Um simples login gráfico com swing em java. Checa a senha com um banco de dados mysql.

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/* Simples login, por Diogo Souza da Silva */
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.sql.*;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;

public class Login extends JFrame{
   /* Declarando variaveis */
    static Login janela ;
    public JTextField usuario ;
    public JPasswordField password ;
    public String userid, erro, asenha ;
    
   public Login() {
      /* Constroi a tela de LOGIN com gridBaglayout */
      Container contantPane = getContentPane();
      GridBagLayout gridbag = new GridBagLayout();
      GridBagConstraints c = new GridBagConstraints();
      contantPane.setLayout(gridbag);
      
      getContentPane().setBackground(Color.white);
      
      JLabel intro = new JLabel("Bem vindo ao JContas! - www.manifesto.s9k.net");
       c.gridwidth = 2;
       c.weightx = 0.5;
       c.gridx = 0;
       c.gridy = 0;
       gridbag.setConstraints(intro, c);
       getContentPane().add(intro);
       
       JLabel user = new JLabel("Usuario:");
       c.gridwidth = 1;
       c.gridx = 0;
       c.gridy = 2;
       gridbag.setConstraints(user, c);
       getContentPane().add(user);
       
       JLabel senha = new JLabel("Senha:");
       c.gridwidth = 1;
       c.gridx = 0;
       c.gridy = 3;
       gridbag.setConstraints(senha, c);
       getContentPane().add(senha);
      
       usuario = new JTextField(15);
       c.gridwidth = 1;
       c.gridx = 1;
       c.gridy = 2;
       gridbag.setConstraints(usuario, c);
       getContentPane().add(usuario);
       
       password = new JPasswordField(15);
       c.gridwidth = 1;
       c.gridx = 1;
       c.gridy = 3;
       gridbag.setConstraints(password, c);
       getContentPane().add(password);
       
       JButton entra = new JButton("Entrar");
       c.gridwidth = 1;
       c.gridx = 0;
       c.gridy = 4;
       gridbag.setConstraints(entra, c);
       getContentPane().add(entra);
       /* Funcao de entrar  */
       entra.addActionListener( new ActionListener()
       
         {
      public void actionPerformed(ActionEvent e) {
         validar();
   }});
}
   
   public void validar() {
      /* Confere usuario e senha com um mysql */
         Connection con;
         Statement stmt;
         ResultSet rs;
      
         String usu = new String(usuario.getText());
         String senhas = new String(password.getPassword());
         /* Pega a senha de um mysql */
         try {
         Class.forName("com.mysql.jdbc.Driver");
         System.out.println("Driver OK");
                try {
            String url = "jdbc:mysql://localhost/data_base";
            con = DriverManager.getConnection(url, "root", "");
            stmt = con.createStatement();
                  try {
                     rs = stmt.executeQuery("SELECT senha FROM usuarios where login = '"+ usu +"' ");
                     rs.next();
                     asenha = rs.getString("senha");
                        } catch (SQLException exp) {
                           erro = erro+"Erro na requisicao.";
                           System.out.println("SQLException: " + exp.getMessage());
                           System.out.println("SQLState: " + exp.getSQLState());
                           System.out.println("VendorError: " + exp.getErrorCode());
                           exp.printStackTrace();
                        }
               } catch (SQLException exp) {
               erro = erro+"Conexao falha, verifique sua conexao com a internet.";
               System.out.println("SQLException: " + exp.getMessage());
               System.out.println("SQLState: " + exp.getSQLState());
               System.out.println("VendorError: " + exp.getErrorCode());
               exp.printStackTrace();
               }
         } catch(java.lang.ClassNotFoundException ext) {
            erro = "Problemas com o driver de conexao.";
            System.err.print("ClassNotFoundException: "); 
            System.err.println(ext.getMessage());
         }

         /* Se devidamente autorizado */
          if ( senhas.equals(asenha) )
          {
               /*  Faz o que precisar */
          }
          else {
              JOptionPane.showMessageDialog(null,"Acesso negado."+erro,"Atencao", JOptionPane.WARNING_MESSAGE);
                    }
   }
     
   public static void main(String[] args) {
      /* Chama o programa */
      janela = new Login() ;
      janela.setTitle("Login");
      janela.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      janela.pack();
      janela.setVisible(true);   
   }   
}

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