こんにちは、被験者のラボを作成できるフォームを作成しようとしています。そのユーザーに関連するサブジェクトを選択できるドロップダウン ボックスがあります。ただし、ページを読み込もうとすると、このエラーが発生しますg.apache.jasper.JasperException: java.lang.NullPointerException。現在使用しているユーザーでは、2 つの結果が必要です。
これが私のサーブレットの完全版です
import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
/**
* Servlet implementation class CreateLab
*/
@WebServlet("/CreateLab")
public class CreateLab extends HttpServlet {
private static final long serialVersionUID = 1L;
/**
* @see HttpServlet#HttpServlet()
*/
public CreateLab() {
super();
// TODO Auto-generated constructor stub
}
int id;
int capacity;
String day = "";
String time = "";
String room = "";
int subject_id;
int user_id;
public void init() {
try {
Class.forName("com.mysql.jdbc.Driver");
Connection con =
DriverManager.getConnection("jdbc:mysql://localhost:3306/wae","root","");
System.out.println("JDBC driver loaded");
}
catch (ClassNotFoundException e) {
System.out.println(e.toString());
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
/**Process the HTTP Get request*/
public void doGet(HttpServletRequest request, HttpServletResponse response) throws
ServletException,IOException {
HttpSession session = request.getSession(true);
String sql = "SELECT id,name" +
" FROM subject " +
" WHERE user_id="+(Integer)session.getAttribute("id");
try{
Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/wae","root","");
System.out.println("connected");
Statement stmt = con.createStatement();
ResultSet res = stmt.executeQuery(sql);
System.out.println(res);
ArrayList<String> list1 = new ArrayList<String>();
ArrayList<String> list2 = new ArrayList<String>();
if (res.next()){
do{
list1.add(res.getString(1));
list2.add(res.getString(2));
System.out.print(list1.add(res.getString(1)));
System.out.print(list2.add(res.getString(2)));
}while(res.next());
System.out.println("Outside");
String[] arr1 = list1.toArray(new String[list1.size()]);
String[] arr2 = list2.toArray(new String[list2.size()]);
System.out.println(list1);
request.setAttribute("res1", arr1);
request.setAttribute("res2", arr2);
request.setAttribute("user_id", user_id);
}
}catch (SQLException e) {
}
catch (Exception e) {
}
sendRegistrationForm(request, response, false);
sendPageHeader(response);
}
/**Process the HTTP Post request*/
public void doPost(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException {
sendPageHeader(response);
HttpSession session = request.getSession(true);
capacity = Integer.parseInt(request.getParameter("capacity"));
day = request.getParameter("day");
time = request.getParameter("time");
room = request.getParameter("room");
user_id = (int) session.getAttribute("id");
subject_id = Integer.parseInt(request.getParameter("subject_id"));
System.out.print(user_id);
boolean error = false;
String message = null;
try {
Class.forName("com.mysql.jdbc.Driver");
Connection con =
DriverManager.getConnection("jdbc:mysql://localhost:3306/wae","root","");
System.out.println("got connection");
System.out.println(id);
Statement s = con.createStatement();
String sql = "SELECT id FROM user" +
" WHERE id='" + user_id + "'";
ResultSet rs = s.executeQuery(sql);
if (rs.next()) {
rs.close();
sql = "INSERT INTO lab" +
" (capacity, day, time, room, subject_id, user_id)" +
" VALUES" +
" ('" + capacity + "'," +
" '" + day + "'," +
" '" + time + "'," +
" '" + room + "','" + subject_id + "','" + user_id + "')";
System.out.println(sql);
int i = s.executeUpdate(sql);
if (i==1) {
message = "Successfully a new lab class.";
response.sendRedirect("Lecturer_labs.jsp");
}
}
s.close();
con.close();
}
catch (SQLException e) {
message = "Error." + e.toString();
error = true;
}
catch (Exception e) {
message = "Error." + e.toString();
error = true;
}
if (message!=null) {
PrintWriter out = response.getWriter();
out.println("<B>" + message + "</B><BR>");
out.println("<HR><BR>");
}
if (error==true)
sendRegistrationForm(request, response, true);
else
sendRegistrationForm(request, response, false);
sendPageFooter(response);
}
}
ここに私のjspページがあります
<%@ 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>Mars University Lab System</title>
<link rel="stylesheet" href="style.css" type="text/css" media="screen">
</head>
<body>
<jsp:include page="headerLecturer.jsp"/>
<tr>
<td>
</td>
</tr>
<tr>
<td>
<div id = "centrecontent">
<br>
<h3>Create Labs</h3>
<%
String[] list1 = (String[])request.getAttribute("res1");
String[] list2 = (String[])request.getAttribute("res2"); %>
<form name ="createLabs" ACTION="CreateLab" method="post">
Capacity: <input type="text" name="capacity"/><br />
Day: <input type="text" name="day"/><br />
Time: <input type="text" name="time"/><br />
Room: <input type="text" name="room"/><br />
<select name="subject_id">
<%
for(int i=0; i<list1.length; i++)
{
out.println("<option value="+list1[0]+"> "+list2[i]+" </option>");
}
%>
</select>
<input type=SUBMIT value="Submit" name="Submit" />
</form>
</div>
<jsp:include page="footer.jsp"/>
</body>
</html>