Java Tip 40: Object transport via datagram packets

Transport Java objects over the network with datagram packets

By Shengxi Zhou, JavaWorld.com, 10/01/97

The presence of these new classes in Java 1.1 makes it possible to transmit a running object over the network. To do this, the object, along with those objects that have been referenced, must be serializable -- that is, able to be converted into a byte stream. Fortunately, in Java 1.1, most built-in classes are serializable. Some classes, however, are not (class Object is a prime example). Not to worry. If your class is derived from a non-serializable class, serialization can be achieved by using method defaultWriteObject() in the ObjectOutputStream class, and can then be deserialized by method defaultReadObject() in class ObjectInputStream.

Once serialized, the object is ready to transmitted over a network. The following example demonstrates how to make an object serializable and how to send it through a stream socket:

//Object Output
import java.net.*;
import java.io.*;
//The sample class to be sent: Factory
class Factory implements Serializable
{  private void writeObject(ObjectOutputStream out) throws IOException  
{    out.defaultWriteObject();  }
  private void readObject(ObjectInputStream in)
               throws IOException, ClassNotFoundException  
{    in.defaultReadObject();  }
}
public class ShowObjOutput
{  public static void main(String[] arg)  
{    try    
{      ObjectOutputStream os;
      Socket sock = new Socket("panda.cs.uno.edu", 6000);
 //panda is the host name
      Factory fa = new Factory();
      os = new ObjectOutputStream( new
             BufferedOutputStream(sock.getOutputStream()));
      os.writeObject(fa);
    }
    catch (IOException ex)
    {}
  }
}

This next example shows you how an object is received by ObjectInputStream from a stream socket:

//Object Input
import java.net.*;
import java.io.*;
public class ShowObjInput
{  public static void main(String[] arg)
  {    try    
{      ObjectInputStream is;
      ServerSocket servSock = new ServerSocket(6000);
      Sock sock;
      sock = servSock.accept();
      is = new ObjectInputStream( new
               BufferedInputStream(sock.getInputStream()));
      Factory o = (Factory)is.readObject();
    }    catch (IOException ex)
    {}
  }
}

Besides tightly coupled sockets, Java also supports connectionless datagram communication with the DatagramSocket class. Can we achieve object input/output with datagram communication? Accomplishing this is not as straightforward as with stream sockets. The problem is that the DatagramSocket is not attached to any stream; rather, a DatagramSocket takes a byte array as parameter for sending and receiving.

Free Download - 5 Minute Product Review. When slow equals Off: Manage the complexity of Web applications - Symphoniq

Free Download - 5 Minute Product Review. Realize the benefits of real user monitoring in less than an hour. - Symphoniq