【环境问题】消灭红叉-The superclass javax.servlet.http.HttpServlet was not found on the Java Build Path

环境：
Windows 7 旗舰版
jdk7
Spring Tool Suite（STS，version：3.6.0.RELEASE）

经常使用Eclipse（STS）作为发开IDE的，经常会碰到项目莫名奇妙的红叉
1. index.jsp 红叉：The superclass javax.servlet.http.HttpServlet was not found on the Java Build Path
…未完待续

详细说明：
1. index.jsp红叉

解决办法
右击“项目名称”-》Properties—》Java Build Path-》Libraries-》Add Library…-》Server Runtime-》Apache Tomcat v[6|7|8].0

参考：

java错误：The superclass “javax.servlet.http.HttpServlet” was not found on the Java Bu

JavaWeb:报错信息The superclass “javax.servlet.http.HttpServlet” was not found on the Java Build Path

项目忽然出现 The superclass “javax.servlet.http.HttpServlet” was not found on the Java Build Path 解决方法

Eclipse 中 XML 警告 No grammar constraints (DTD or XML Schema) 解决方法