Dynamic Web Module facet version问题

The default superclass, "javax.servlet.http.HttpServlet", according to the project's Dynamic Web Module facet version (3.1), was not found on the Java Build Path.

1.右键项目

2.点击Properties

3.点击Java Build Path，右边找到Libraries，下面点击JRE System Library，右边点击Edit，将JRE改为自己的