Nullpointerexception when trying to log into the system inside netbeans

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Soon after I did some icon overwrites on the main screen and on the About screen, error occurred NullPointerException, I have no idea how to continue and continue the course I am doing. I use Mysql, and there everything is right, it was after changing the same icons. Follow the code below, Error Print: erro

package br.com.infox.telas;

import java.sql.*;
import br.com.infox.dal.ModuloConexao;
import java.awt.Color;
import javax.swing.JOptionPane;

public class TelaLogin extends javax.swing.JFrame {

    Connection conexao = null;
    PreparedStatement pst = null;
    ResultSet rs = null;

    public void logar() {
        String sql = "select * from tbusuarios where login=? and senha=?";
        try {
            //as linhas abaixo preparam a consulta ao banco em função do
            //que foi digitado nas caixas de texto. O ? é substituido pel
            //conteúdo das variáveis
            pst = conexao.prepareStatement(sql);
            pst.setString(1, txtUsuario.getText());
            pst.setString(2, txtSenha.getText());

            rs = pst.executeQuery();

            if (rs.next()) {               
                String perfil = rs.getString(6);               

                if (perfil.equals("admin")) {
                    TelaPrincipal principal = new TelaPrincipal();
                    principal.setVisible(true);
                    TelaPrincipal.menRel.setEnabled(true);
                    TelaPrincipal.menCadUsu.setEnabled(true);
                    TelaPrincipal.lblUsuario.setText(rs.getString(2));
                    TelaPrincipal.lblUsuario.setForeground(Color.red);
                    this.dispose();
                } else {
                    TelaPrincipal principal = new TelaPrincipal();
                    principal.setVisible(true);                    
                    TelaPrincipal.lblUsuario.setText(rs.getString(2));
                    this.dispose();
                }


                conexao.close();
            } else {
                JOptionPane.showMessageDialog(null, "Usuário e/ou senha inválido(s)");
            }
        } catch (Exception e) {
            JOptionPane.showMessageDialog(null, e);
        }
    }

    public TelaLogin() {
        initComponents();
        conexao = ModuloConexao.conector();       

        if (conexao != null) {
            lblStatus.setIcon(new javax.swing.ImageIcon(getClass().getResource("/br/com/infox/icones/dbok.png")));
        } else {
            lblStatus.setIcon(new javax.swing.ImageIcon(getClass().getResource("/br/com/infox/icones/dberro.png")));
        }
    }

    /**
     * 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")

    private void initComponents() {

        jButton2 = new javax.swing.JButton();
        jLabel1 = new javax.swing.JLabel();
        jLabel2 = new javax.swing.JLabel();
        txtUsuario = new javax.swing.JTextField();
        btnLogin = new javax.swing.JButton();
        txtSenha = new javax.swing.JPasswordField();
        lblStatus = new javax.swing.JLabel();

        jButton2.setText("jButton2");

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
        setTitle("X System - Login");
        setResizable(false);

        jLabel1.setText("          Usuário");

        jLabel2.setText("  Senha");

        btnLogin.setText("Login");
        btnLogin.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                btnLoginActionPerformed(evt);
            }
        });

        lblStatus.setIcon(new javax.swing.ImageIcon(getClass().getResource("/br/com/infox/icones/dbok.png"))); // NOI18N

