Learning Client-Server Interaction

Will I need to purchase the J2EE Sun One in order to learn about Client-Server interaction. I have been learning the J2SE , which has introduced me to many new and wonderful exciting possibilities in comparison to C++.
Basically I am going to set up my own small server to practice with Java Servlets to test code that I will eventually learn to produce.
Can anyone help please?
I have no profit intentions, this is an independent learning chat query above. Thanks in advance.

Hi ,
You can download the free trial version of S1AS7 from
http://wwws.sun.com/software/download/app_servers.html.
It is j2ee 1.3 compatible .You can use it to test your servlets
Hope this helps.Get back if you any issues
-Amol

Similar Messages

JSF client-server interaction

Hi,
I would like to create a JSF client application that would be able to modify a text file placed on server
in a different computer on LAN. What all technologies do I need to go through?
Is there any project like this which can help?
please reply with links

Ok , here's the small task.. I only need to modify a file present on server.
I know that ExternalContext.getResourceAsStream() gives input stream which can be used to read the files
but how to write them ?

Client server programming

Hi;
I want to learn client server programming on using windows xp for the client and windows server 2003.
I downloaded the 9.2 windows xp database version for the client . What do I need to download for the server? I see that there is a 32 and 64 bit version for the server.
Thanks for your help!

What I was asking is what should I install on the server
the 32 or 64 bit version of oracle?
I want to learn how to write client/server programs using Oracle.
I have a network at home with one computer serving as the client and another has server 2003 on it.
Again Thanks for your help!

Design Pattern for multithreaded client server program

I asked this question in another post, but with other stuff, so I'll distill this one.
I am creating a multi-threaded client server program (just for learning - a chat program at this point). I built the server and client in swing, and I'm wondering what the best design pattern is for this setup. Right now all the swing stuff is in the MyServer class. In that class I have a loop accepting client connections to the serverSocket and creating a new MyServerThread (threaded client connection).
The problem is that all the work of creating input streams, interacting with the server, all that stuff is done in the MyServerThread class, but I want that text to be written up to the Swing objects - which is in the MyServer class. So right now in the MyServerThread class I pass the MyServer object into it, but I'm not sure if that is really the most robust thing to do. Does anybody have any suggestions as to how this should be done. If somebody has an article they'd like to point to I'll check it out too. But if it's just the run-of-the-mill multithreaded client-server article, I've read alot and most don't specifically address my question.

Thanks for the reply Kaj, and I think I'll keep my design for now, since it's just quick and dirty. I've read the MVC concept a while ago and I'll revisit it again when I get more serious. But I have a question, why should I be using a callback interface, why an interface at all? And then make MyServer implement that interface...why not just pass MyServer to the thread object? Or is there something down the line that I did not forsee?

Client/server program validation - is it possible?

I've been mulling over this problem for a few days, and am starting to wonder if it's theoretically possible to find a solution. I'm not looking for specific code, this probably won't even be implemented in Java, I'm just wondering if there is a theoretical program model that would work in this situation.
The short version:
Validate the data generated by a client program, without knowing the original data.
The long version:
This is a "profiling" system for a MMOG (Massively Multiplayer Online Game). The MMOG is an internet based client/server graphical program where each client connects to the server and they interact with each other and the virtual world. They pay a monthly fee for access to the game. My program is not affiliated with the MMOG or its makers. I have no connections inside the company and cannot expect any cooperation from them.
The "profiling" system is also a client/server model. The client program runs in the background while the MMOG client is active. It accesses the memory of the MMOG client to retrieve information about the player's character. Then, possibly on request or maybe immediately, it sends the character data to our server.
What I want to validate is that the character data being sent is unmodified and actually comes from the MMOG program.
I can reasonably expect that with mild encryption and some sort of checksum or digest, the vast majority of problems can be avoided. However, I am not sure it's possible to completely secure the system.
I assume that the user has access to and knowledge of the profiler client and the MMOG client, their assembly code, and the ability to modify them or create new programs, leveraging that knowledge. I also assume that the user does not have access to or knowledge of either of the server applications - the MMOG server or mine.
In a worst-case scenario, there are several ways they could circumvent any security I have yet been able to think of. For instance, they could set up a fake MMOG client that had the data they wanted in memory, and let the profiler access that instead of the real thing. Or, they could rewrite the profiler to use the data they wanted and still encrypt it using whatever format I had specified.
I have been considering using some kind of buffer overflow vulnerability or remote execution technique that would allow me to run specific parts of the client program on command, or get information by request, something that could not be anticipated prior to execution and thus could not be faked. But this seems not only insecure for the client but also not quite solid enough, depending on how it was implemented.
Perhaps a series of apparently random validation codes, where the client does not know which one actually is doing the validation, so it must honor them all. Again, this is very conceptual and I'm sure that I'm not explaining them very well. I'm open to ideas.
If I don't come up with anything better, I would consider relying on human error and the fact that the user will not know, at first, the relevance of some of the data being passed between client and server. In this case, I would include some kind of "security handshake" that looks like garbage to the client but actually is validated on the server end. A modified program or data file would result in an invalid handshake, alerting the server (and me) that this client was a potential problem. The client would have no idea anything had gone wrong, because they would not know what data the server was expecting to receive.
I hope I have not confused anyone too much. I know I've confused myself....

