The superclass "javax.servlet.http.HttpServlet" was not found on the Java Build Path 解决方案

The superclass “javax.servlet.http.HttpServlet” was not found on the Java Build Path错误

建项目出现上面的问题，解决方法：
项目右击–>属性或Build Path–>Java Build Path–>Libraries–>Add Libray…–>Server Runtime –>Apache Tomcat v7.0

参考：https://www.cnblogs.com/pszw/p/3677530.html 点我
目前不知道一劳永逸的方法，如有大佬还请指教