AppletTalk.com Java discussions newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  LinkedList NullPointerException occurs after switched from I          AppletTalk.com Forum Index -> ibm.software.java.linux View previous topic :: View next topic   Author Message Tohru Kao Guest Posted: Mon Jul 07, 2003 5:56 pm    Post subject: LinkedList NullPointerException occurs after switched from I Hi, I encounter a NullPointerException after I switched from IBM JVM 1.4.0 to IBM JVM 1.4.1. The component I use is: Linux 7.3 IBM JVM 1.4.1 freemarker 1.5.2 tomcat 4.1.18 Please give any advice about this NullPointerException which I didn't encounter in IBM JVM 1.4.0. Here is the stack trace: java.lang.NullPointerException at java.util.LinkedList$ListItr.next(LinkedList.java:510) at freemarker.template.expression.ExpressionBuilder.associateOperators(ExpressionBuilder.java) at freemarker.template.expression.ExpressionBuilder.buildExpression(ExpressionBuilder.java) at freemarker.template.expression.ExpressionBuilder.build(ExpressionBuilder.java) at freemarker.template.compiler.StandardTemplateParser.parseExpression(StandardTemplateParser.java) at freemarker.template.compiler.StandardTemplateParser.parseVariable(StandardTemplateParser.java) at freemarker.template.compiler.StandardTemplateParser.parseVariableInstruction(StandardTemplateParser.java) at freemarker.template.compiler.StandardTemplateParser.getNextInstruction(StandardTemplateParser.java) at freemarker.template.compiler.LinkedListTemplateBuilder.buildLinks(LinkedListTemplateBuilder.java) at freemarker.template.compiler.LinkedListTemplateBuilder.buildGenericBody(LinkedListTemplateBuilder.java) at freemarker.template.compiler.LinkedListTemplateBuilder.buildStatement(LinkedListTemplateBuilder.java) at freemarker.template.instruction.GenericStartInstruction.callBuilder(GenericStartInstruction.java) at freemarker.template.compiler.LinkedListTemplateBuilder.buildLinks(LinkedListTemplateBuilder.java) at freemarker.template.compiler.LinkedListTemplateBuilder.buildStatement(LinkedListTemplateBuilder.java) at freemarker.template.instruction.IfInstruction.callBuilder(IfInstruction.java) at freemarker.template.compiler.LinkedListTemplateBuilder.buildLinks(LinkedListTemplateBuilder.java) at freemarker.template.compiler.LinkedListTemplateBuilder.build(LinkedListTemplateBuilder.java) at freemarker.template.Template.compileText(Template.java) at freemarker.template.Template.compileFromStream(Template.java) at freemarker.template.Template.compileFromStream(Template.java) at freemarker.template.Template.compileFromFile(Template.java) at freemarker.template.Template.(Template.java) at freemarker.template.FileTemplateCache.loadTemplate(FileTemplateCache.java) at freemarker.template.FileTemplateCache.getLatestTemplate(FileTemplateCache.java) at freemarker.template.FileTemplateCache.getTemplate(FileTemplateCache.java) at org.mytest.HtmlTemplateController.getTemplate(HtmlTemplateController.java:73) at org.mytest.HtmlTemplateController.getTemplate(HtmlTemplateController.java:99) at org.mytest.MyServlet.doGet(MyServlet.java:101) at javax.servlet.http.HttpServlet.service(HttpServlet.java:740) at javax.servlet.http.HttpServlet.service(HttpServlet.java:853) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:247) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:193) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:260) at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:643) at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:480) at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:995) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191) at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:643) at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:480) at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:995) at org.apache.catalina.core.StandardContext.invoke(StandardContext.java:2415) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:180) at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:643) at