        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.TRAILING, false)
                    .addGroup(javax.swing.GroupLayout.Alignment.LEADING, layout.createSequentialGroup()
                        .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                            .addGroup(layout.createSequentialGroup()
                                .addGap(65, 65, 65)
                                .addComponent(jLabel1, javax.swing.GroupLayout.PREFERRED_SIZE, 76, javax.swing.GroupLayout.PREFERRED_SIZE))
                            .addGroup(javax.swing.GroupLayout.Alignment.TRAILING, layout.createSequentialGroup()
                                .addContainerGap()
                                .addComponent(jLabel2, javax.swing.GroupLayout.PREFERRED_SIZE, 45, javax.swing.GroupLayout.PREFERRED_SIZE)))
                        .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.UNRELATED)
                        .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.TRAILING, false)
                            .addComponent(txtSenha, javax.swing.GroupLayout.DEFAULT_SIZE, 328, Short.MAX_VALUE)
                            .addComponent(txtUsuario)))
                    .addGroup(layout.createSequentialGroup()
                        .addContainerGap(javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                        .addComponent(btnLogin))
                    .addGroup(javax.swing.GroupLayout.Alignment.LEADING, layout.createSequentialGroup()
                        .addGap(96, 96, 96)
                        .addComponent(lblStatus)))
                .addContainerGap())
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addGap(37, 37, 37)
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                    .addComponent(txtUsuario, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                    .addComponent(jLabel1, javax.swing.GroupLayout.PREFERRED_SIZE, 21, javax.swing.GroupLayout.PREFERRED_SIZE))
                .addGap(18, 18, 18)
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                    .addComponent(txtSenha, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                    .addComponent(jLabel2, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE))
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                    .addGroup(layout.createSequentialGroup()
                        .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
                        .addComponent(btnLogin))
                    .addGroup(layout.createSequentialGroup()
                        .addGap(21, 21, 21)
                        .addComponent(lblStatus)))
                .addGap(42, 42, 42))
        );

        setSize(new java.awt.Dimension(599, 262));
        setLocationRelativeTo(null);
    }// </editor-fold>                        

    private void btnLoginActionPerformed(java.awt.event.ActionEvent evt) {                                         
        //chamando o método logar
        logar();
    }                                        

    /**
     * @param args the command line arguments
     */
    public static void main(String args[]) {
        /* Set the Nimbus look and feel */
        //<editor-fold defaultstate="collapsed" desc=" Look and feel setting code (optional) ">
        /* If Nimbus (introduced in Java SE 6) is not available, stay with the default look and feel.
         * For details see http://download.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html 
         */
        try {
            for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) {
                if ("Nimbus".equals(info.getName())) {
                    javax.swing.UIManager.setLookAndFeel(info.getClassName());
                    break;
                }
            }
        } catch (ClassNotFoundException ex) {
            java.util.logging.Logger.getLogger(TelaLogin.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (InstantiationException ex) {
            java.util.logging.Logger.getLogger(TelaLogin.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (IllegalAccessException ex) {
            java.util.logging.Logger.getLogger(TelaLogin.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (javax.swing.UnsupportedLookAndFeelException ex) {
            java.util.logging.Logger.getLogger(TelaLogin.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        }
        //</editor-fold>

        /* Create and display the form */
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new TelaLogin().setVisible(true);
            }
        });
    }

    // Variables declaration - do not modify                     
    private javax.swing.JButton btnLogin;
    private javax.swing.JButton jButton2;
    private javax.swing.JLabel jLabel1;
    private javax.swing.JLabel jLabel2;
    private javax.swing.JLabel lblStatus;
    private javax.swing.JPasswordField txtSenha;
    private javax.swing.JTextField txtUsuario;
    // End of variables declaration                   
}

package br.com.infox.telas;

import java.text.DateFormat;
import java.util.Date;
import javax.swing.JOptionPane;


public class TelaPrincipal extends javax.swing.JFrame {

    public TelaPrincipal() {
        initComponents();    }


    private void initComponents() {

        desktop = new javax.swing.JDesktopPane();
        lblUsuario = new javax.swing.JLabel();
        lblData = new javax.swing.JLabel();
        jLabel1 = new javax.swing.JLabel();
        lblLogo = new javax.swing.JLabel();
        Menu = new javax.swing.JMenuBar();
        menCad = new javax.swing.JMenu();
        menCadCli = new javax.swing.JMenuItem();
        menCadOs = new javax.swing.JMenuItem();
        menCadUsu = new javax.swing.JMenuItem();
        menRel = new javax.swing.JMenu();
        menRelServ = new javax.swing.JMenuItem();
        MenAju = new javax.swing.JMenu();
        menAjuSob = new javax.swing.JMenuItem();
        menOpc = new javax.swing.JMenu();
        menOpcSair = new javax.swing.JMenuItem();

