2014-8-14 13:43:43 org.apache.catalina.core.StandardWrapperValve invoke
严重: Servlet.service() for servlet [action] in context with path [] threw exception [java.lang.NullPointerException] with root cause
java.lang.NullPointerException
at org.quickupstart.struts.action.LoginValidateAction.execute(LoginValidateAction.java:33)
at org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:431)
at org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:236)
at org.apache.struts.action.ActionServlet.process(ActionServlet.java:1196)
at org.apache.struts.action.ActionServlet.doGet(ActionServlet.java:414)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:620)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
at org.quickupstart.common.EncodingFileter.doFilter(EncodingFileter.java:43)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:220)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:501)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:950)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1070)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:611)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:314)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Unknown Source)
应用在本地跑没有一点问题，部署到服务器，一触发功能后台就抛这个异常，但是前台也没有报HTTP 500错误，功能运行正常。
异常里说的33行报红指针，代码如下:
[code="java"]
HttpSession session = request.getSession(false);
String validate_code = session.getAttribute("code").toString();//这个是33行
[/code]
用log4j也可以输出值。已经晕了！抓狂中........................
服务器是不是集群了，没有做session复制？用session做存储其实很不可取，建议用缓存技术替代session。
两种情况。
1.获取到的session对象为空。
request.getSession(false);如果当前有session则返回当前session，否则返回null;
request.getSession();如果当前有session则返回当前session，否则返回一个新的session。
2.session不为空，session.getAttribute("code")后返回的为空;
用断点调试就知道了，另外，凡是设计到session的地方，最好是用aop模式进行方法前校验。
为什么用HttpSession session = request.getSession(false);而不是HttpSession session = request.getSession();呢 ？或者HttpSession session = request.getSession(true);呢
String validate_code = session.getAttribute("code").toString();//这个是33行
这样String validate_code = (String)session.getAttribute("code");
这样session中code为null的时候也正常。
空指针的问题是最好查的了。。。