Simple distribuited computing appl. with RMI (message-passing system ?)

Question

hi,
I had success with several exercises to create remote objects, and now
I would like to apply RMI mechanism to work in my application on a small net.
My problem is to make the connection to a database (derby) embedded
in a copy of the application (installed as server) ,accessible  to other copies
of the same application (installed as clients).
I studied the problem and, in my simple mind of beginner,
I understood that for it to work (as first) it is necessary to create a system
of messaging communication between the agents on the net, to allow the clients
applications know the name of object they have to use...
I don't know if my idea is correct, and I am not sure if this is the right direction
to begin the new part of my work ...
Before beginning my work here, I should like to read some tutorial
or read some other type of information  that can guide me to go
forward in this new problem.
Any help should be appreciated.
thank you
regards
tonyMrsangelo

Answer 1

hi Peter ,
thank you for answering me,
I read the Derby documentation (Derby Developer's Guide) where is wrote:
When a Derby database is embedded in a Java application, the database is dedicated to that single application.
If you deploy more than one copy of the application, each application has its own copy of the database and Derby software. I am not sure to 100%, but think to interpreter those words in the way that different applications cannot share the same information on the tables of an only one dataBase...
For this reason I decided to use Remote Objects to access to database.
I think that, for my simple case, it is enough to implement a communication using a ServerSocket and a Socket.
Now I have difficulty with this problem...
I wrote two small programs to manage the communication between a Socket and a ServerSocket.,
but I am not able to do they work correctly.
I post here the code of both .. I would like to know what is wrong because they don't communicate each the other.
Implementation of the program Server :
* this class implements a simple Gui
public class ServerXnetworkingTest extends JFrame {
// I cannot write the code here because the number of characters allowed
} // class ServerXnetworkingTest
class SocketServerImplementation {
    Socket socket;
    int portNmbr = 4444;
    BufferedReader inStream = null;
    PrintWriter outStream = null;
    ServerXnetworkingTest serverXnetworkingTest;
     * @param serverXnetworkingTest
    public SocketServerImplementation(ServerXnetworkingTest xxx) { // constructor
        serverXnetworkingTest = xxx;
        ServerSocket serverSocket = null;
        try {
            serverSocket = new ServerSocket(portNmbr);
        } catch (IOException ex) {
            Logger.getLogger(SocketServerImplementation.class.getName()).log(Level.SEVERE, null, ex);
        // Waits the connection of the client
        // (dice al programma di aspettare per un tempo indefinito fino a quando
        // un cliente non si connette alla porta).
        Socket incoming = null;
        try {
            incoming = serverSocket.accept();
        } catch (IOException ex) {
            Logger.getLogger(SocketServerImplementation.class.getName()).log(Level.SEVERE, null, ex);
        //  After a connection is set with this port,:
        // - una richiesta attraverso la rete questo metodo restituisce
        //   un oggetto Socket che rappresenta la connessione che e' stata stabilita.
        // - si puo' utilizzare questo oggetto per ottenere gli steram di input
        //    e di output, come sotto indicato.
        try {
            inStream = new BufferedReader(new InputStreamReader(socket.getInputStream()));
            outStream = new PrintWriter(socket.getOutputStream(), true);
        } catch (IOException ex) {
            Logger.getLogger(ServerXnetworkingTest.class.getName()).log(Level.SEVERE, null, ex);
        String inputLine;
        try {
            while ((inputLine = inStream.readLine()) != null) {
//                JOptionPane.showMessageDialog(serverXnetworkingTest, msg);
                System.out.println("Server ----> letta linea di testo = " + inputLine);
        } catch (IOException ex) {
            Logger.getLogger(SocketServerImplementation.class.getName()).log(Level.SEVERE, null, ex);
//        outStream.print(inputLine);
//        outStream.flush();
    } // constructor
     * this function is  called pushing a button to write text in the output stream
     * @param msg
    void messageSender(String msg) {
        outStream.print(msg);
        outStream.flush();
       // outStream.write(msg); // ???
        //outStream.flush();       // ???
    } // stringMsgSender()
} // class SocketServerImplementation {
Implementation of the program Client :
* this class implements a simple Gui
public class ClientXnetworkingTest extends JFrame {
// I cannot write the code here because the number of characters allowed
} // class ClientXnetworkingTest
class SocketClientImplementation {
    Socket socket;
    int portNmbr = 4444;
    BufferedReader inStream = null;
    PrintWriter outStream = null;
    ClientXnetworkingTest clientXnetworkingTest;
     * @param serverIpAddress
     * @param xxx
    public SocketClientImplementation(String serverIpAddress, ClientXnetworkingTest xxx) { // constructor
        clientXnetworkingTest = xxx;
        outStream = null;
        inStream = null;
        try {
            // constructor
            socket = new Socket(serverIpAddress, portNmbr);
        } catch (UnknownHostException ex) {
            Logger.getLogger(ClientXnetworkingTest.class.getName()).log(Level.SEVERE, null, ex);
        } catch (IOException ex) {
            Logger.getLogger(ClientXnetworkingTest.class.getName()).log(Level.SEVERE, null, ex);
        // http://forums.sun.com/thread.jspa?forumID=31&threadID=595806
        // trovato con : use InputStream with Strings
        try {
//            inStream = socket.getInputStream();
            inStream = new BufferedReader(new InputStreamReader(socket.getInputStream()));
            outStream = new PrintWriter(socket.getOutputStream(), true);
        } catch (IOException ex) {
            Logger.getLogger(ClientXnetworkingTest.class.getName()).log(Level.SEVERE, null, ex);
    } // constructor
     * this function is called pushing a button to write text in the output stream
     * @param msg
    void messageSender(String msg) {
        outStream.print(msg);
        outStream.flush();
     //   outStream.write(msg); // ???
     //   outStream.flush();       // ???
    } // stringMsgSender()
} // class SocketClientImplementation {any help is welcome
thank you
regards