java - servlet在tomcat运行时报错

Question

servlet在tomcat运行时报错，错误及代码如图，新手求高手指点！不胜感激！

Answer 1

The author should learn to debug by interrupting by himself.

username 客户端有传这个值吗？这个是我猜的。
楼主看一下 LogLet 22行的代码吧，有一个变量是 null.

Answer 2

1. Check whether the Servlet configuration in web.xml is correct;
2. Check whether the parameter name in the request URL is username;