NullPointerException when trying to connect to a MySQL Database

[AllenB]

Hello,
I am trying to insert values from a .csv file into a MySQL database from a GUI. I cannot seem to accomplish this. I keep getting a null pointer exception where I set the connection properties in my main method. I also cannot seem to figure out how to use the importData() method after setting my variables in my GUI. I currently have that method called in the main method. I would appreciate any help anyone can give me. Thank you. Here is my code:

import java.awt.*;
import java.util.*;
import javax.swing.*;
import java.sql.*;
import java.lang.Object;

public class ImportDataGUI extends javax.swing.JFrame {

   String nameOfFile;
   String tableName;
   static ImportDataGUI db;
   //Connection conn = db.connect("jdbc:mysql://localhost:3306/Registrar","root","Alyssa01");

    /** Creates new form ImportDataGUI */
    public ImportDataGUI() {
        initComponents();
    }

    /** This method is called from within the constructor to
     * initialize the form.
     * WARNING: Do NOT modify this code. The content of this method is
     * always regenerated by the Form Editor.
     */
    @SuppressWarnings("unchecked")
    // <editor-fold defaultstate="collapsed" desc="Generated Code">
    private void initComponents() {

        tableLabel = new javax.swing.JLabel();
        tableTextField = new javax.swing.JTextField();
        fileLabel = new javax.swing.JLabel();
        fileTextField = new javax.swing.JTextField();
        fileSubmitButton = new javax.swing.JButton();

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);

        tableLabel.setFont(new java.awt.Font("Verdana", 0, 11)); // NOI18N
        tableLabel.setText("Enter the table name below:");

        fileLabel.setFont(new java.awt.Font("Verdana", 0, 11)); // NOI18N
        fileLabel.setText("Enter the file name to import below:");

        fileSubmitButton.setFont(new java.awt.Font("Verdana", 0, 11)); // NOI18N
        fileSubmitButton.setText("Submit");
        fileSubmitButton.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                fileSubmitButtonActionPerformed(evt);
            }
        });

        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addContainerGap()
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.TRAILING, false)
                    .addComponent(fileSubmitButton, javax.swing.GroupLayout.Alignment.LEADING, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                    .addComponent(tableTextField, javax.swing.GroupLayout.Alignment.LEADING)
                    .addComponent(fileLabel, javax.swing.GroupLayout.Alignment.LEADING, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                    .addComponent(tableLabel, javax.swing.GroupLayout.Alignment.LEADING, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                    .addComponent(fileTextField, javax.swing.GroupLayout.Alignment.LEADING))
                .addContainerGap(javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE))
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addContainerGap()
                .addComponent(tableLabel)
                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
                .addComponent(tableTextField, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.UNRELATED)
                .addComponent(fileLabel, javax.swing.GroupLayout.PREFERRED_SIZE, 22, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addGap(9, 9, 9)
                .addComponent(fileTextField, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.UNRELATED)
                .addComponent(fileSubmitButton)
                .addContainerGap(23, Short.MAX_VALUE))
        );

        pack();
    }// </editor-fold>

    private void fileSubmitButtonActionPerformed(java.awt.event.ActionEvent evt) {
        nameOfFile = fileTextField.getText();
        tableName = tableTextField.getText();
        
    }

    /**
    * @param args the command line arguments
    */

    public void importData(Connection conn,String filename) {
        Statement stmt;

        filename = nameOfFile;

        try
        {
            String query = "";
            stmt = conn.createStatement(
            ResultSet.TYPE_SCROLL_SENSITIVE,
            ResultSet.CONCUR_UPDATABLE);
            if (tableName.equals("student")){
            query = "LOAD DATA INFILE '+filename+' INTO TABLE student  FIELDS TERMINATED BY ',' (StudentID,FirstName,LastName,DegreeProgram, Gender)";
            }//end if
            else if(tableName.equals("enrollment")){
            query = "LOAD DATA INFILE '+filename+' INTO TABLE enrollment  FIELDS TERMINATED BY ',' (StudentID, CourseID, Semester)";
            }//end else if
            else if(tableName.equals("course")){
            query = "LOAD DATA INFILE '+filename+' INTO TABLE course  FIELDS TERMINATED BY ',' (courseID,courseName,section,Instructor)";
            }//end else if
            else {
                JOptionPane.showMessageDialog(null,"Invalid entry.");
            }

            stmt.executeUpdate(query);

        }
        catch(Exception e)
        {
            e.printStackTrace();
            stmt = null;
        }
    }//end importData



   public Connection connect(String db_connect_str,String db_userid, String db_password){
        Connection conn;
        try
        {
            Class.forName("com.mysql.jdbc.Driver").newInstance();

         conn = DriverManager.getConnection(db_connect_str, db_userid, db_password);

        }
        catch(Exception e)
        {
            e.printStackTrace();
            conn = null;
        }

        return conn;
    }




    public static void main(String args[]) {
        
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new ImportDataGUI().setVisible(true);
            }
        });
        Connection conn = db.connect("jdbc:mysql://localhost:3306/Registrar","root","Alyssa01");
        db.importData(conn,args[0]);
    }

    // Variables declaration - do not modify
    private javax.swing.JLabel fileLabel;
    private javax.swing.JButton fileSubmitButton;
    private javax.swing.JTextField fileTextField;
    private javax.swing.JLabel tableLabel;
    private javax.swing.JTextField tableTextField;
    // End of variables declaration

}//end ImportDataGUI

[stephen84s]

Using the "root" account for MySQL for normal tasks is not recommended and definitely not a good idea to publish its password on a public forum.

Also can you give us the exact stack trace what exception you are getting.

[Ezzaral]

You're getting the null pointer because you have declared the "db" variable, but you have not initialized it in main().

[prashant yadu]

Hello,
First thing i need to clear is that i am not a gud user of Swing, but i used to connect with database so many times to access data.
The reason for geting Nuill pointer Exception is that u r not providing correct information for data base connectivity. some steps to follow.
1) load the driver class for mysql
com.mysql.jdbc.Driver
2)then create the object of it using url
(" jdbc:mysql://localhost:UrDBName:","username","password");
if u dont know localhost name and username,password, then check it into mysql files to get it.

[Ezzaral]

prashant, that is not the reason for his null pointer. The null pointer exception is from calling methods on his "db" class variable when he has not initialized it.

public static void main(String args[]) {
        
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new ImportDataGUI().setVisible(true);
            }
        });
        [B]// 'db' is still null here[/B]
        Connection conn = [B]db.connect[/B]("jdbc:mysql://localhost:3306/Registrar","root","Alyssa01");
        [B]db.importData[/B](conn,args[0]);
    }