import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.border.*;
import java.sql.*;
import java.util.*;

public class SQLClient extends JApplet {
  // Connection to the database
  private Connection connection;

  // Statement to execute SQL commands
  private Statement statement;

  // Text area to enter SQL commands
  private JTextArea jtasqlCommand = new JTextArea();

  // Text area to display results from SQL commands
  private JTextArea jtaSQLResult = new JTextArea();

  // JDBC info for a database connection
  JTextField jtfUsername = new JTextField();
  JPasswordField jpfPassword = new JPasswordField();
  JComboBox jcboURL = new JComboBox(new String[] {
    "jdbc:mysql://liang.armstrong.edu/javabook",
    "jdbc:odbc:exampleMDBDataSource",
    "jdbc:oracle:thin:@liang.armstrong.edu:1521:orcl"});
  JComboBox jcboDriver = new JComboBox(new String[] {
    "com.mysql.jdbc.Driver", "sun.jdbc.odbc.JdbcOdbcDriver",
    "oracle.jdbc.driver.OracleDriver"});

  JButton jbtExecuteSQL = new JButton("Execute SQL Command");
  JButton jbtClearSQLCommand = new JButton("Clear");
  JButton jbtConnectDB1 = new JButton("Connect to Database");
  JButton jbtClearSQLResult = new JButton("Clear Result");

  // Create titled borders
  Border titledBorder1 = new TitledBorder("Enter an SQL Command");
  Border titledBorder2 = new TitledBorder("SQL Execution Result");
  Border titledBorder3 = new TitledBorder(
    "Enter Database Information");

  JLabel jlblConnectionStatus = new JLabel("No connection now");

  /** Initialize the applet */
  public void init() {
    JScrollPane jScrollPane1 = new JScrollPane(jtasqlCommand);
    jScrollPane1.setBorder(titledBorder1);
    JScrollPane jScrollPane2 = new JScrollPane(jtaSQLResult);
    jScrollPane2.setBorder(titledBorder2);

    JPanel jPanel1 = new JPanel(new FlowLayout(FlowLayout.RIGHT));
    jPanel1.add(jbtClearSQLCommand);
    jPanel1.add(jbtExecuteSQL);

    JPanel jPanel2 = new JPanel();
    jPanel2.setLayout(new BorderLayout());
    jPanel2.add(jScrollPane1, BorderLayout.CENTER);
    jPanel2.add(jPanel1, BorderLayout.SOUTH);
    jPanel2.setPreferredSize(new Dimension(100, 100));

    JPanel jPanel3 = new JPanel();
    jPanel3.setLayout(new BorderLayout());
    jPanel3.add(jlblConnectionStatus, BorderLayout.CENTER);
    jPanel3.add(jbtConnectDB1, BorderLayout.EAST);

    JPanel jPanel4 = new JPanel();
    jPanel4.setLayout(new GridLayout(4, 1, 10, 5));
    jPanel4.add(jcboDriver);
    jPanel4.add(jcboURL);
    jPanel4.add(jtfUsername);
    jPanel4.add(jpfPassword);

    JPanel jPanel5 = new JPanel();
    jPanel5.setLayout(new GridLayout(4, 1));
    jPanel5.add(new JLabel("JDBC Driver"));
    jPanel5.add(new JLabel("Database URL"));
    jPanel5.add(new JLabel("Username"));
    jPanel5.add(new JLabel("Password"));

    JPanel jPanel6 = new JPanel();
    jPanel6.setLayout(new BorderLayout());
    jPanel6.setBorder(titledBorder3);
    jPanel6.add(jPanel4, BorderLayout.CENTER);
    jPanel6.add(jPanel5, BorderLayout.WEST);

    JPanel jPanel7 = new JPanel();
    jPanel7.setLayout(new BorderLayout());
    jPanel7.add(jPanel3, BorderLayout.SOUTH);
    jPanel7.add(jPanel6, BorderLayout.CENTER);

    JPanel jPanel8 = new JPanel();
    jPanel8.setLayout(new BorderLayout());
    jPanel8.add(jPanel2, BorderLayout.CENTER);
    jPanel8.add(jPanel7, BorderLayout.WEST);