Yes, that is the general model for all MMOGs these days - no data that can actually affect the game is safe if loaded from the client's computer. All character and world data is sent from server to client and stored in memory. Any information that is saved to the client's computer is for reference only and not used by the game engine to determine the results of actions/events etc.
My program accesses the MMOG client's memory while the game is running, and takes the character information from there. It does not have direct access to the MMOG server, and does not attempt to modify the data or the memory. Instead, it just encrypts it and sends it to our server, where the information is loaded into a database.
The security issue comes into play because our database is used for ranking purposes, and if someone were to hack my program, they could send invalid data to our servers and affect the rankings unfairly.
I'm just trying to think of a way to prevent that from happening.

Client/Server hang up?

I'm writing a basic client server program. I created an ArrayList to hold all the sockets of a connection so each client could, hopefully, eventually interact.
Right now my client is a text field with a text area under it. A user types a command up top and then hits enter and sends that along to the server. However when i send in the message it seems to hang up and never sends back a reply. But what's really odd about it, is that if i close my server window and there by shutting it down the client then outputs exactly what i expected it to if it was working right. So im curious why there's this hangup in my code?
Server:
import java.awt.BorderLayout;
import java.awt.Font;
import java.io.IOException;
import java.net.InetAddress;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.ArrayList;
import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
public class Server extends JFrame{
          private JTextArea jta = new JTextArea();
          private static ArrayList<Socket> clients = new ArrayList<Socket>();
          public Server(){
               getContentPane().setLayout(new BorderLayout());
               getContentPane().add(new JScrollPane(jta), BorderLayout.CENTER);
               jta.setFont( new Font( "Times", Font.BOLD, 20));
               setSize(500, 300);
               setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
               setVisible(true);
               try{
                    setTitle("Server: " + InetAddress.getLocalHost().getHostName());
                    int clientNo = 1;
                    ServerSocket serverSocket = new ServerSocket(0);
                    jta.append("Port: " + serverSocket.getLocalPort() + "\n");
                    while(true){
                         Socket socket = serverSocket.accept();
                         InetAddress inetAddress = socket.getInetAddress();
                         clients.add(socket);
                         World thread = new World(socket);
                         jta.append("Connected with client :" + clientNo + "\n");
                         thread.start();
                         clientNo++;
               }catch(IOException ex){
                    System.err.println(ex);
          public static void main(String[] args){
               new Server();
          public static ArrayList getClients(){
               return clients;
     }World:
import java.io.IOException;
import java.io.PrintWriter;
import java.net.InetAddress;
import java.net.Socket;
import java.util.ArrayList;
import java.util.Scanner;
public class World extends Thread {
     private Socket mySocket;
     private int myPort;
     private InetAddress myInetAddress;
     private String myHostName;
     private ArrayList<Socket> theClients;
     public World(Socket newSocket) {
          mySocket = newSocket;
          myPort = mySocket.getPort();
          myInetAddress = mySocket.getInetAddress();
          myHostName = myInetAddress.getHostName();
     public void run() {
          String test;
          Scanner input = null;
          PrintWriter output = null;
          try {
               String fileName;
               input = new Scanner(mySocket.getInputStream());
