Java sockets - Custom Objects Sending

Question

I have created working sockets, and when I try to send text or numbers, its ok, but when im trying to send my custom class object, i got NullPointerException... Here is some code:

public boolean SendLi(List<Entity> list)
{
    try {
         out.writeObject(list);
    } catch (IOException e) {
        e.printStackTrace();
        System.err.println("Send: Error on OutputStream.write(byte[])");
    }
    return true;
}

public List<Entity> RecvLi()
{
    List<Entity> data;
    data = new ArrayList<Entity>();
      try{
          data = (List<Entity>) in.readObject();
        } catch (IOException e) {
          System.err.println("Send: Error on OutputStream.read(byte[]) - IOException");
          return null;
        } catch (ClassNotFoundException e) {
          System.err.println("Send: Error on OutputStream.read(byte[]) - ClassNotFound");
            e.printStackTrace();
        }
    return data;
}

Actually, that code I made for Lists, but I want to have some simmilar functions to send other objects. Thanks for any replies!

Rajesh Pantula · Accepted Answer · 2012-01-12 12:21:38Z

1

You need to Serialize your Custom class before sending it through socket.The object that you are sending in

out.writeObject(list);

should be serialized, your class should implement java.io.Serializable interface

answered Jan 12, 2012 at 12:21

Rajesh Pantula

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2 Comments

noisy cat Over a year ago

The problem is that the custom objects are serialized, but it doesnt help. I cant serialize ArrayList, so it must be something other...

Ventsislav Marinov Over a year ago

Instead List<Entity> try to set array Entity[].

Baatar · Accepted Answer · 2012-01-12 12:41:11Z

Code snippets below works with all kind serializable objects for me. Please check.

*IRequest is object to send. *IResponse is object to get.

Client Code:

    Socket clientSocket = new Socket(hostName, portNo);
    clientSocket.setSoTimeout(connectionTimeout);
    try {
        OutputStream outputStream = clientSocket.getOutputStream();
        InputStream inputStream = clientSocket.getInputStream();
        ObjectOutputStream objOutputStream = new ObjectOutputStream(outputStream);
        ObjectInputStream objInputStream = null;

        try {
            objOutputStream.writeObject(request);
            objOutputStream.flush();
            objInputStream = new ObjectInputStream(inputStream);
            res = (IResponse) objInputStream.readObject();
        } finally {
            if (objOutputStream != null) {
                objOutputStream.close();
            }
            if (outputStream != null) {
                outputStream.close();
            }
            if (objInputStream != null) {
                objInputStream.close();
            }
            if (inputStream != null) {
                inputStream.close();
            }
        }
    } finally {
        clientSocket.close();
        clientSocket = null;
    }

Server Code:

        private IMessageProcessor messageProcessor = null;
        private Socket clientSocket = null;
        private Logger logger = null;


        String clientIP = clientSocket.getInetAddress().getHostAddress();
        int clientPortNr = clientSocket.getPort();

        InputStream inputStream = clientSocket.getInputStream();
        OutputStream outputStream = clientSocket.getOutputStream();
        try {
            ObjectInputStream objInputStream = null;
            ObjectOutputStream objOutputStream = null;
            try {
                IRequest request = null;

                objInputStream = new ObjectInputStream(inputStream);
                objOutputStream = new ObjectOutputStream(outputStream);
                request = (IRequest) objInputStream.readObject();

                IResponse response = null;

                try {
                    response = messageProcessor.processMessage(clientIP,
                                                                clientPortNr,
                                                                request,
                                                                logger);
                    objOutputStream.writeObject(response);
                } catch (Exception ex) {
                    objOutputStream.writeObject(ex);
                }

                objOutputStream.flush();
                objOutputStream.reset();

            } finally {
                if (objInputStream != null)
                    objInputStream.close();
                if (objOutputStream != null)
                    objOutputStream.close();
            }
        } finally {
            inputStream.close();
            outputStream.close();
            clientSocket.close();
        }
    } catch (Exception ex) {
        logger.error(ex.getMessage());
    }

I guess there is something wrong on your side because I use it everyday. Maybe first you should try to transfer a simple Integer object. There can not be any problem with it.

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