The type javax.servlet.http.HttpServletRequest cannot be resolved.

如某个类出现

The type javax.servlet.http.HttpServletRequest cannot be resolved. It is indirectly referenced from 
 required .class files

这个错误，则缺少servetlet的引用库，解决方法如下：

右键工程-->Properties-->Java Build Path--Libraries-->Add External JARs..选择MyEclipse的安装目录如：D:\MyEclipse2014\plugins，找到javax.servlet.jsp_2.2.0.v201112011158.jar，javax.servlet_3.0.0.v201112011016.jar(版本不同，包名可能稍有区别)两个包进行添加即可。