一、錯誤示例

最近在寫socket程式時，偶然發現程式被卡住很長時間，除錯後發現是建立Socket時，採用的方式不對：

Socket s = new Socket(String host, String port);

當採用該方式建立Socket時，預設的連結超時時間為0（A timeout of zero is interpreted as an infinite timeout. The connection will then block until established or an error occurs.），也就意味著連結永不超時，直到發生連結超時異常，所以程式會被卡住，並最終丟擲異常。

二、正確示例

若要設定連結超時，需要使用如下方式建立Socket：

Socket s = new Socket();
SocketAddress socketAddress = new InetSocketAddress(serverIp, port);
s.connect(socketAddress, timeout);

其中timeout就是設定的超時時間，當超時時間到時會丟擲SocketTimeoutException而不會無限等待的去嘗試連結。

附

設定從Socket讀取資料超時

通過Socket方法setSoTimeout(int timeout)，Javadoc關於該方法的的說明如下：

Enable/disable SO_TIMEOUT with the specified timeout, in milliseconds. 

With this option set to a non-zero timeout, a read() call on the InputStream associated with this Socket will block for only this amount of time.

If the timeout expires, a java.net.SocketTimeoutException is raised, though the
 
 Socket is still valid. 

The option must be enabled prior to entering the blocking operation to have effect. 

The timeout must be > 0. A timeout of zero is interpreted as an infinite timeout.