Sockets are different than datagrams because they use a connection-based paradigm to transmit data. This means that both a sender and a receiver must be running and establish a communication channel for data to be exchanged. To use a real-world analogy, a socket connection is like calling a friend on the telephone. If the friend does not answer, a conversation cannot take place. Datagrams on the other hand are more like sending a letter to a friend, where a note is placed into an envelope, addressed, and mailed.

The following code demonstrates how to set up a listener to monitor a port for an inbound socket connection.

try
{
  ServerSocketConnection ssc = (ServerSocketConnection) 
  Connector.open("socket://:9002");
  StreamConnection sc = null;
  InputStream is = null;
  try{
    sc = ssc.acceptAndOpen();
    is = sc.openInputStream();
    int ch = 0;
    StringBuffer sb = new StringBuffer();
    while ((ch = is.read()) != -1){
      sb.append((char)ch);
    }
    System.out.println(sb.toString());
  } finally{
      ssc.close();
      sc.close();
      is.close();
  }
} catch (IOException x) {
    x.printStackTrace();
}

In this example a ServerSocketConnection is opened on port 9002. This type of connection is used for sole purpose of listening for an inbound socket connection. The code goes into a wait state when the acceptAndOpen() method is called. When a socket connection is established, the acceptAndOpen() method returns with an instance of a SocketConnection. Opening an input stream on this connection allows data to be read from the transmission.

The next example demonstrates the code required by the client to initiate the socket connection.

try{
  SocketConnection sc = (SocketConnection) 
    Connector.open("socket://localhost:9002");
  OutputStream os = null;
  try{
    os = sc.openOutputStream();
    byte[] data = "Hello from a socket!".getBytes();
    os.write(data);
  } finally{
      sc.close();
      os.close();
  }
} catch (IOException x){
	x.printStackTrace();
}

In this example a SocketConnection is established on port 9002 of the local machine. When using sockets, this is the point on the server side that the acceptAndOpen() method returns. If the connection is successfully opened, the OutputStream is obtained and a message is written to the stream. Note that because sockets are connection based, if there is no server listening for an incoming socket connection an exception will be thrown.

2008-08-01

Comments(8)

1.	not satisfied friend. for Socket class it asks to import java.net in J2ME By: Gaurav at 2009-01-28 07:34:42
2.	Hi Gaurav, The sample in this tutorial is just a code snippet (NOT THE COMPLETE MIDLET). Therefore you should import the required packages when you add this snippet into your midlet. By: Ramlak at 2009-01-28 20:00:08
3.	How make comunication between client and server, sending mensage between them ?????? By: alex at 2009-01-30 07:12:49
4.	pls give me code for exact communication between client and server By: SIRAJ at 2009-02-19 06:24:10
5.	Thanks friend this code will really help me i will used it in my own client server program thanks once again By: Anonymous at 2009-05-04 20:16:58
6.	plz can u give me code for key excange b/n pda & apache server. By: visnas at 2009-05-04 20:18:32
7.	i am developing a video streaming pc server to j2me client system that the j2me player can playing video from pc server using wifi please any one tell me the study material for the above project if some code is availabe for video streaming then send to my email address ziaullah126@gmail.com thanks in advance i am waiting for expert help By: ziathegreat at 2009-05-19 13:19:15
8.	pls can any one have any idea about storing the call, means :when the sender press the button call and start speak it must be recorded in the buffer of mobile and the receiver listen to the call from the memory . how can i do it in j2me By: souhir at 2010-01-30 11:04:48

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