The SO_TIMEOUT option sets a timer on all I/O methods of a socket that block so that you don't have to wait forever if they don't return. This works for operations such as accept( ) on server sockets and read( ) or write( ) on all sockets. If the timer expires before the operation would complete, an InterruptedIOException is thrown. You can catch the exception and continue to use the socket normally if it is appropriate, or you can take the opportunity to bail out of the operation. Multithreaded, blocking servers, such as TinyHttpd, can use this sort of technique for their shutdown logic: 

 serverSocket.setSoTimeout( 2000 ); // 2 seconds
 while ( !shutdown ) {
 try {
 Socket client = serverSocket.accept( );
 handleClient( client );
 } catch ( InterruptedIOException e ) {
 // ignore the exception
 }
 // exit
 }


You set the timer by calling the setSoTimeout( ) method of the Socket class with the timeout period, in milliseconds, as an int argument. This works for regular Sockets, ServerSockets (TCP), and DatagramSockets (UDP), discussed later in this chapter. To find the current timeout value, call getSoTimeout( ). This feature is a workaround for the fact that stream-oriented I/O operations in Java are blocking, and there is no way to test, or poll, them for activity. Later in this chapter, we'll complete our discussion of the NIO package, which provides full nonblocking I/O for all types of operations, including sockets.