java.lang.NullPointerException
at com.opensymphony.module.sitemesh.taglib.decorator.TitleTag.doEndTag(TitleTag.java:32)
at org.apache.jsp.WEB_002dINF.view.common._404_jsp._jspx_meth_sitemesh_005ftitle_005f0(_404_jsp.java:274)
at org.apache.jsp.WEB_002dINF.view.common._404_jsp._jspService(_404_jsp.java:190)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:443)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:385)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:329)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:230)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165)
at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:715)
at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:462)
at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:385)
at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:311)
at org.apache.catalina.core.StandardHostValve.custom(StandardHostValve.java:395)
at org.apache.catalina.core.StandardHostValve.status(StandardHostValve.java:254)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:177)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:624)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:349)
at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:495)
at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:767)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1347)
at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:745)
at com.opensymphony.module.sitemesh.taglib.decorator.TitleTag.doEndTag(TitleTag.java:32)
标题标签中有变量是null
注意你的堆栈，首先报404了网页不存在，另外都有行号，你可以跟进代码，看看那个对象为null了