    JPanel jPanel9 = new JPanel(new FlowLayout(FlowLayout.LEFT));
    jPanel9.add(jbtClearSQLResult);

    jcboURL.setEditable(true);
    jcboDriver.setEditable(true);

    add(jPanel8, BorderLayout.NORTH);
    add(jScrollPane2, BorderLayout.CENTER);
    add(jPanel9, BorderLayout.SOUTH);

    jbtExecuteSQL.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) {
          executeSQL();
       }
    });
    jbtConnectDB1.addActionListener(new ActionListener() {
      public void actionPerformed(ActionEvent e) {
        connectToDB();
      }
    });
    jbtClearSQLCommand.addActionListener(new ActionListener() {
      public void actionPerformed(ActionEvent e) {
        jtasqlCommand.setText(null);
      }
    });
    jbtClearSQLResult.addActionListener(new ActionListener() {
      public void actionPerformed(ActionEvent e) {
        jtaSQLResult.setText(null);
      }
    });
  }

  /** Connect to DB */
  private void connectToDB() {
    // Get database information from the user input
    String driver = (String)jcboDriver.getSelectedItem();
    String url = (String)jcboURL.getSelectedItem();
    String username = jtfUsername.getText().trim();
    String password = new String(jpfPassword.getPassword());

    // Connection to the database
    try {
      Class.forName(driver);
      connection = DriverManager.getConnection(
        url, username, password);
      jlblConnectionStatus.setText("Connected to " + url);
    }
    catch (java.lang.Exception ex) {
      ex.printStackTrace();
    }
  }

  /** Execute SQL commands */
  private void executeSQL() {
    if (connection == null) {
      jtaSQLResult.setText("Please connect to a database first");
      return;
    }
    else {
      String sqlCommands = jtasqlCommand.getText().trim();
      String[] commands = sqlCommands.replace('\n', ' ').split(";");

      for (String aCommand: commands) {
        if (aCommand.trim().toUpperCase().startsWith("SELECT")) {
          processSQLSelect(aCommand);
        }
        else {
          processSQLNonSelect(aCommand);
        }
      }
    }
  }

  /** Execute SQL SELECT commands */
  private void processSQLSelect(String sqlCommand) {
    try {
      // Get a new statement for the current connection
      statement = connection.createStatement();

      // Execute a SELECT SQL command
      ResultSet resultSet = statement.executeQuery(sqlCommand);

      // Find the number of columns in the result set
      int columnCount = resultSet.getMetaData().getColumnCount();
      String row = "";

      // Display column names
      for (int i = 1; i <= columnCount; i++) {
        row += resultSet.getMetaData().getColumnName(i) + "\t";
      }

      jtaSQLResult.append(row + '\n');

      while (resultSet.next()) {
        // Reset row to empty
        row = "";

        for (int i = 1; i <= columnCount; i++) {
          // A non-String column is converted to a string
          row += resultSet.getString(i) + "\t";
        }

        jtaSQLResult.append(row + '\n');
      }
    }
    catch (SQLException ex) {
      jtaSQLResult.setText(ex.toString());
    }
  }

  /** Execute SQL DDL, and modification commands */
  private void processSQLNonSelect(String sqlCommand) {
    try {
      // Get a new statement for the current connection
      statement = connection.createStatement();

      // Execute a non-SELECT SQL command
      statement.executeUpdate(sqlCommand);

      jtaSQLResult.setText("SQL command executed");
    }
    catch (SQLException ex) {
      jtaSQLResult.setText(ex.toString());
    }
  }

  /** Main method */
  public static void main(String[] args) {
    SQLClient applet = new SQLClient();
    JFrame frame = new JFrame();
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setTitle("Interactive SQL Client");
    frame.getContentPane().add(applet, BorderLayout.CENTER);
    applet.init();
    applet.start();
    frame.setSize(700, 320);
    Dimension d = Toolkit.getDefaultToolkit().getScreenSize();
    frame.setLocation((d.width - frame.getSize().width) / 2,
      (d.height - frame.getSize().height) / 2);
    frame.setVisible(true);
  }
}