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

The superclass "javax.servlet.http.HttpServlet" was not found on the Java Build Path是由于没有导入相关的java支持包的缘故 

出错截图在：

解决方案如下：选择项目右键-->Build Path-->Configure Build Path--> add Libray-->Server Runtime-->Next-->选择Tomcat -->Finish()