Checked There are two solutions, most of the Internet is the first case
1, servlet version and imported project web using the IDE tomcat inconsistent; tomcat version using the servlet See web.xml tomcat installation directory of the file, the file header has clearly stated, for example, it is used in FIG servlet 3.0
2, for an unknown reason, the solution is as follows
Click the project list in the upper inverted triangle icon = "Filters and Customization =" Content tab and uncheck WEB option, as shown below:
Point "OK", the problem is solved