               output = new PrintWriter(mySocket.getOutputStream(), true);
          }catch(IOException e){
          output.println("Please Enter Command");
          while((test = input.nextLine()) != null){
               if(test.contains("get clients") ){
                    theClients = Server.getClients();
                    for(int i = 0; i < theClients.size(); i++){
                         output.println(theClients.get(i).getInetAddress().getHostName());
                    output.flush();
               }else{
                    output.println("not sure");
                    output.flush();
}Client:
import java.awt.*;
import java.awt.event.*;
import java.io.*;
import java.net.*;
import java.util.Scanner;
import javax.swing.*;
public class Client extends JFrame implements ActionListener{
     private JTextField jtf;
     private JTextArea jta = new JTextArea();
     private PrintWriter output;
     private Scanner input;
     public Client(String host, int port){
          JPanel p1 = new JPanel();
          p1.setLayout(new BorderLayout());
          p1.add(jtf = new JTextField(10), BorderLayout.CENTER);
          jtf.setHorizontalAlignment(JTextField.RIGHT);
          jtf.setFont(new Font("Times", Font.BOLD, 20));
          jta.setFont(new Font("Times", Font.BOLD, 20));
          getContentPane().setLayout(new BorderLayout());
          getContentPane().add(p1, BorderLayout.NORTH);
          getContentPane().add(new JScrollPane(jta), BorderLayout.CENTER);
          jtf.addActionListener(this);
          setSize(500,300);
          setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
          setVisible(true);
          try{
               setTitle("Client: " + InetAddress.getLocalHost().getHostName());
               Socket socket = new Socket(host, port);
               input = new Scanner(socket.getInputStream());
               output = new PrintWriter(socket.getOutputStream(), true);
               jta.append(input.nextLine() + "\n");
          }catch(IOException ex){
               jta.append(ex.toString() + "\n");
     public void actionPerformed(ActionEvent e){
          String nextLine;
          String findFile = jtf.getText().trim();
          ((JTextField)(e.getSource())).setEditable(false);
          if ( e.getSource() instanceof JTextField){
                    jta.append("Getting file: \"" + findFile + "\" \n");
                    output.println(findFile);
                    output.flush();
                    while(input.hasNext()){
                         nextLine = input.nextLine();
                         jta.append(nextLine + "\n");
     public static void main(String[] args){
          int portSend;
          if (args.length != 2){
               System.out.println("not Enough arguments");
               System.exit(-1);
          portSend = Integer.parseInt(args[1]);
          new Client(args[0], portSend);
}

Don't run networking code in the constructor. Start a separate thread for the accept loop.

Client-server database application...

Hi there!
I'm about to write a database-application and I wonder if the following approach is to prefer or not:
I want to use a MySQL-database and there shall be about eight client-applications which all shall be able to use it. I think of solving the above with RMI (I want to create/deploy a server wich will contain all the different SQL-queries on the same site as where I install the MySQL-database ). From the clients I just, with RMI, invoce the methods on the server which contains the different queries I want to use. In other words all the database-functionality is located on the server somewhat like stored procedures. To make it work each client must be assigned a thread of its own on the server...is this right?
The advantages of the above which I can think of is: I just need to stuff one J/Connector driver in the JRE (on the server). Another is that I can use the nameservice of RMI... are there others?
Is the above a good / usual or even bad approach?
Is it more usual or even better to just provide the database-functionality (SQL-queries) in the clients and provide every client with the J/Connector driver?
Thanks in advance!

