Question

snippet from The Server code :

 public void run() {
        try {
          // Create data input and output streams
          ObjectInputStream inputFromClient = new ObjectInputStream(
            socket.getInputStream());
          ObjectOutputStream outputToClient = new ObjectOutputStream(
            socket.getOutputStream());

          while (true) {

         cop = inputFromClient.readObject();

         String[][] m1=new String[][] {{"1", "1","1"}};
         Object xx=new getSerialModel(m1);
         outputToClient.reset();
         outputToClient.writeObject(xx);

         outputToClient.flush();


          }
        }

snippet from the Client :

//////////////
    /// sockt jop
    try {
    // Create a socket to connect to the server
   socket = new Socket("127.0.0."+Math.round(50+Math.random()*50), 8000);

    // Create an output stream to send data to the server
   toServer = new ObjectOutputStream(socket.getOutputStream());
   toServer.flush();

  }
  catch (IOException ex) {
    msgArea.append('\n' + ex.toString() + '\n');
  }
///////////////////
//***
///////////////////
buttonSave.addActionListener(new ActionListener()

{ public void actionPerformed(ActionEvent ev)

{

System.out.println("Saving data is not implemented yet.");
        String[][] m1={{"0","0","0"}};
        for ( int i = 0 ; i < tableModel.getRowCount() ; i++ ){
            { for ( int j = 0 ; j < tableModel.getColumnCount() ; j++ )
                    m1[i][j]=(String)tableModel.getValueAt(i, j) ;
            }
        }

        getSerialModel obt =new getSerialModel(m1);

        try{
            toServer.reset();
        toServer.writeObject(obt);
       toServer.flush();


        }
        catch (Exception ex) {
     msgArea.append("cant reach the server its may be off" + '\n');
   }

}

});
// button send msg
    buttonsendtest.addActionListener(new ActionListener()

{ public void actionPerformed(ActionEvent ev)

{
        try{


       fromServer = new ObjectInputStream(socket.getInputStream());

       Object mdata = fromServer.readObject();
       tableModel.setDataVector((((getSerialModel)mdata).getmodel()), columnNames);
       table.updateUI();

        }
        catch (Exception ex) {
            System.out.print(ex.getStackTrace());
     msgArea.append("cant reach the server its may be off "+ ex.toString() + '\n');
   }

}
});

When I try to read serializable object from the server multible times , I get this exception , for first time the reciever read it successfully .

java.io.StreamCorruptedException: invalid stream header: 00007571

how can I fix it ?

Answer 1

If you are creating multiple ObjectInputStream instances in series for the same socket input stream, this seems like a bad idea. If the server is writing multiple objects to the same output stream, then there is serialization-related information that only gets sent once per unique object, and only the first ObjectInputStream instance on the client would be able to reliably read this. Using only one ObjectInputStream instance per socket input stream and one ObjectOutputStream instance per socket output stream is probably the safest implementation.

Also, if you are writing multiple objects to the same ObjectOutputStream instance on the server side (i.e., multiple writeObject() calls), this can result in stream header problems due to potentially multiple references to the same objects (typically nested references) when they are read by the client’s input stream

This problem occurs when the object output stream wraps a socket output stream since during normal serialization, the second and later references to an object do not describe the object but rather only use a reference. The client’s ObjectInputStream does not reconstruct the objects properly for some reason due to a difference in the header information it is expecting (it doesn’t retain it from previous readObject() calls); this only seems to happen with socket streams, not file I/O, etc. This problem does not occur with the first readObject() call but rather the second and subsequent ones.

If you want to continue to use the same socket stream to write multiple objects, you will need something like the following in the server code:

objectOut.reset()
objectOut.writeObject(foo);

The reset() call re-initializes the stream, ignoring the state of any objects previously sent along the stream. This ensures that each object is sent in its entirety without the handle-type references that are typically used to compress ObjectOutputStream data and avoid duplication. It’s less efficient, but there should be no data corruption when read by the client.