NullPointerException in Java Mysql querying

Question

I'm new to java programming and I'm making a project which implies the use of java and mysql and I cannot manage to fix a NullPointerException in this piece of code, can anyone help me?

here's the full code, the connection part is working fine, its tested

package database;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.util.ArrayList;

import database.mainConnection;

public class userUtils extends mainConnection {

    public static void main(String[] args ) throws Exception {
        userLogin("mattia",hash("password");

    }


    /*public static Boolean registerUser(String name, String surname, String username, String email, String password, String Affiliation, String dateOfBirth) throws Exception {
        Connection con = getConnection();
        // 0000-00-00 format date

        PreparedStatement query = con.prepareStatement("INSERT INTO users (UserID, Username, Email, Password, Name, Surname, BirthDate, Affiliation) VALUES (?,?,?,?,?,?,?,?)");

        query.executeUpdate();
        return false;
    }*/

    public static Boolean userLogin(String username, String password) throws Exception {
        Boolean bool = null;
        try{
            Connection con = getConnection();
            PreparedStatement query = con.prepareStatement("SELECT * FROM users WHERE Username=? AND Password=?");
            query.setString(1, username);
            query.setString(2, password);

            ResultSet result = query.executeQuery();

            if(result.next()) {
                bool = true;
            }

            } catch(Exception e) {
                e.printStackTrace();
                }
        return bool;
    }
}

Also it doesn't give any results back, but i guess its due to the nullpointerexception

the error points at

con.prepareStatement("SELECT * FROM users WHERE Username=? AND Password=?"); and at a printlnine where i invoke the method

Where's the nullpointer? My guess is that `con` is `null` because `getConnection()` returns null — Mark, Nov 27 '18 at 08:21
It's a pity that the exact location of the error is a secret. — glglgl, Nov 27 '18 at 08:22
unfortunately, this is what you get when beginning programmers choose not to learn the basics. You should change: System.out.println(e); to e.printStackTrace(); , show that StackTrace in your question, and show in the code what line it points to. — Stultuske, Nov 27 '18 at 08:23
why does your method signature contains "throws Exception", while it is impossible for your method to throw an Exception? — Stultuske, Nov 27 '18 at 08:24
it is, but i made it return a null because eclipse asks to do so, i picked up the suggestion. i cant locate the nullpointer because it just appears in the catch, thats the big issue, i cant even locate the error — MATTIA PACCAMICCIO, Nov 27 '18 at 08:24
@MATTIAPACCAMICCIO read my first comment, follow those steps, and you should be able to tell on exactly which line it occurs — Stultuske, Nov 27 '18 at 08:25
Rest of the code looks fine this line should be causing Connection con = getConnection(); can u check do u get the connection object — Varun, Nov 27 '18 at 08:26
java.lang.NullPointerException at database.userUtils.userLogin(userUtils.java:32) at database.userUtils.main(userUtils.java:13) — MATTIA PACCAMICCIO, Nov 27 '18 at 08:26
we don't know what line that is, because we don't have your code. All I can see from this bit, is that you don't follow naming conventions — Stultuske, Nov 27 '18 at 08:27
Post the code to getConnection, it is very likely it returns null — Joakim Danielson, Nov 27 '18 at 08:40

score 0 · Answer 1 · answered Nov 27 '18 at 11:01

0

Instead of null assign false to your bool variable, try to use boolean a primitive datatype for return type of class and bool instead of wrapper class Boolean.

      Boolean bool = false;

answered Nov 27 '18 at 11:01

arpita

11
2

score -1 · Answer 2 · edited Nov 27 '18 at 08:42

-1

Boolean bool = null;

or

Connection con = getConnection();

should be the problem.

If the result returns nothing, bool will be null and returned by function.

And check for return of getConnection() is not null.

edited Nov 27 '18 at 08:42

Giorgio

1,973
4
36
51

answered Nov 27 '18 at 08:33

Mehmet Özdemir

1
2

Boolean bool = null; can not possibly be the problem here. The Exception is thrown within that method (in the try block), not from the method calling this method. – Stultuske Nov 27 '18 at 08:44
Yes, you are right but according to what he said about his java knowledge and guess about exception, i thought he may have misunderstood the problem. He said, "here's the full code, the connection part is working fine, its tested" and "Also it doesn't give any results back, but i guess its due to the nullpointerexception". This is why i thought this way. – Mehmet Özdemir Nov 27 '18 at 10:46

NullPointerException in Java Mysql querying

2 Answers2