You noted that there will be "eight client-applications" - does that refer to eight users or eight programs using the database? This is important in determining your course of action.
If you're talking about a small number of concurrent users (you have to define small), then you'll probably better off trying to do all the data/business logic in the app. If you're talking about a large number of concurrent users (again, your definition), your client/server paradigm might be better.
To complicate things, unless you're doing this as a learning-on-your-own project (e.g. not getting paid for it), this is where you might want to evaluate using J2EE technoligies for your server-side implementation. Writing your own server is not a trivial task (been there, done that - pre-J2EE, of course): there's a lot of things you have to figure out how to handle. Well, that's true of even using J2EE, but there's some portion of what your server would need to do already taken care of in an application server.

OLE Alternatives in Forms 6i Client Server

I'm fishing for some advice and maybe some examples of how to get around an OLE issue that's adversely affecting an upgrade project.
We're currently migrating a Forms 4.5 application to 6i. This application displays MS Word documents (OLE Container) that are stored in the database and uses OLE to open manipulate, and save the documents back to the database. We've come across some serious problems with OLE and 6i that don't look like they'll be fixed any time soon (bug #2615804 in particular).
Since OLE (ActiveX) is not supported a web delivered configuration, we're looking at an alternative to interacting and storing Word documents using a client/server configuration. This will have the added bonus of making the move to web delivery once we decide to go down that path.
Has anyone out there had any good experience with overcoming this OLE problem? It seems like every pre-Forms 9i book out there has touted OLE as a way of interacting with Office tools and now OLE has become a roadblock.
I've had a look at the JACOB example, but that doesn't really help if you're not deploying via the web.

With the beans you've looking at visual stuff : like the look and feel project
With the importer it's more like leveraging java functionality : in my case I've just implemented a call to a webservice on an application server. There is nothing visual here and it's just called via a straight bit of PL/SQL that call my java classes ( however, in that case I could also use UTL_HTTP directly to make the call and thus not bother with java importer - but the database wouldn't allow UTL_HTTP calls :( )
For both of these you'd need to tell forms where to find the JAR file in it's java environment - but you won't have that in c/s
Another way is to load up java code into the database and process it within the database and hide it completely from Forms. I've done this sort of thing loading Apache-FOP into Oracle and creating PDF files in the database (as BLOBS) from XML/XSL also in the database as XMLTYPES.
At least that's my view on how it fits together ... maybe others know more :)
Steve

FRM-40735 on the Web, in client/server without error

We have 2 types of Form modules.
Type 1 are simple multirecord modules,
which uses PL/SQL library module PL1.plx.
Type 2 are complex (master-detail) modules,
which uses PL/SQL library module PL2.plx.
In client/server, both types of Form modules work fine.
On the Web (Intranet), type 1 modules works fine, but loading of type 2 modules finishes with error: FRM-40735 PRE-FORM trigger raised unhandled exception ORA-06508.
In both cases database schema and fmx/plx modules are the same.
Implementation of WebForms is noncartridge
(without Oracle Application Server).
Clients use Jinitiator and IE4.
Forms version is 5 + patch 7.
DBMS version is 7.3.4.0.
Thanks and regards.

Two questions:
Are you running your application against one DB, while it was compiled against another?
If any of your forms or libraries is calling DB stored package that are passing parameters in between database and modules?
If the answer to both questions is yes, then you're dealing with Oracle bug. Oracle support points to interaction between forms
PL/SQL 8.0.5.1.0 and database PL/SQL 2.3.4.
This problem should be fixed in the forms
PL/SQL 8.1.6 which is not available at present time. The only work around is to maintain forms executable and/or compiled libraries for each of your DB.
Good luck.
null

D2k in client server mode & web environment

Hi friends,
I am using forms 6i with oracle 9i. I have a couple of questions, please advice.
I have developed couple of forms in client server mode and this would be added to an existing application. I have been informed now that the application is web based. I have no idea about how a form can be coded_for or deployed_in web based environment.
Is there any provision to convert the forms developed in client server mode so that we can use it in web based application ?
what is the effort required in doing this conversion ?
Do we have any docs for using d2k forms in a web environment ?
Plz feel free to point out if I have missed any detail without which it is difficult to answer this question.
Thanks
-vish