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
        setTitle("X - Sistema de Controle de Ordem de Serviço");
        setResizable(false);
        addWindowListener(new java.awt.event.WindowAdapter() {
            public void windowActivated(java.awt.event.WindowEvent evt) {
                formWindowActivated(evt);
            }
        });

        desktop.setPreferredSize(new java.awt.Dimension(630, 470));

        javax.swing.GroupLayout desktopLayout = new javax.swing.GroupLayout(desktop);
        desktop.setLayout(desktopLayout);
        desktopLayout.setHorizontalGroup(
            desktopLayout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGap(0, 630, Short.MAX_VALUE)
        );
        desktopLayout.setVerticalGroup(
            desktopLayout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGap(0, 470, Short.MAX_VALUE)
        );

        lblUsuario.setFont(new java.awt.Font("Tahoma", 1, 18)); // NOI18N
        lblUsuario.setText("Usuário");

        lblData.setFont(new java.awt.Font("Tahoma", 1, 24)); // NOI18N
        lblData.setText("Data");

        jLabel1.setIcon(new javax.swing.ImageIcon(getClass().getResource("/br/com/infox/icones/systemLogo (2).png"))); // NOI18N

        lblLogo.setIcon(new javax.swing.ImageIcon(getClass().getResource("/br/com/infox/icones/systemLogo.png"))); // NOI18N

        menCad.setText("Cadastro");

        menCadCli.setAccelerator(javax.swing.KeyStroke.getKeyStroke(java.awt.event.KeyEvent.VK_C, java.awt.event.InputEvent.ALT_MASK | java.awt.event.InputEvent.SHIFT_MASK));
        menCadCli.setText("Cliente");
        menCad.add(menCadCli);

        menCadOs.setAccelerator(javax.swing.KeyStroke.getKeyStroke(java.awt.event.KeyEvent.VK_O, java.awt.event.InputEvent.ALT_MASK | java.awt.event.InputEvent.SHIFT_MASK));
        menCadOs.setText("Ordem de Serviço");
        menCad.add(menCadOs);

        menCadUsu.setAccelerator(javax.swing.KeyStroke.getKeyStroke(java.awt.event.KeyEvent.VK_U, java.awt.event.InputEvent.ALT_MASK | java.awt.event.InputEvent.SHIFT_MASK));
        menCadUsu.setText("Usuário");
        menCadUsu.setEnabled(false);
        menCadUsu.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                menCadUsuActionPerformed(evt);
            }
        });
        menCad.add(menCadUsu);

        Menu.add(menCad);

        menRel.setText("Relatório");
        menRel.setEnabled(false);

        menRelServ.setAccelerator(javax.swing.KeyStroke.getKeyStroke(java.awt.event.KeyEvent.VK_S, java.awt.event.InputEvent.ALT_MASK));
        menRelServ.setText("Serviços");
        menRel.add(menRelServ);

        Menu.add(menRel);

        MenAju.setText("Ajuda");

        menAjuSob.setAccelerator(javax.swing.KeyStroke.getKeyStroke(java.awt.event.KeyEvent.VK_F1, java.awt.event.InputEvent.ALT_MASK));
        menAjuSob.setText("Sobre");
        menAjuSob.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                menAjuSobActionPerformed(evt);
            }
        });
        MenAju.add(menAjuSob);

        Menu.add(MenAju);

        menOpc.setText("Opções");

        menOpcSair.setAccelerator(javax.swing.KeyStroke.getKeyStroke(java.awt.event.KeyEvent.VK_F4, java.awt.event.InputEvent.ALT_MASK));
        menOpcSair.setText("Sair");
        menOpcSair.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                menOpcSairActionPerformed(evt);
            }
        });
        menOpc.add(menOpcSair);

        Menu.add(menOpc);

        setJMenuBar(Menu);

