Server-Side Java - Java - page 645

Opening a Server Socket for Business

Problem

You need to write a socket-based server.

Solution

Create a ServerSocket for the given port number.

Discussion

The ServerSocket represents the “other end” of a connection, the server that waits patiently
for clients to come along and connect to it. You construct a ServerSocket with just the port
number. [ 49 ] Because it doesn't need to connect to another host, it doesn't need a particular
host's address as the client socket constructor does.

Assuming the ServerSocket constructor doesn't throw an exception, you're in business.
Your next step is to await client activity, which you do by calling accept() . This call blocks
until a client connects to your server; at that point, the accept() returns to you a Socket ob-
ject (not a ServerSocket ) that is connected in both directions to the Socket object on the
client (or its equivalent, if written in another language). Example 16-1 shows the code for a
socket-based server.

Example 16-1. Listen.java
public public class Listen {

/** The TCP port for the service. */
public

class Listen

public static static final final short short PORT = 9999 ;

public public static static void void main ( String [] argv ) throws throws IOException {

ServerSocket sock ;
Socket clientSock ;
try try {

sock = new new ServerSocket ( PORT );

while while (( clientSock = sock . accept ()) != null null ) {

// Process it.
process ( clientSock );

}