Thread: Problem with running the downloaded jsp program

Greetings and Regards
I downloaded the simple project as an exercise from the github site, I opened the project with eclipse, and I created the database and its table in mysql, and I also made the settings related to the connection to the database, but the project gives an error when running. Please run the program yourself once and give guidance. In terms of coding and programming logic, everything is correct, only an unknown problem occurs in the implementation.
Thanks.
Link of project:
github.com/bhiapp4/crudApp

gives an error

Please copy the full text of the error message and paste it here. It has important info about the error.

java.lang.NullPointerException
com.junald.dao.StudentDAOImplementation.getAllStud ents(StudentDAOImplementation.java:68)
com.junald.controller.StudentController.doGet(Stud entController.java:46)

What variable on line 68 has a null value?

If that is line 68, then the conn variable must have a null value. Check the code that assigns a value to conn to see if it is executed properly.

But the value for this variable is set

Does conn have a non-null value when line 68 is executed? How do you know that?

Sorry, I am not setup for executing JSP code.

Please Post the code that shows where conn is declared, assigned a value and used causing the NPE.

The StudentDAOImplementation class writes errors to the log. Are there any messages there?

StudentDaoImpl.java code:

package com.app.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 com.app.model.Student;
import com.app.util.DBConnectionUtility;
 
public class StudentDaoImpl implements StudentDao{
 
	@Override
	public void addStudent(Student student) {
		try(Connection conn = DBConnectionUtility.getDBConnection()) {			
			String query = "insert into student (firstName, lastName, course, year) values (?,?,?,?)";
			PreparedStatement preparedStatement = conn.prepareStatement(query);
			preparedStatement.setString(1, student.getFirstName());
			preparedStatement.setString(2, student.getLastName());
			preparedStatement.setString(3, student.getCourse());
			preparedStatement.setInt(4, student.getYear());
			preparedStatement.executeUpdate();
		} catch (SQLException e) {
			e.printStackTrace();
		}
	}
 
	@Override
	public void deleteStudent(int studentId) {
		try(Connection conn = DBConnectionUtility.getDBConnection()) {			
			String query = "delete from student where studentId=?";
			PreparedStatement preparedStatement = conn.prepareStatement(query);
			preparedStatement.setInt(1, studentId);
			preparedStatement.executeUpdate();
		} catch (SQLException e) {
			e.printStackTrace();
		}
	}
 
	@Override
	public void updateStudent(Student student) {
		try(Connection conn = DBConnectionUtility.getDBConnection()) {			
			String query = "update student set firstName=?, lastName=?, course=?, year=? where studentId=?";
			PreparedStatement preparedStatement = conn.prepareStatement(query);
			preparedStatement.setString(1, student.getFirstName());
			preparedStatement.setString(2, student.getLastName());
			preparedStatement.setString(3, student.getCourse());
			preparedStatement.setInt(4, student.getYear());
			preparedStatement.setInt(5, student.getStudentId());
			preparedStatement.executeUpdate();
		} catch (SQLException e) {
			e.printStackTrace();
		}
	}
 
	@Override
	public List<Student> getAllStudents() {
		List<Student> students = new ArrayList<Student>();
		try(Connection conn = DBConnectionUtility.getDBConnection()) {			
			Statement statement = conn.createStatement();
			ResultSet resultSet = statement.executeQuery("select * from student");
			while (resultSet.next()) {
				Student student = new Student();
				student.setStudentId(resultSet.getInt("studentId"));
				student.setFirstName(resultSet.getString("firstName"));
				student.setLastName(resultSet.getString("lastName"));
				student.setCourse(resultSet.getString("course"));
				student.setYear(resultSet.getInt("year"));
				students.add(student);
			}
		} catch (SQLException e) {
			e.printStackTrace();
		} catch (Exception e) {
			e.printStackTrace();
		}
		return students;
	}
 
	@Override
	public Student getStudentById(int studentId) {
		Student student = new Student();
		try(Connection conn = DBConnectionUtility.getDBConnection()) {			
			String query = "select * from student where studentId=?";
			PreparedStatement preparedStatement = conn.prepareStatement(query);
			preparedStatement.setInt(1, studentId);
			ResultSet resultSet = preparedStatement.executeQuery();
			while (resultSet.next()) {
				student.setStudentId(resultSet.getInt("studentId"));
				student.setFirstName(resultSet.getString("firstName"));
				student.setLastName(resultSet.getString("LastName"));
				student.setCourse(resultSet.getString("course"));
				student.setYear(resultSet.getInt("year"));
			}
		} catch (SQLException e) {
			e.printStackTrace();
		}
		return student;
	}
}

try(Connection conn = DBConnectionUtility.getDBConnection()) {

What does that code do? Does it return a non-null value to the conn variable?

Please edit your post and wrap your code with code tags:

[code]
**YOUR CODE GOES HERE**
[/code]

to get highlighting and preserve formatting.

Does the call to DBConnectionUtility.getDBConnection() return a valid value for conn?

Why did you post the code for the DBUtil class?
What code calls the getConnection method in the DBUtil class?

Sorry, I can not run your code.

Can you answer my questions about the conn variable? Does it get assigned a non-null value?
Are there any error messages in the server's log files?

Your problem may be with configuring tomcat and the database. I don't know how to do that.
There may be people on this forum that know:
https://coderanch.com/forums
Try asking your question there.

The problem was solved!
The problem was with the driver version of the mysql program, which was older than my version 8 of my sql, which was solved by updating the driver file connection problem with the database.
Thank you

Ok, I am glad you fixed it. Thanks for letting us know what the fix was.