In this chapter:

• Java 2 and CORBA
• Creating a CORBA interface
• Creating a CORBA server
• Creating a CORBA client

A detailed description of both CORBA and the CORBA-related Java 2 packages lies far beyond the scope of this book. However, we feel that the potential for this technology is strong enough to warrant the inclusion of an example application showing how to implement a CORBA-enabled back end with Swing up front. For readers completely new to CORBA, we suggest referencing the following URL before moving on: http://www.omg.org/corba/beginners.html.

The example in this chapter is presented in three parts and demonstrates how we can build a complete CORBA-enabled Java application using Swing as a front end, CORBA as middleware, and a database server as a backend. We will build this application using our stocks table example presented in chapter 18 as a base, and we will use a CORBA-enabled remote server to supply stock data.

To start the construction of a CORBA-enabled application we first need to define an IDL interface which will be used to retrieve data from a remote server. The example in this section presents two such interfaces and two user-defined exceptions in one module IDL file.

module MarketDataApp
{
  interface DataUnit {
    string getSymbol();
    string getName();
    double getLast();
    double getOpen();
    double getChange();
    double getChangePr();
    long getVolume();
  };

  exception CorbaSqlException {
    string reason;
  };

  exception LoginException {
  };

  interface MarketData {
    DataUnit getFirstData(in string name, in string password, 
      in long year, in long month, in long day)
      raises(LoginException, CorbaSqlException);

    DataUnit getNextData()
      raises(CorbaSqlException);
  };
};

idltojava -fverbose -fno-cpp MarketData.idl

This command will generate a number of Java source files in a "MarketDataApp" sub-directory:

/*
 * File: ./MARKETDATAAPP/DATAUNIT.JAVA
 * From: MARKETDATA.IDL
 * Date: Tue Feb 09 11:31:12 1999
 *   By: idltojava Java IDL 1.2 Aug 18 1998 16:25:34
 */

package MarketDataApp;
public interface DataUnit extends org.omg.CORBA.Object,
 org.omg.CORBA.portable.IDLEntity 
{
  String getSymbol();
  String getName();
  double getLast();
  double getOpen();
  double getChange();
  double getChangePr();
  int getVolume();
}

package MarketDataApp;

import java.sql.*;

public class DataUnitImpl extends _DataUnitImplBase 
{
  protected String  m_symbol;
  protected String  m_name;
  protected double  m_last;
  protected double  m_open;
  protected double  m_change;
  protected double  m_changePr;
  protected long    m_volume;

  public DataUnitImpl(ResultSet results)
   throws SQLException {
    m_symbol = results.getString(1);
    m_name = results.getString(2);
    m_last = results.getDouble(3);
    m_open = results.getDouble(4);
    m_change = results.getDouble(5);
    m_changePr = results.getDouble(6);
    m_volume = results.getLong(7);
  }

  public String getSymbol()   { return m_symbol; }
  public String getName()     { return m_name; }
  public double getLast()     { return m_last; }
  public double getOpen()     { return m_open; }
  public double getChange()   { return m_change; }
  public double getChangePr() { return m_changePr; }
  public int getVolume()      { return (int)m_volume; }
}

/*
 * File: ./MARKETDATAAPP/MARKETDATA.JAVA
 * From: MARKETDATA.IDL
 * Date: Tue Feb 09 11:31:12 1999
 *   By: idltojava Java IDL 1.2 Aug 18 1998 16:25:34
 */

package MarketDataApp;

public interface MarketData extends org.omg.CORBA.Object, 
 org.omg.CORBA.portable.IDLEntity 
{
  MarketDataApp.DataUnit getFirstData(String name, 
   String password, int year, int month, int day)
    throws MarketDataApp.LoginException,
    MarketDataApp.CorbaSqlException;

  MarketDataApp.DataUnit getNextData()
   throws MarketDataApp.CorbaSqlException;
}

package MarketDataApp;

import java.sql.*;
import java.util.*;

import org.omg.CosNaming.*;
import org.omg.CosNaming.NamingContextPackage.*;
import org.omg.CORBA.*;

public class MarketDataServer extends _MarketDataImplBase
{
  protected Connection m_conn;
  protected Statement  m_stmt;
  protected ResultSet  m_results;

  public MarketDataServer() {
    try {
      // Load the JDBC-ODBC bridge driver
      Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
    }
    catch (Exception e) {
      e.printStackTrace();
    }
  }

  public DataUnit getFirstData(String name, String password, 
   int year, int month, int day)
   throws MarketDataApp.LoginException, MarketDataApp.CorbaSqlException
  {
    if (!name.equals("CORBA") || !password.equals("Swing"))
      throw new MarketDataApp.LoginException();