        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addComponent(desktop, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addGap(62, 62, 62)
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                    .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.TRAILING)
                        .addComponent(lblUsuario)
                        .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                            .addComponent(jLabel1)
                            .addComponent(lblData)))
                    .addComponent(lblLogo))
                .addContainerGap(61, Short.MAX_VALUE))
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(javax.swing.GroupLayout.Alignment.TRAILING, layout.createSequentialGroup()
                .addGap(83, 83, 83)
                .addComponent(lblUsuario)
                .addGap(55, 55, 55)
                .addComponent(lblData)
                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                .addComponent(jLabel1)
                .addGap(55, 55, 55)
                .addComponent(lblLogo)
                .addGap(87, 87, 87))
            .addGroup(layout.createSequentialGroup()
                .addComponent(desktop, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addGap(0, 0, Short.MAX_VALUE))
        );

        setSize(new java.awt.Dimension(869, 523));
        setLocationRelativeTo(null);
    }// </editor-fold>                        

    private void menCadUsuActionPerformed(java.awt.event.ActionEvent evt) {                                          
        // as linhas abaixo abrir o form TelaUsuario dentro do desktop pane
        TelaUsuario usuario = new TelaUsuario();
        usuario.setVisible(true);
        desktop.add(usuario);
    }                                         

    private void formWindowActivated(java.awt.event.WindowEvent evt) {                                     
        // as linhas abaixo subsituem a label Data lblData, pela data atual do sistema ao inicializar o form.
        Date data = new Date();
        DateFormat formatador = DateFormat.getDateInstance(DateFormat.SHORT);
        lblData.setText(formatador.format(data));
    }                                    

    private void menOpcSairActionPerformed(java.awt.event.ActionEvent evt) {                                           
        // exibe uma caixa de diálogo antes de sair do sistema
        int sair = JOptionPane.showConfirmDialog(null,"Tem certeza que deseja sair?","Atenção",JOptionPane.YES_NO_OPTION);
        if (sair == JOptionPane.YES_OPTION) {
            System.exit(0);
        }
    }                                          

    private void menAjuSobActionPerformed(java.awt.event.ActionEvent evt) {                                          
        //chamando a tela sobre
        TelaSobre sobre = new TelaSobre();
        sobre.setVisible(true);

    }                                         


    public static void main(String args[]) {     

        try {
            for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) {
                if ("Nimbus".equals(info.getName())) {
                    javax.swing.UIManager.setLookAndFeel(info.getClassName());
                    break;
                }
            }
        } catch (ClassNotFoundException ex) {
            java.util.logging.Logger.getLogger(TelaPrincipal.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (InstantiationException ex) {
            java.util.logging.Logger.getLogger(TelaPrincipal.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (IllegalAccessException ex) {
            java.util.logging.Logger.getLogger(TelaPrincipal.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (javax.swing.UnsupportedLookAndFeelException ex) {
            java.util.logging.Logger.getLogger(TelaPrincipal.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        }
        //</editor-fold>

        /* Create and display the form */
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new TelaPrincipal().setVisible(true);
            }
        });
    }

    // Variables declaration - do not modify                     
    private javax.swing.JMenu MenAju;
    private javax.swing.JMenuBar Menu;
    private javax.swing.JDesktopPane desktop;
    private javax.swing.JLabel jLabel1;
    private javax.swing.JLabel lblData;
    private javax.swing.JLabel lblLogo;
    public static javax.swing.JLabel lblUsuario;
    private javax.swing.JMenuItem menAjuSob;
    private javax.swing.JMenu menCad;
    private javax.swing.JMenuItem menCadCli;
    private javax.swing.JMenuItem menCadOs;
    public static javax.swing.JMenuItem menCadUsu;
    private javax.swing.JMenu menOpc;
    private javax.swing.JMenuItem menOpcSair;
    public static javax.swing.JMenu menRel;
    private javax.swing.JMenuItem menRelServ;
    // End of variables declaration                   
}

package br.com.infox.telas;

public class TelaSobre extends javax.swing.JFrame {


    public TelaSobre() {
        initComponents();
    }


    @SuppressWarnings("unchecked")
    // <editor-fold defaultstate="collapsed" desc="Generated Code">                          
    private void initComponents() {

        jLabel1 = new javax.swing.JLabel();
        jLabel2 = new javax.swing.JLabel();
        jLabel3 = new javax.swing.JLabel();
        jLabel4 = new javax.swing.JLabel();

