CODEWITHSUNDEEP
javajdbcresultset
soad el-hayek
soad el-hayek

Reputation: 63

NullPointerException when using executeQuery

I have a null pointer exception in 

ResultSet rs = aStatement.executeQuery(Query); // it can't be executed

my code is like this :

 public static boolean testLogin(String user, String password) throws SQLException {
    String Query = "select * from TBL_Users where userName = '" + user + "' and  passWord = '" + password + "' ";
    ResultSet rs = aStatement.executeQuery(Query);

    while (rs.next()) {

        info.Id = rs.getInt("ID");
        info.userName = rs.getString("userName");
        info.Name = rs.getString("User_Name");
        info.Password = rs.getString("passWord");
        info.isAdmin = rs.getBoolean("Admin");
        return true;
    }
    return false;
}

}

Upvotes: 0

Views: 1533

Answers (5)

duffymo
duffymo

Reputation: 308753

Sounds like you think aStatement should not be null, but it is.

This is bad JDBC code, for many reasons:

  1. No cleanup of resources.
  2. Doesn't use PreparedStatement
  3. Keeps creating the query string over and over again instead of using a static variable
  4. Doesn't follow Java coding standards ("Query" should be "query")

Here's another way to write it. Start with an interface: 

package persistence;

import java.sql.SQLException;

public interface CredentialDao
{
    boolean isValidUser(String username, String password) throws SQLException;
}

Write an implementation:

package persistence;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

public class CredentialDaoImpl implements CredentialDao
{
    private static final String CREDENTIAL_QUERY = "SELECT COUNT() FROM USER WHERE USERNAME = ? AND PASSWORD = ?";

    private Connection connection;

    public CredentialDaoImpl(Connection connection)
    {
        this.connection = connection;
    }

    public boolean isValidUser(String username, String password) throws SQLException
    {
        boolean isValidUser = false;

        PreparedStatement ps = null;
        ResultSet rs = null;

        try
        {
            ps = this.connection.prepareStatement(CREDENTIAL_QUERY);
            ps.setString(1, username);
            ps.setString(2, password);
            rs = ps.executeQuery();
            while (rs.next())
            {
                int count = rs.getInt(1);
                isValidUser = (count > 0);
            }
        }
        finally
        {
            DatabaseUtils.close(rs);
            DatabaseUtils.close(ps);
        }

        return isValidUser;
    }
}

Upvotes: 6

Jaydee
Jaydee

Reputation: 4158

 while (rs.next()) {

    info.Id = rs.getInt("ID");
    info.userName = rs.getString("userName");
    info.Name = rs.getString("User_Name");
    info.Password = rs.getString("passWord");
    info.isAdmin = rs.getBoolean("Admin");
    return true;       //                                Huh? What?
}

What is info refering to and why is there a return imediatly after the assignments?

Upvotes: 0

Vladimir Ivanov
Vladimir Ivanov

Reputation: 43088

Use prepared statements.

    Connection con = ...; // obtain connection here
    PreparedStatement pstmt = con.prepareStatement("select * from TBL_Users where userName = ?'");
    pstmt.setInt(1, userName);

    ResultSet rs = pstmt .executeQuery();
...
// do clean up here

Upvotes: 0

Christopher Klewes
Christopher Klewes

Reputation: 11435

The aStatement variable is apparently null, please validate that it is correctly set. You should consider read the Java Naming Conventions and make sure you use the lower camel case for variables and java bean conventions.

For code snippets in stackoverflow if they are not self-explanatory, you should obey the rules of the SSCCE, this will help you to get more and better answers. Also you should provide a stack trace with the occured exception.

Upvotes: 1

Jim
Jim

Reputation: 22646

Most likely aStatement is null.

Upvotes: 9

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