    String query = "SELECT data.symbol, symbols.name, "+
      "data.last, data.open, data.change, data.changeproc, "+
      "data.volume FROM DATA INNER JOIN SYMBOLS "+
      "ON DATA.symbol = SYMBOLS.symbol WHERE "+
      "month(data.date1)="+month+" AND day(data.date1)="+day+
      " AND year(data.date1)="+year;

    try {
      m_conn = DriverManager.getConnection(
        "jdbc:odbc:Market", "admin", "");

      m_stmt = m_conn.createStatement();
        m_results = m_stmt.executeQuery(query);

      if (m_results.next())
        return new DataUnitImpl(m_results);
      else {
        disconnect();
        return null;
      }
    }
    catch (Exception e) {
      e.printStackTrace();
      throw new CorbaSqlException(e.toString());
    }
  }

  public DataUnit getNextData() 
   throws MarketDataApp.CorbaSqlException {
    try {
      if (m_results != null && m_results.next())
        return new DataUnitImpl(m_results);
      else {
        disconnect();
        return null;
      }
    }
    catch (Exception e) {
      e.printStackTrace();
      throw new CorbaSqlException(e.toString());
    }
  }

  protected void disconnect() {
    try {
      if (m_results != null)
        m_results.close();
      if (m_stmt != null)
        m_stmt.close();
      if (m_conn != null)
        m_conn.close();
    }
    catch (Exception e) {
      e.printStackTrace();
    }
    m_results = null;
    m_stmt = null;
    m_conn = null;
  }

  public static void main(String args[]) {    
    try {
      // create and initialize the ORB 
      Properties props = new Properties();
      props.put("org.omg.CORBA.ORBInitialPort", "1250");
      ORB orb = ORB.init(args, props); 
            
      // create server and register it with the ORB
      MarketDataServer server = new MarketDataServer(); 
      orb.connect(server); 
            
      // get the root naming context 
      org.omg.CORBA.Object objRef = 
        orb.resolve_initial_references("NameService");
      NamingContext ncRef = NamingContextHelper.narrow(objRef); 

      // bind the Object Reference in Naming
      NameComponent nc = new NameComponent("MarketData", "");
      NameComponent path[] = {nc};        
      ncRef.rebind(path, server); 
            
      // wait for invocations from clients
      java.lang.Object sync = new java.lang.Object();
      synchronized (sync) { 
        System.out.println("Waiting for client connection");
        sync.wait(); 
      } 
    } 
    catch (Exception e) {
      e.printStackTrace();
    }
  }
}

Its finally time to take a look at how we can modify our stocks table application from chapter 18 to retrieve data from the CORBA server.

<<file figure26-1.gif>>

import java.awt.*;
import java.awt.event.*;
import java.util.*;
import java.io.*;
import java.text.*;

import javax.swing.*;
import javax.swing.border.*;
import javax.swing.event.*;
import javax.swing.table.*;

import dl.*;
import MarketDataApp.*;

import org.omg.CosNaming.*;
import org.omg.CosNaming.NamingContextPackage.*;
import org.omg.CORBA.*;

public class StocksTable extends JFrame 
{
  protected JTable m_table;
  protected StockTableData m_data;
  protected JLabel m_title;

  private String m_name = "CORBA";
  private String m_password = "Swing";
  protected MarketData m_server = null;    // Remote server ref.

  public StocksTable() {
    super("Swing Table [CORBA]");
    setSize(770, 300);
    getContentPane().setLayout(new BorderLayout());

    // Unchanged code
    WindowListener wndCloser = new WindowAdapter() {
      public void windowOpened(WindowEvent e) {
        LoginDialog dlg = new LoginDialog(StocksTable.this);
        dlg.show();
        if (!dlg.getOkFlag())
          System.exit(0);

        // Connect to the server
        try {
          // create and initialize the ORB
          String[] args = new String[] 
            { "-ORBInitialPort", "1250", 
              "ORBInitialHost", "localhost" };
          ORB orb = ORB.init(args, null); 
                    
          // get the root naming context
          org.omg.CORBA.Object objRef = 
            orb.resolve_initial_references("NameService");
          NamingContext ncRef = NamingContextHelper.narrow(objRef);
                    
