如何判断socket已断开连接

2个参考：

http://www.blogjava.net/amplifier/archive/2007/04/12/110131.html

http://cuisuqiang.iteye.com/blog/1453632

大致方法是使用socket.sendUrgentData(0xFF); // 发送心跳包

try{ 
socket.sendUrgentData(0xFF); 
}catch(Exception ex){ 
reconnect(); 
}