        setDefaultCloseOperation(javax.swing.WindowConstants.DISPOSE_ON_CLOSE);
        addWindowListener(new java.awt.event.WindowAdapter() {
            public void windowActivated(java.awt.event.WindowEvent evt) {
                formWindowActivated(evt);
            }
        });

        jLabel1.setFont(new java.awt.Font("Tahoma", 1, 12)); // NOI18N
        jLabel1.setText("Sistema para Controle de Ordem de Serviços");

        jLabel2.setFont(new java.awt.Font("Tahoma", 1, 11)); // NOI18N
        jLabel2.setText("Desenvolvido por: Carlos Eduardo ");

        jLabel3.setFont(new java.awt.Font("Tahoma", 1, 11)); // NOI18N
        jLabel3.setText("Sob a licença GPL");

        jLabel4.setIcon(new javax.swing.ImageIcon(getClass().getResource("/br/com/infox/icones/about.png"))); // NOI18N

        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                    .addGroup(layout.createSequentialGroup()
                        .addGap(49, 49, 49)
                        .addComponent(jLabel1))
                    .addGroup(layout.createSequentialGroup()
                        .addGap(92, 92, 92)
                        .addComponent(jLabel2))
                    .addGroup(layout.createSequentialGroup()
                        .addGap(136, 136, 136)
                        .addComponent(jLabel3))
                    .addGroup(layout.createSequentialGroup()
                        .addGap(152, 152, 152)
                        .addComponent(jLabel4)))
                .addContainerGap())
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addGap(40, 40, 40)
                .addComponent(jLabel1)
                .addGap(13, 13, 13)
                .addComponent(jLabel2)
                .addGap(18, 18, 18)
                .addComponent(jLabel3)
                .addGap(18, 18, 18)
                .addComponent(jLabel4)
                .addContainerGap(53, Short.MAX_VALUE))
        );

        setSize(new java.awt.Dimension(392, 294));
        setLocationRelativeTo(null);
    }// </editor-fold>                        

    private void formWindowActivated(java.awt.event.WindowEvent evt) {                                     
        // TODO add your handling code here:
    }                                    

    /**
     * @param args the command line arguments
     */
    public static void main(String args[]) {
        /* Set the Nimbus look and feel */
        //<editor-fold defaultstate="collapsed" desc=" Look and feel setting code (optional) ">
        /* If Nimbus (introduced in Java SE 6) is not available, stay with the default look and feel.
         * For details see http://download.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html 
         */
        try {
            for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) {
                if ("Nimbus".equals(info.getName())) {
                    javax.swing.UIManager.setLookAndFeel(info.getClassName());
                    break;
                }
            }
        } catch (ClassNotFoundException ex) {
            java.util.logging.Logger.getLogger(TelaSobre.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (InstantiationException ex) {
            java.util.logging.Logger.getLogger(TelaSobre.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (IllegalAccessException ex) {
            java.util.logging.Logger.getLogger(TelaSobre.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (javax.swing.UnsupportedLookAndFeelException ex) {
            java.util.logging.Logger.getLogger(TelaSobre.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        }
        //</editor-fold>

        /* Create and display the form */
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new TelaSobre().setVisible(true);
            }
        });
    }

    // Variables declaration - do not modify                     
    private javax.swing.JLabel jLabel1;
    private javax.swing.JLabel jLabel2;
    private javax.swing.JLabel jLabel3;
    private javax.swing.JLabel jLabel4;
    // End of variables declaration                   
}

package br.com.infox.dal;

import java.sql.*;


public class ModuloConexao {
    //método responsável por estabelecer a conexão com o banco
    public static Connection conector() {
        java.sql.Connection conexao = null;
     // a linha abaixo chama  o driver que importei para a biblioteca
     String driver = "com.mysql.jdbc.Driver";
     // armazenando informações referente ao banco
     String url="jdbc:mysql://localhost:3306/dbinfox";
     String user="root";
     String password ="";
     //estabelecendo a conexão com o banco

        try {
            Class.forName(driver);
            conexao = DriverManager.getConnection(url, user, password);
            return conexao;

        } catch (Exception e) {
            //a linha abaixo serve de apoio para esclarecer o erro
            //System.out.println(e);
            return null;
        }

    }
}
java mysql swing jdbc nullpointerexception

  • Hello Eduardo, welcome to stackoverflow. From the experience I have with Java and IT in general, the way you are describing the problem, it would be very difficult to find it, you have already learned to use the mode debug of your IDE?

