暑假自学，用servlet+jsp+java bean写了一个博客，在本地Tomcat里面跑的时候没有问题，部署到SAE后，能进入到应用首页，但是当请求servlet的时候报http 500错误，错误代码如下
HTTP ERROR 500
Problem accessing /servlet/ShowArticle. Reason:
Server Error
Caused by:
java.lang.NullPointerException
at com.tj.servlet.ShowArticle.doGet(ShowArticle.java:32)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:707)
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$CachedChain.doFilter(ServletHandler.java:1357)
at com.sina.sae.facade.SaeFilterChain.doFilter(SaeFilterChain.java:28)
at com.tj.filter.CharacterEncoding.doFilter(CharacterEncoding.java:32)
at com.sina.sae.servlet.SaeServletHandler.servletHandlerDoFilter(SaeServletHandler.java:56)
at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1328)
at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:476)
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.handler.ContextHandlerCollection.handle(ContextHandlerCollection.java:259)
at org.eclipse.jetty.server.handler.HandlerCollection.handle(HandlerCollection.java:149)
at com.sina.sae.handler.SaeUserInfoHandler.handle(SaeUserInfoHandler.java:105)
at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:110)
at org.eclipse.jetty.rewrite.handler.RewriteHandler.handle(RewriteHandler.java:305)
at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:110)
at org.eclipse.jetty.server.Server.handle(Server.java:346)
at org.eclipse.jetty.server.HttpConnection.handleRequest(HttpConnection.java:589)
at org.eclipse.jetty.server.HttpConnection$RequestHandler.headerComplete(HttpConnection.java:1048)
at org.eclipse.jetty.http.HttpParser.parseNext(HttpParser.java:601)
at org.eclipse.jetty.http.HttpParser.parseAvailable(HttpParser.java:214)
at org.eclipse.jetty.server.HttpConnection.handle(HttpConnection.java:411)
at org.eclipse.jetty.io.nio.SelectChannelEndPoint.handle(SelectChannelEndPoint.java:535)
at org.eclipse.jetty.io.nio.SelectChannelEndPoint$1.run(SelectChannelEndPoint.java:40)
at org.eclipse.jetty.util.thread.QueuedThreadPool$3.run(QueuedThreadPool.java:529)
at java.lang.Thread.run(Thread.java:714)
我的思路是，通过servlet/ShowArticle连接数据库，取出记录，然后把每条记录封装成Java bean对象，再把对象放进List里面，最后存到session里面，然后response.sendRedirect()到articls.jsp页面，在articles.jsp里面通过session.getAttribute()获取list对象，进行操作，最终显示数据。
（图servlet/ShowArticle代码）
整个过程在本地Tomcat里面跑没有出现问题，但是到部署sae上就出现了上面的问题。
新手小白刚刚接触Java web开发，弄了很久没有找到解决办法，跪求各路大神解答。