ObjectOutputStream: Sending the same but modified Object twice

Question

Using the Windows JRE1.6_05 or the JRE 1.6 on Mac OS X and the following code for the client:
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.net.Socket;
public class Client {
     public static void main(String[] args) throws Exception {
          Socket s=new Socket("127.0.0.1",5000);
          ObjectOutputStream oos= new ObjectOutputStream(s.getOutputStream());
          StringBuffer sb=new StringBuffer("foo");
          oos.writeObject(sb);
          sb.replace(0, sb.length(), "bar");
          oos.writeObject(sb);
}and the following code for the server
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.net.ServerSocket;
import java.net.Socket;
public class Server {
     public static void main(String[] args) throws Exception {
          ServerSocket ss=new ServerSocket(5000);
          Socket s= ss.accept();
          ObjectInputStream ois= new ObjectInputStream(s.getInputStream());
          StringBuffer sb=(StringBuffer)ois.readObject();
          System.out.print(sb);
          sb=(StringBuffer)ois.readObject();
          System.out.println(" "+sb);
}I expect to get the output "foo bar" but getting "foo foo". For every object type it is true that the non-modified object is received, if the same but modified object is sent twice. Is this a bug?

Answer 1

burghard.britzke wrote:
The substitution of writeObject(obj) with writeUnshared(obj) on the client and readObject(obj) with readUnshared(obj) lead to the "foo foo", too.I always use reset() on the OOS.
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
            ObjectOutputStream oos = new ObjectOutputStream(baos);
            StringBuffer sb = new StringBuffer("foo");
            oos.reset();
            oos.writeObject(sb);
            sb.replace(0, sb.length(), "bar");
            oos.reset();
            oos.writeObject(sb);
            oos.close();
            ObjectInputStream ois = new ObjectInputStream(new ByteArrayInputStream(baos.toByteArray()));
            StringBuffer sb = (StringBuffer) ois.readObject();
            System.out.print(sb);
            sb = (StringBuffer) ois.readObject();
            System.out.println(" " + sb);
        }