1 answer

1

Look at this:

    } catch (Exception e) {
        //a linha abaixo serve de apoio para esclarecer o erro
        //System.out.println(e);
        return null;
    }

That one return null; is a very, very, very bad idea! In addition to causing any code that tries to connect in the database, if it finds an error, it results in a NullPointerException, on top of which it hides and swallows the real cause of the error. The solution is to simply leave the SQLException be launched, after all, it was invented for that and is there for a good reason. Trying to bury or hide the mistake is not a good idea.

Let’s rewrite the code of this last class of yours, considering that old answer of mine for that:

package br.com.infox.dal;

import java.sql.*;

public class ModuloConexao {

    static {
        try {
            Class.forName("com.mysql.jdbc.Driver");
        } catch (ClassNotFoundException e) {
            throw new ExceptionInInitializerError(e);
        }
    }

    private static final String URL = "jdbc:mysql://localhost:3306/dbinfox";
    private static final String USER = "root";
    private static final String PASSWORD = "";

    //método responsável por estabelecer a conexão com o banco
    public static Connection conector() throws SQLException {
        return DriverManager.getConnection(URL, USER, PASSWORD);
    }
}

Let’s see your method logar:

Connection conexao = null;
PreparedStatement pst = null;
ResultSet rs = null;

public void logar() {
    String sql = "select * from tbusuarios where login=? and senha=?";
    try {
        //as linhas abaixo preparam a consulta ao banco em função do
        //que foi digitado nas caixas de texto. O ? é substituido pel
        //conteúdo das variáveis
        pst = conexao.prepareStatement(sql);
        pst.setString(1, txtUsuario.getText());
        pst.setString(2, txtSenha.getText());

        rs = pst.executeQuery();

        if (rs.next()) {               
            String perfil = rs.getString(6);               

            if (perfil.equals("admin")) {
                TelaPrincipal principal = new TelaPrincipal();
                principal.setVisible(true);
                TelaPrincipal.menRel.setEnabled(true);
                TelaPrincipal.menCadUsu.setEnabled(true);
                TelaPrincipal.lblUsuario.setText(rs.getString(2));
                TelaPrincipal.lblUsuario.setForeground(Color.red);
                this.dispose();
            } else {
                TelaPrincipal principal = new TelaPrincipal();
                principal.setVisible(true);                    
                TelaPrincipal.lblUsuario.setText(rs.getString(2));
                this.dispose();
            }


            conexao.close();
        } else {
            JOptionPane.showMessageDialog(null, "Usuário e/ou senha inválido(s)");
        }
    } catch (Exception e) {
        JOptionPane.showMessageDialog(null, e);
    }
}

Well, here are several problems:

  • Use the Try-with-Resources adequately. See more in this question here.

  • Don’t put the Connection, PreparedStatement and ResultSet as instance variables. They are expensive and ephemeral resources that must be closed and discarded after use. By placing them as instance variables, it is very difficult to control their lifespan properly.

  • There’s repeated code inside the if and of else. When this happens, almost always you can move the code out of the if.

  • You saw that you initialize the variable conexao with null and in the method logar() you make a conexao.prepareStatement(sql)? Yeah, that’ll get you a nice NullPointerException.

  • Ah, but there’s that conexao = ModuloConexao.conector(); and with it the conexao would not give NullPointerException. It occurs that if the conector() swallow and hide the error, it will yes. Well, remove that line, because the connection is ephemeral (as already explained) and should be treated with the Try-with-Resources. Unless you know very well what you are doing (it is not what the code demonstrates), it is best to connect, use the connection, and as soon as possible, close it and discard it.