org.apache.catalina.valves.ErrorDispatcherValve.invoke(ErrorDispatcherValve.java:170) at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:641) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:172) at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:641) at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:480) at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:995) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:174) at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:643) at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:480) at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:995) at org.apache.coyote.tomcat4.CoyoteAdapter.service(CoyoteAdapter.java:223) at org.apache.jk.server.JkCoyoteHandler.invoke(JkCoyoteHandler.java:261) at org.apache.jk.common.HandlerRequest.invoke(HandlerRequest.java:360) at org.apache.jk.common.ChannelSocket.invoke(ChannelSocket.java:632) at org.apache.jk.common.ChannelSocket.processConnection(ChannelSocket.java:590) at org.apache.jk.common.SocketConnection.runIt(ChannelSocket.java:707) at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:530) at java.lang.Thread.run(Thread.java:568) TIA -Tohru Back to top Roedy Green Guest Posted: Sat Jul 12, 2003 5:56 pm    Post subject: Re: LinkedList NullPointerException occurs after switched fr On Mon, 07 Jul 2003 10:56:48 -0700, Tohru Kao <jacoder (AT) yahoo (DOT) com> wrote or quoted : Quote: at java.util.LinkedList$ListItr.next(LinkedList.java:510) possibly one implementation filters out null elements from a LinkedList and other preserves them?? -- Canadian Mind Products, Roedy Green. Coaching, problem solving, economical contract programming. See http://mindprod.com/jgloss/jgloss.html for The Java Glossary. Back to top xarax Guest Posted: Sat Jul 12, 2003 10:49 pm    Post subject: Re: LinkedList NullPointerException occurs after switched fr Tohru Kao <jacoder (AT) yahoo (DOT) com> wrote Quote: Hi, I encounter a NullPointerException after I switched from IBM JVM 1.4.0 to IBM JVM 1.4.1. The component I use is: Linux 7.3 IBM JVM 1.4.1 freemarker 1.5.2 tomcat 4.1.18 Please give any advice about this NullPointerException which I didn't encounter in IBM JVM 1.4.0. Here is the stack trace: java.lang.NullPointerException at java.util.LinkedList$ListItr.next(LinkedList.java:510) /snip/ You'll have to look at the source for LinkedList.java near line 510 to see what it's trying to do. Most likely, it is advancing to its next pointer and getting a null value. The list is probably corrupted by a concurrent modification by another thread. Iteration doesn't guarantee that it will detect all such modifications. The LinkedList implementation is not synchronized. Thus, I suspect that the application that is using the LinkedList is broken, rather than the LinkedList implementation. Back to top Neil Masson Guest Posted: Mon Jul 14, 2003 8:12 am    Post subject: Re: LinkedList NullPointerException occurs after switched fr xarax wrote: Quote: Tohru Kao <jacoder (AT) yahoo (DOT) com> wrote in message news:<7qcjgv4oagp3ushf57c4gd5r991dbratcj (AT) 4ax (DOT) com>... Hi, I encounter a NullPointerException after I switched from IBM JVM 1.4.0 to IBM JVM 1.4.1. The component I use is: Linux 7.3 IBM JVM 1.4.1 freemarker 1.5.2 tomcat 4.1.18 Please give any advice about this NullPointerException which I didn't encounter in IBM JVM 1.4.0. Here is the stack trace: java.lang.NullPointerException at java.util.LinkedList$ListItr.next(LinkedList.java:510) /snip/ You'll have to look at the source for LinkedList.java near line 510 to see what it's trying to do. Most likely, it is advancing to its next pointer and getting a null value. The list is probably corrupted by a concurrent modification by another thread. Iteration doesn't guarantee that it will detect all such modifications. The LinkedList implementation is not synchronized. Thus, I suspect that the application that is using the LinkedList is broken, rather than the LinkedList implementation. This analysis is spot on. What has changed in 1.4.1 is that the next and prev pointers of a removed list element are set to null. So perhaps one thread is removing an object from a list, while another is iterating through the list. You might have got away with this before, but now a NullPointerException will be thrown. 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