关于 Socket 设置 setSoTimeout 误用的说明

作网络开发的想必对setSoTimeout这个方法很熟悉，知道是设置的超时事件。可是不少人都认为这个是设置链路的超时时间，可是查看相关文档的此方法的说明：

HttpConnectionParams：

Sets the default socket timeout (SO_TIMEOUT) in milliseconds which is the timeout for waiting for data. 
A timeout value of zero is interpreted as an infinite timeout. This value is used when no socket timeout is set in the method parameters.

Socket：

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.

DatagramSocket：

Enable/disable SO_TIMEOUT with the specified timeout, in milliseconds. With this option set to a non-zero timeout, 
a call to receive() for this DatagramSocket will block for only this amount of time. If the timeout expires, a java.net.SocketTimeoutException is raised, 
though the DatagramSocket 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.

看文档的详细说明，很显然，这种理解是不对的，不是连接的超时时间。 简单归纳起来，应该是：读取数据时阻塞链路的超时时间。

上面Socket的setSoTimeout的文档翻译后的内容为：

setSoTimeout  
public void setSoTimeout(int timeout)  
    throws SocketException启用/禁用带有指定超时值的 SO_TIMEOUT，以毫秒为单位。将此选项设为非零的超时值时，在与此 Socket 关联的 InputStream 上调用 read() 将只阻塞此时间长度。  
    若是超过超时值，将引起 java.net.SocketTimeoutException，虽然 Socket 仍旧有效。选项必须在进入阻塞操做前被启用才能生效。  
    超时值必须是 > 0 的数。超时值为 0 被解释为无穷大超时值。   
参数：  
timeout - 指定的以毫秒为单位的超时值。   
抛出：   
SocketException - 若是底层协议出现错误，例如 TCP 错误。  

最简单的测试验证的方法是：

写一个基于Socket的下载方法，设置setSoTimeout后，下载一个大文件，会发现，下载的时间超过setSoTimeout的值以后，就会失败！！