Java Web应用部署在SAE平台上出现“java.lang.NullPointerException”错误的原因之一

Java Web应用部署在SAE平台上测试时出现以下错误：

HTTP ERROR 500

Problem accessing /. Reason:

Server Error

Caused by:

java.lang.NullPointerException

at org.apache.jsp.index_jsp._jspService(org.apache.jsp.index_jsp:101)

at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:109)

at javax.servlet.http.HttpServlet.service(HttpServlet.java:820)

at com.sina.sae.jasper.servlet.SaeJspServletWrapper.service(SaeJspServletWrapper.java:225)

at com.sina.sae.jasper.servlet.SaeJspServlet.serviceJspFile(SaeJspServlet.java:238)

at com.sina.sae.jasper.servlet.SaeJspServlet.service(SaeJspServlet.java:187)

at javax.servlet.http.HttpServlet.service(HttpServlet.java:820)

at org.eclipse.jetty.servlet.ServletHolder.handle(ServletHolder.java:538)

at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:478)

at com.sina.sae.servlet.SaeServletHandler.doHandle(SaeServletHandler.java:49)

at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:119)

at org.eclipse.jetty.security.SecurityHandler.handle(SecurityHandler.java:517)

at org.eclipse.jetty.server.session.SessionHandler.doHandle(SessionHandler.java:225)

at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:937)

at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:406)

at org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:183)

at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:871)

at com.sina.sae.webapp.SaeWebAppContext.doScope(SaeWebAppContext.java:166)

at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:117)

at org.eclipse.jetty.server.Dispatcher.forward(Dispatcher.java:284)

at org.eclipse.jetty.server.Dispatcher.forward(Dispatcher.java:115)

at com.sina.sae.facade.SaeRequestDispatcher.forward(SaeRequestDispatcher.java:27)

at org.eclipse.jetty.servlet.DefaultServlet.doGet(DefaultServlet.java:552)

at org.eclipse.jetty.servlet.DefaultServlet.doPost(DefaultServlet.java:592)

at javax.servlet.http.HttpServlet.service(HttpServlet.java:727)

at javax.servlet.http.HttpServlet.service(HttpServlet.java:820)

at org.eclipse.jetty.servlet.ServletHolder.handle(ServletHolder.java:538)

at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:478)

原因之一是Java Web应用引用了额外的servlet_api.jar这与SAE平台的Servlet包产生冲突，如果是这种情况，删除servlet_api.jar包，具体操作时注意将项目里的.classpath文件里的引用路径给删除，对于其他的引用要使用相对路径。