          // resolve the Object Reference in Naming
          NameComponent nc = new NameComponent("MarketData", "");
          NameComponent path[] = {nc};
          m_server = MarketDataHelper.narrow(ncRef.resolve(path));
        } 
        catch (Exception ex) {        
          ex.printStackTrace(System.out);    
          System.exit(0);
        }
        retrieveData();
      }

      public void windowClosing(WindowEvent e) {
        System.exit(0);
      }
    };
    addWindowListener(wndCloser);
        
    setVisible(true);
  }

  // Unchanged code

  public void retrieveData() {
    SimpleDateFormat frm = new SimpleDateFormat("MM/dd/yyyy");
    String currentDate = (m_data.m_date == null ? "7/22/1998" :
      frm.format(m_data.m_date));
    String result = (String)JOptionPane.showInputDialog(this, 
      "Please enter date in form mm/dd/yyyy:", "Input", 
    JOptionPane.INFORMATION_MESSAGE, null, null, 
      currentDate);
    if (result==null)
      return;

    // Unchanged code
  }

  // Unchanged code

  class LoginDialog extends JDialog
  {
    protected JTextField m_nameTxt;
    protected JPasswordField m_passTxt;
    protected boolean m_okFlag = false;

    public LoginDialog(Frame owner) {
      super(owner, "Login", true);
      JPanel p = new JPanel(new DialogLayout2());
      p.add(new JLabel("Name:"));
      m_nameTxt = new JTextField(m_name, 20);
      p.add(m_nameTxt);
      p.add(new JLabel("Password:"));
      m_passTxt = new JPasswordField(m_password);
      p.add(m_passTxt);
      p.add(new DialogSeparator());

      JButton btOK = new JButton("OK");
      ActionListener lst = new ActionListener() { 
        public void actionPerformed(ActionEvent e) {
          m_name = m_nameTxt.getText();
          m_password = new String(m_passTxt.getPassword());
          m_okFlag = true;
          dispose();
        }
      };
      btOK.addActionListener(lst);
      p.add(btOK);

      JButton btCancel = new JButton("Cancel");
      lst = new ActionListener() { 
        public void actionPerformed(ActionEvent e) {
          dispose();
        }
      };
      btCancel.addActionListener(lst);
      p.add(btCancel);

      p.setBorder(new EmptyBorder(10, 10, 10, 10));
      getContentPane().add(p);
      pack();
      setResizable(false);
      Dimension d1 = getSize();
      Dimension d2 = owner.getSize();
      int x = Math.max((d2.width-d1.width)/2, 0);
      int y = Math.max((d2.height-d1.height)/2, 0);
      setBounds(x, y, d1.width, d1.height);
    }

    public boolean getOkFlag() {
      return m_okFlag;
    }
  }

  public static void main(String argv[]) {
    new StocksTable();
  }
}

class ColoredTableCellRenderer extends DefaultTableCellRenderer
{
  public void setValue(java.lang.Object value) {
    // Unchanged code
  }
}

class StockData
{
  // Unchanged code

  public StockData(DataUnit unit) {
    this(unit.getSymbol(), unit.getName(), unit.getLast(), 
      unit.getOpen(), unit.getChange(), unit.getChangePr(), 
      unit.getVolume());
  }
}

class StockTableData extends AbstractTableModel 
{
  // Unchanged code

  public StockTableData() {
    m_frm = new SimpleDateFormat("MM/dd/yyyy");
    m_vector = new Vector();
    //setDefaultData();        No longer used
  }

  public int retrieveData(java.util.Date date, String name, 
   String password, MarketData server) {
    GregorianCalendar calendar = new GregorianCalendar();
    calendar.setTime(date);
    int month = calendar.get(Calendar.MONTH)+1;
    int day = calendar.get(Calendar.DAY_OF_MONTH);
    int year = calendar.get(Calendar.YEAR);

    try {
      DataUnit unit = server.getFirstData(name, password, 
        year, month, day);

      boolean hasData = false;
      while (unit != null) {
        if (!hasData) {
          m_vector.removeAllElements();
            hasData = true;
        }
        m_vector.addElement(new StockData(unit));
        unit = server.getNextData();
      }

      if (!hasData)    // We've got nothing
        return 1;
    }
    catch (Exception e) {
      e.printStackTrace();
      System.err.println("Load data error: "+e.getMessage());
      return -1;
    }
    m_date = date;
    Collections.sort(m_vector, new 
      StockComparator(m_sortCol, m_sortAsc));
    return 0;
  }
}

New instance variables:

At this point you can compile all code and run the Java 2 name server:

tnameserv -ORBInitialPort 1250

Then run our CORBA server:

java MarketDataApp.MarketDataServer

...and wait until it displays a message "Waiting for client connection" in the console. In another session, run our CORBA client:

java StocksTable

Enter the user name and password, "CORBA" and "Swing" respectively (they are displayed by default). Select a date for retrieval of corresponding stock data from the remote CORBA server. This data will be retrieved and displayed in the table.