Hello,
It is very easy to migrate from C/S to web, because of the portabilty of the Forms design code (.fmb)
All you have to do, is to recompile the modules with the new binaries. The only "but" is that some instructions have been depreciated, and you have to rewrite them (often client machine interactions, that are covered by the Webutil library).
goto the OTN Forms home page, then click the Migration link.
Francois

ActiveX Bridge Usage in Client-Server architecture

Hi,
We developed an application (client-server architecture) based on RMI layer. Now we want to expose client as an ActiveX Control. Assume, server is running on one m/c, client is running on different m/c. Now in other m/c, on VB container my client activex is running. This activex should fetch data from server(through java based client) and should display it.
We implemented an activex control for client, it is interacting with server. To show server data it should use one user-defined object class. We made this object as public static. But we are not able to use this object on activex side. Even serializing this object and reading it again is also not working.
If anyone has idea on debugging this issue, please help us.
Sagar.

Use the 'NI AlarmEvent Browser' ActiveX control. Set the machine as the remote station. Lots of parameters.
Mike
Mike Crabtree - Lead Developer
Destek of Nevada, Inc. / Digital Telemetry Systems, Inc.
(866) 964-6948 / (760) 247-9512

Authetication problem in client/server app

I am presently developing a client/server program, and I'm wondering what will be the best form of authentication. I plan to develop a protocol for the programs, any deviation leading to socket closure. I thought about signatures, but I don't think any body's ready to vouch for me(ie I don't know how to go about signatures). Is there any help?

Learn about JAAS

JavaFX as a SaaS/ How good is it for Client-Server work?

I was under the impression that FX could be used to produce a Client-Server application as well as SaaS.
a member of another forum said "I'm sure you meant to say "Desktop". JavaFX will not be making inroads on the web as a client-side technology."
To which I said
There have been examples of FX used with EE
http://www.oracle.com/technetwork/java/javafx/samples/index.html
http://docs.oracle.com/javafx/2/overview/jfxpub-overview.htm
Sales Dashboard (DataApp)
DataApp is a client-server application for a fictional global automobile company called Henley Car Sales. Automobile sales are simulated on an EJB server using JavaDB, and the data is available via Derby and a RESTful web service. The client demonstrates a variety of data presentations by using a mix of FXML and JavaFX.
I thought originally that JavaFX was "Desktop" only also, until I found this example. I couldn't get it to run due to some weird Database line read issue that others also had. I'm not sure if this is now due to FX's integration, or if this was something new, but I believe I have seen another FX client-server app as well.
I'm not that familiar with the client-server side of Java yet, so if you have other Information I would like to know, because I am looking to design a Client-Server app with FX, and I don't see why it would be an issue, unless there are huge limitations."
He ended up saying "Those are still desktop apps. Sure, they are client-server in that they connect to a remote database. But they are still traditional fat-client apps rather than web-based thin-client SAAS web applications which, these days, most people will think of when you say "client".
My point is to be more precise when you use the word "client".
But if your point is just that JavaFX is taking over from Swing for the limited areas in which Swing is used, I have no insight into that area."
Now I don't really like attitudes when I get my question answered, but the high and mighty needs to stop. It clearly says Client-Server so I don't know why it's being denounced by this dude who thinks he obviously knows better.
Anyways he talks about it only being able to connect to a DB, to which it says it uses EE tech such as EBJ, Restful, and Derby, so that's more than just DB right(I don't know since I havent' learned that yet)?
It seems as if he's saying that only EE code can go up on a server? Or can SE code go up there as well?
I'm looking to design a SaaS software with FX, so if this isnt' possible I would like to know possible other options(or just having all of the gui work on the client, and the rest on the backend)???
Thanks!
~KZ
Edited by: KonradZuse on Apr 30, 2013 11:26 AM

