}" var="user">
<tr>
<td><c:out value="${user.empId}" /></td>
<td><c:out value="${user.firstName}" /></td>
<td><c:out value="${user.lastName}" /></td>
</tr>
</c:forEach>
</tbody>
</table>
</body>
</html>
当我调用EmployeeDAO insert 方法时，我得到 NullPointerException 。有人可以解释原因吗？我可以连接到数据库并更新表，但由于NullPointerExection，我无法显示insertsucess页面。