在多线程环境下，使用 httpclient.xxx.jar包的 new DefaultHttpClient() ； 构造函数创建的client客户端将会引发以下这个错误：

Invalid use of SingleClientConnManager: connection still allocated.

Make sure to release the connection before allocating another one.

java.lang.IllegalStateException: Invalid use of SingleClientConnManager: connection still allocated.

Make sure to release the connection before allocating another one.

解决办法：

使用 new DefaultHttpClient(new ThreadSafeClientConnManager()); 构造一个client客户端即可解决该问题