java.net.SocketException: Connection reset

求大佬们帮助，跟老师一样的代码，为什么会出现这个错误啊

java.net.SocketException: Connection reset
 at java.net.SocketInputStream.read(SocketInputStream.java:210)
 at java.net.SocketInputStream.read(SocketInputStream.java:141)
 at sun.nio.cs.StreamDecoder.readBytes(StreamDecoder.java:284)
 at sun.nio.cs.StreamDecoder.implRead(StreamDecoder.java:326)
 at sun.nio.cs.StreamDecoder.read(StreamDecoder.java:178)
 at java.io.InputStreamReader.read(InputStreamReader.java:184)
 at java.io.BufferedReader.fill(BufferedReader.java:161)
 at java.io.BufferedReader.readLine(BufferedReader.java:324)
 at java.io.BufferedReader.readLine(BufferedReader.java:389)
 at Server.main(Server.java:27)