To rewrite this method, let’s start with TelaPrincipal. Let’s start with this code:

            if (perfil.equals("admin")) {
                TelaPrincipal principal = new TelaPrincipal();
                principal.setVisible(true);
                TelaPrincipal.menRel.setEnabled(true);
                TelaPrincipal.menCadUsu.setEnabled(true);
                TelaPrincipal.lblUsuario.setText(rs.getString(2));
                TelaPrincipal.lblUsuario.setForeground(Color.red);
                this.dispose();
            } else {
                TelaPrincipal principal = new TelaPrincipal();
                principal.setVisible(true);                    
                TelaPrincipal.lblUsuario.setText(rs.getString(2));
                this.dispose();
            }

This can be simplified for this:

            TelaPrincipal principal = new TelaPrincipal();
            principal.setVisible(true);
            TelaPrincipal.lblUsuario.setText(rs.getString(2));
            if (perfil.equals("admin")) {
                TelaPrincipal.menRel.setEnabled(true);
                TelaPrincipal.menCadUsu.setEnabled(true);
                TelaPrincipal.lblUsuario.setForeground(Color.red);
            }
            this.dispose();

But this is still not very good. Note these instructions:

TelaPrincipal.lblUsuario.setText(rs.getString(2));
TelaPrincipal.menRel.setEnabled(true);
TelaPrincipal.menCadUsu.setEnabled(true);
TelaPrincipal.lblUsuario.setForeground(Color.red);

They show that you are misusing the static within the class TelaPrincipal:

public static javax.swing.JLabel lblUsuario;
public static javax.swing.JMenuItem menCadUsu;
public static javax.swing.JMenu menRel;

They should all be private and without static. Public attributes are almost always a bad idea, even worse when static. The exceptions to this are only a few cases of constants and immutable objects or singletons. This way it is, this is a violation of encapsulation. I speak more of this here (along with a lot of other things).

To fix this, after all return to private and without static, create this constructor of TelaPrincipal, incorporating part of the code that was in logar():

public TelaPrincipal(boolean admin, String nome) {
    initComponents();
    if (admin) {
        this.menRel.setEnabled(true);
        this.menCadUsu.setEnabled(true);
        this.lblUsuario.setForeground(Color.red);
    }
    this.lblUsuario.setText(nome);
    this.setVisible(true);
}

Then delete the old constructor:

public TelaPrincipal() {
    initComponents();    }

In class TelaPrincipal, also delete the method main. The only main what matters is that of TelaLogin.

Now, let’s rewrite the method logar():

public void logar() {
    String sql = "select * from tbusuarios where login=? and senha=?";
    String perfil = "", nome = "";

    try (
            Connection conexao = ModuloConexao.conectar();
            PreparedStatement pst = conexao.prepareStatement(sql);
    ) {
        pst.setString(1, txtUsuario.getText());
        pst.setString(2, txtSenha.getText());

        try (ResultSet rs = pst.executeQuery()) {
            if (!rs.next()) {
                JOptionPane.showMessageDialog(null, "Usuário e/ou senha inválido(s)");
                return;
            }
            perfil = rs.getString(6);
            nome = rs.getString(2);
        }
    } catch (Exception e) {
        JOptionPane.showMessageDialog(null, e);
        return;
    }

    new TelaPrincipal(perfil.equals("admin"), nome);
    this.dispose();
}

Other tips:

  • Do not use System.exit(0);. This is bad programming practice. It’s your application’s self-destruct button. When using this, you can’t save, you can’t close open files or anything. Instead, call the method dispose() of your JFrame. I’ve talked about it too ancient answer.

  • The classes Date and DateFormat have already died, but forgot to bury. Try not to use them ever again. Instead, use LocalDate or LocalDateTime in place of Date and DateTimeFormatter in place of DateFormat. See more of this here and/or here.

  • Do not mix in the same classes the presentation logic (which uses swing) with database logic (which uses JDBC). The reason is that you should not want your data access logic to be tied to the swing, nor should the system view rules be tied to database details. This separation is done by applying the MVC standard.

  • thank you so much for the very important comment Victor Stafusa! for beginners like me, this is an incredible stimulus!

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