Java Web报错：The superclass "javax.servlet.http.HttpServlet" was not found on the Java Build Path

Multiple annotations found at this line:

The superclass "javax.servlet.http.HttpServlet" was not found on the Java BuIld Path

The import java.util cannot be resolved

原因：
原来Javaweb工程类中没有添加 Tomcat运行时相关类 导致。

想添加却没有Apache Tomcat，需要在Build Path->Config Build Path中添加

右击 web工程 --> 属性或Build Path --> Config Build Path... --> Java Build Path --> Libraries --> Add Library... --> MyEclipse Server Library --> Apache Tomcat v9.0

Java Web报错：The superclass "javax.servlet.http.HttpServlet" was not found on the Java Build Path

错误提示消失了