This response is not a tutorial, I hope it gives you some verbiage to use in further searches.
SaaS to me means that the service is running on the server. If you have the server and permission to run java apps there then you can use Java FX by having the server shuttle requests to the Java FX app. But this is probably not the intent of Saas (it would be more appropriate to use a java implemented web service).
If you are using Netbeans then it is very easy to create demo projects; use "File/New Project" to run them on your local computer.
Example File/New Project/Java Web/Web Application will give you a hello world web site very quickly. This will 1) start either tomcat or glassfish as the server. 2) launch an html page with "hello world". then you can use java script to talk with the server via ajax. Using this approach you are going to need to study JSP or J2EE stuff.
After this is running you could start one of the Java Fx examples in Netbeans: File / New Project / Samples / WebViewBrowser. This will start a javaFX app that acts like a browser and runs on the client.
So, start the "hello world" app in netbeans by right clicking it in the project pain and selecting "debug". Then start the webviewBrowser app the same way to load that web page that has "hello world" in it as all browsers do. In the WebviewBrowser (which is java fx) you can get at the javascript in the web page and do all kinds of stuff. You'll need to search for webviewBrowser examples.
The above all assumes a Netbeans solution. But, as you probably know, there are no rules. The server can be in C++ and the client in C (or any other language). The server and client usally communicate via http or tcp. So you could have a server written in java (maybe J2ee or you can rewrite a http server from scratch which isn't that hard - search for "HttpServletRequest and HttpSession" ) and the client can be in Java FX (where the Java FX talks directly with the server via http (no javascript or web page in the middle) again there are probably hundreds of libraries to talk to a http server).
I use HttpServletRequest and HttpSession on the server side with MySQL and xml. On the client I use javaScript but I am moving to a strictly Java FX solution. This will give me close to 100% java on both sides and for my purposes this will work. (I may need a little html in the middle for drag and drop installation.) I am hoping that work continues with porting Java FX to most devices: Android, IOS, WinPhone. It is already on Linux, Windows Desktops and Mac.
Edited by: KevinPas on May 1, 2013 9:50 AM
Edited by: KevinPas on May 1, 2013 9:56 AM

Need help in desigining Client/Server Application using Java

Hi,
I am new to Java and no sooner that I started studing it I have been given a project - client server java Application that allows a user to do a property search based on critiras (eg location, price) and display the results. I am stuck because I don't know where I need to start. Have to use IDE (Netbeans or Eclipse) but not sure about dev frameworks.
Can someone give me an outline of what I should do / where I should start? What will be the best solution?
Thanks in adance

http://java.sun.com/docs/books/tutorial/networking/index.html
That's Sun's networking tutorial series. Live it, learn it, love it. You'll need to decide if you want to use connected sockets or datagrams. You'll need details like, can multiple clients connect simultaneously?
The tutorials are the first step though.

Basic Client-Server query

I'm in the early stages of writing a client-server program. I've got the client and the server communicating (I think). I send text from the client to the server. I then want the server side BufferedReader in to be read into a variable. I've tried doing it using String inputLine = in.readLine() but it keeps throwing an IOException. I can't work out why.
try {
            PrintWriter out = new PrintWriter(clientSocket.getOutputStream(), true);
            BufferedReader in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
         System.out.println("The printwriter and bufferedreader have been set up.");
            String inputLine, outputLine;
            inputLine = in.readLine();
            System.out.println(inputLine);
        } catch (IOException e) {
            System.out.println(e);
        }The serverSocket and socket have been set up properly as far as I can tell. It's just the above portion of code that seems to be causing a problem. My knowledge of Java is fairly basic at the moment, so any help would be greatly appreciated.

I agree that jdbc is probably the simplest approach here and it is probably the best introduction to java/database interaction. If you put some forethought into the design then it will also take some time out of transitioning to RMI should you decide to go that route. Is there a reason jdbc won't work for your application?
Oracle's JDBC download:
[http://www.oracle.com/technology/software/tech/java/sqlj_jdbc/index.html]
Oracle JDBC FAQ:
[http://www.oracle.com/technology/tech/java/sqlj_jdbc/htdocs/jdbc_faq.htm]
You can find lots of tutorials on connecting, querying, etc. via google as well.
RMI may help keep the client smaller and also gives some flexibility but if these (remote) methods are only going to be used for this application then once again jdbc may be the best choice. If there is a possibility that other applications may use them in the future then it might be a good choice.
[http://java.sun.com/j2se/1.5.0/docs/guide/rmi/hello/hello-world.html]

Learning Client-Server Interaction

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