Help on Serializable

[Bill Robertson]

I have a simple class:

 class TestCommand implements java.io.Serializable {

int total = 5;


} 

That I write from a client to a server.
The client simply uses an ObjectOutputStream wrapped around
a socket and performs a writeObject(tc);
Ex.

TestCommand tc = new TestCommand();
ooStream.writeObject(tc);  

The server simply uses an ObjectInputStream to read in
the object.

  
TestCommand obj = (TestCommand) ois.readObject();

Here is my question. When I declare my class TestCommand without
any instance variables it works fine. But then when I give it
a variable, in this case total, I get a dump. Why??
I tried to use defaultWriteObject() and defaultReadObject() but still
received dump - although a different exception.

[Ernest Friedman-Hill]

You should always call flush() on an ObjectOutputStream before trying to read an object from the other end of a pipe like this. That should fix the problem here.

[Bill Robertson]

Still gives me the same old exception. Thank you though!!!

[Ernest Friedman-Hill]

OK, well... you didn't tell us what the actual exception is, so I'm just guessing. What does the stack dump say? Does the client have access to the same .class file as the server? Make sure it's not a version-mismatch problem (many people seem to think the .class file is serialized with the data -- this is untrue.)

[Bill Robertson]

Here I have included more than what you probably want. Client, Server,
and Object code, and the exception.

THE CLIENT:

 
package testx.tests;
import java.net.*;
import java.io.*;
public class ClientTest {
public static void main (String[] args) {

    String host = args[0];
    int port = Integer.parseInt(args[1]);
    try {
        Socket socket = new Socket(host,port);
ObjectOutputStream ooStream; 
ooStream = new ObjectOutputStream(socket.getOutputStream());
        ooStream.writeObject(new ObjectTest());
        ooStream.flush();
    } catch (Exception ex) {
System.out.println("Bill it did not work");
    }
  }
}
 

THE SERVER:

  
package testx.tests;
import java.net.*;
import java.io.*;
public class ServerTest {
 
    ServerSocket serverSocket;
    Socket clientSocket;
    private ObjectInputStream ois = null;

    public static void main(String [] str) {
        ServerTest server = new ServerTest();
server.begin(str[0]);
    }

    private void begin(String strPort) {
        try {
    int port = Integer.parseInt(strPort);
    serverSocket = new ServerSocket(port);
        clientSocket = serverSocket.accept();
        } catch (IOException e) {
            System.out.println("Could not start server.");
            e.printStackTrace();
        System.exit(-1);
}
try {
           ois = new ObjectInputStream(clientSocket.getInputStream());} catch (IOException e) {
            System.out.println("Could not open IO streams.");
       e.printStackTrace();
        System.exit(-1);
}
        try {
    System.out.println("00000");
    Object ot =  ois.readObject();
    System.out.println("1111111");
        } catch (Exception ioex) {
    System.out.println("Socket error: " + ioex.getMessage());
       ioex.printStackTrace();
        System.exit(-1);

        }
    }
}

THE OBJECT:

  
package testx.tests;
public class ObjectTest implements java.io.Serializable {

int total = 4;

}

THE EXCEPTION:

Socket error: Connection reset
java.net.SocketException: Connection reset
at java.net.SocketInputStream.read(SocketInputStream.java:168)
at java.io.ObjectInputStream$PeekInputStream.read(ObjectInputStream.java:2150)
at java.io.ObjectInputStream$BlockDataInputStream.read(ObjectInputStream.java:2558)
at java.io.ObjectInputStream$BlockDataInputStream.readFully(ObjectInputStream.java:2582)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:1834)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1769)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1646)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1274)
at java.io.ObjectInputStream.readObject(ObjectInputStream.java:324)
at testx.tests.ServerTest.begin(ServerTest.java:58)
at testx.tests.ServerTest.main(ServerTest.java:22)

[Ernest Friedman-Hill]

This code should work perfectly, except for one thing: the client exits right after sending the data, without closing the stream, and this may leave the server surprised to find the connection abruptly terminated. To confirm this, add a "Thread.sleep(5000)" after the flush call in the client, and see if the problem clears up.

[Bill Robertson]

Yes!!! You are exactly correct. How do I correct the code and can you
give a little more explanation.

[Bill Robertson]

But, I just thought of something, this does not explain why
it would work everytime with an object that did not have instance
variables. In otherwords, how does the instance variable come into
play?