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我正在使用Netbeans。運行從會話bean調用方法的servlet時，出現以下異常。爲什麼servlet拋出這個Servlet.service（）異常？
ApplicationDispatcher[/TheLibrarySystem-war] PWC1231: Servlet.service() for servlet ListReservations threw exception
java.lang.NullPointerException
at org.apache.jsp.ListReservations_jsp._jspService(ListReservations_jsp.java from :68)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:109)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:847)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:389)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:486)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:380)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:847)
at org.apache.catalina.core.ApplicationFilterChain.servletService(ApplicationFilterChain.java:427)
at org.apache.catalina.core.ApplicationDispatcher.doInvoke(ApplicationDispatcher.java:873)
at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:723)
at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:558)
at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:456)
at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:382)
at servlet.TheLibrarySystemServlet.processRequest(TheLibrarySystemServlet.java:86)
at servlet.TheLibrarySystemServlet.doGet(TheLibrarySystemServlet.java:185)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:734)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:847)
at org.apache.catalina.core.ApplicationFilterChain.servletService(ApplicationFilterChain.java:427)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:315)
at org.apache.catalina.core.StandardContextValve.invokeInternal(StandardContextValve.java:287)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:218)
at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:648)
at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:593)
at com.sun.enterprise.web.WebPipeline.invoke(WebPipeline.java:94)
at com.sun.enterprise.web.PESessionLockingStandardPipeline.invoke(PESessionLockingStandardPipeline.java:98)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:222)
at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:648)
at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:593)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:587)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:1093)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:166)
at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:648)
at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:593)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:587)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:1093)
at org.apache.coyote.tomcat5.CoyoteAdapter.service(CoyoteAdapter.java:291)
at com.sun.enterprise.web.connector.grizzly.DefaultProcessorTask.invokeAdapter(DefaultProcessorTask.java:666)
at com.sun.enterprise.web.connector.grizzly.DefaultProcessorTask.doProcess(DefaultProcessorTask.java:597)
at com.sun.enterprise.web.connector.grizzly.DefaultProcessorTask.process(DefaultProcessorTask.java:872)
at com.sun.enterprise.web.connector.grizzly.DefaultReadTask.executeProcessorTask(DefaultReadTask.java:341)
at com.sun.enterprise.web.connector.grizzly.DefaultReadTask.doTask(DefaultReadTask.java:263)
at com.sun.enterprise.web.connector.grizzly.DefaultReadTask.doTask(DefaultReadTask.java:214)
at com.sun.enterprise.web.connector.grizzly.TaskBase.run(TaskBase.java:264)
at com.sun.enterprise.web.connector.grizzly.ssl.SSLWorkerThread.run(SSLWorkerThread.java:106)
PWC1412: WebModule[/TheLibrarySystem-war] ServletContext.log():TheLibrarySystemServlet: Exception in TheLibrarySystemServlet.processRequest()
會話bean中的方法肯定工作正常，並將正確的值返回給servlet端。代碼崩潰： dispatcher.forward（request，response）;代碼崩潰： dispatcher.forward（request，response）;
谷歌搜索，它似乎不是一個代碼問題，任何想法是什麼原因導致它，以及如何解決？