/**
* Sets the <code>SocketImplFactory</code>. This may be done only once per virtual machine.
* Subsequent attempts will generate a <code>SocketException</code>. Note that a <code>
* SecurityManager</code> check is made prior to setting the factory. If insufficient privileges
* exist to set the factory, then an <code>IOException</code> will be thrown.
*
* @exception SecurityException If the <code>SecurityManager</code> does not allow this operation.
* @exception SocketException If the SocketImplFactory is already defined
* @exception IOException If any other error occurs
*/
public static synchronized void setSocketImplFactory(SocketImplFactory fac) throws IOException {
// See if already set
if (factory != null) throw new SocketException("SocketImplFactory already defined");
// Check permissions
SecurityManager sm = System.getSecurityManager();
if (sm != null) sm.checkSetFactory();
if (fac == null) throw new SocketException("SocketImplFactory cannot be null");
factory = fac;
}