在做javaWeb项目时，我们经常会出现丢失包的情况，如下图所示的错误，我们应该怎么解决呢？
根据网上教程向工程中加入tomcat的servlet-api.jar和jsp-api.jar的包
此时项目确实不会报错了，但是更坑的报错出现了；运行项目发现
严重: Servlet.service() for servlet jsp threw exception
java.lang.NullPointerException
at org.apache.jsp.index_jsp._jspInit(index_jsp.java:23)
at org.apache.jasper.runtime.HttpJspBase.init(HttpJspBase.java:52)
at org.apache.jasper.servlet.JspServletWrapper.getServlet(JspServletWrapper.java:164)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:340)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:313)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:260)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:723)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:88)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:76)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:293)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:861)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:620)
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)
at java.lang.Thread.run(Thread.java:745)
然后百度一顿搜索；查找到的原因是jsp-api.jar包与tomcat下的jsp-api.jar包冲突，要移除冲突的包；然后就去找WEB-INF下面的包，没发现这两个包啊，确实是很奇怪；
后面认真查看项目的结构，问题终于找到了；发现少了 JAVA EE5 Libraries系统包；而servlet-api.jar和jsp-api.jar在JAVA EE5 Libraries包下，直接使用javaee5 library的包即可；
解决方法
引入 JAVA EE5 Libraries系统包，并查找.classpath文件中查看是否有servlet-api.jar和jsp-api.jar这两个包的加载配置，如果有的话就删除即可
最重要的一点 一定要clean下项目，不然不起作用。