在MyEclipse中写一个JSP页面出现的问题

at ytl.ServerThread.run(ServerThread.java:18)
==========ServerThread============
java.lang.NullPointerException
at ytl.ServerThread.run(ServerThread.java:18)
==========ServerThread============
java.lang.NullPointerException
at ytl.ServerThread.run(ServerThread.java:18)
==========ServerThread============
java.lang.NullPointerException
at ytl.ServerThread.run(ServerThread.java:18)
==========ServerThread============
java.lang.NullPointerException
at ytl.ServerThread.run(ServerThread.java:18)
==========ServerThread============
java.lang.NullPointerException
at ytl.ServerThread.run(ServerThread.java:18)
==========ServerThread============
java.lang.NullPointerException
at ytl.ServerThread.run(ServerThread.java:18)
==========ServerThread============
java.lang.NullPointerException
at ytl.ServerThread.run(ServerThread.java:18)
==========ServerThread============
java.lang.NullPointerException
at ytl.ServerThread.run(ServerThread.java:18)
在console下面会出现这种异常，不能在8080窗口打开tomcat？

空指针异常。。。在Servlet层是不是有对象没有被实例化啊？

是不是少了getter和setter方法，或是页面没有传有效值