感谢 ChDw(米) , zedk928(其实我是一个卧底!) 的回复
sock.getSendBufferSize()出来是8k应该没问题,我现在在看是不是:
BufferedOutputStream out = new BufferedOutputStream(outputToSocket);的原因
BufferedOutputStream默认的size是512,我打算换成:
BufferedOutputStream out = new BufferedOutputStream(outputToSocket,8192);