为什么java.util.Scanner.next（）返回空字符串？

I have a device which implements a Telnet server and I am writing java code to communicate with it. The current implementation "works" and by that I mean it will for a while then hangs, sometimes immediately, sometimes after an hour or anywhere in between. I am not ruling out the possibility that it is the device itself, however, long running sessions with putty seem to have no trouble, so I am working under the assumption that it is my java code.I have a device which implements a Telnet serve