几点：

1）输入结束循环的条件不正确：

1) incorrect conditions for end of input loop:

while (inputMessage.equals("QUIT")); // Server#processConnection 

while (outputMessage.equals("QUIT")) // Client#processConnection 

这些应该被否定（！）。

these should be negated ("!").

2）你应该开始 System.in 阅读主题：

2) you should start you System.in reading threads:

new Thread() { // instead of `Runnable`
   ...
}.start();

3）你应该在服务器上断开监听循环，例如 EOFException ，表示客户端已断开连接。

3) you should break listening loop on server for some exceptions, like EOFException which means that client was disconnected.