java.util.ConcurrentModificationException in JasperReports

Question

We have a web application deployed to Websphere 6.1.0.19 on Windows. We occasionally see this ConcurrentModificationException on a few of our reports. We are using JasperReports 2.0.5 in production. The full stacktrace is following:

java.util.ConcurrentModificationException
      at java.util.AbstractList$Itr.checkForComodification(AbstractList.java:464)
      at java.util.AbstractList$Itr.next(AbstractList.java:435)
      at net.sf.jasperreports.engine.data.JRBeanCollectionDataSource.next(JRBeanCollectionDataSource.java:91)
      at com.advtechgrp.bop.medical.reports.core.implementation.MedicalReportDataSourceImpl.next(MedicalReportDataSourceImpl.java:61)
      at net.sf.jasperreports.engine.fill.JRFillDataset.advanceDataSource(JRFillDataset.java:830)
      at net.sf.jasperreports.engine.fill.JRFillDataset.next(JRFillDataset.java:748)
      at net.sf.jasperreports.engine.fill.JRBaseFiller.next(JRBaseFiller.java:1438)
      at net.sf.jasperreports.engine.fill.JRVerticalFiller.fillReport(JRVerticalFiller.java:111)
      at net.sf.jasperreports.engine.fill.JRBaseFiller.fill(JRBaseFiller.java:895)      at net.sf.jasperreports.engine.fill.JRBaseFiller.fill(JRBaseFiller.java:817)
      at net.sf.jasperreports.engine.fill.JRFiller.fillReport(JRFiller.java:89)
      at net.sf.jasperreports.engine.JasperFillManager.fillReport(JasperFillManager.java:601)
      at com.advtechgrp.bop.medical.reports.core.MedicalReportBase.getReportList(MedicalReportBase.java:160)
      at com.advtechgrp.bop.medical.reports.core.implementation.MedicalReportCreator.createJasperExporter(MedicalReportCreator.java:275)
      at com.advtechgrp.bop.medical.reports.core.implementation.MedicalReportCreator.createExporter(MedicalReportCreator.java:228)
      at com.advtechgrp.bop.medical.reports.core.implementation.MedicalReportCreator.createReportUnsafe(MedicalReportCreator.java:196)
      at com.advtechgrp.bop.medical.reports.core.implementation.MedicalReportCreator.createReport(MedicalReportCreator.java:80)
      at com.advtechgrp.bop.medical.reports.core.web.MedicalReportServlet.doPost(MedicalReportServlet.java:132)
      at javax.servlet.http.HttpServlet.service(HttpServlet.java:763)
      at javax.servlet.http.HttpServlet.service(HttpServlet.java:856)
      at com.ibm.ws.cache.servlet.ServletWrapper.serviceProxied(ServletWrapper.java:282)
      at com.ibm.ws.cache.servlet.CacheHook.handleFragment(CacheHook.java:459)
      at com.ibm.ws.cache.servlet.CacheHook.handleServlet(CacheHook.java:265)
      at com.ibm.ws.cache.servlet.ServletWrapper.service(ServletWrapper.java:262)
      at com.ibm.ws.webcontainer.servlet.ServletWrapper.service(ServletWrapper.java:1075)
      at com.ibm.ws.webcontainer.servlet.ServletWrapper.service(ServletWrapper.java:1016)
      at com.ibm.ws.webcontainer.filter.WebAppFilterChain.doFilter(WebAppFilterChain.java:118)
      at com.ibm.ws.webcontainer.filter.WebAppFilterChain._doFilter(WebAppFilterChain.java:87)
      at com.ibm.ws.webcontainer.filter.WebAppFilterManager.doFilter(WebAppFilterManager.java:771)
      at com.ibm.ws.webcontainer.filter.WebAppFilterManager.doFilter(WebAppFilterManager.java:679)
      at com.ibm.ws.webcontainer.servlet.ServletWrapper.handleRequest(ServletWrapper.java:546)
      at com.ibm.ws.wswebcontainerservlet.ServletWrapper.handleRequest(ServletWrapper.java:478)
      at com.ibmws.webcontainer.webapp.WebAppRequestDispatcher.forward(WebAppRequestDispatcher.java:321)
      at com.advtechgrp.bop.medical.web.filter.UrlRewritingFilter.doFilter(UrlRewritingFilter.java:132)
      at com.ibm.ws.webcontainer.filterFilterInstanceWrapper.doFilter(FilterInstanceWrapper.java:190)
      at com.ibm.ws.webcontainer.filter.WebAppFilterChain.doFilter(WebAppFilterChain.java:130)
      at com.advtechgrp.bop.medical.web.filter.GZIPFilter.doFilter(GZIPFilter.java:36)
      at com.ibm.ws.webcontainer.filter.FilterInstanceWrapper.doFilter(FilterInstanceWrapper.java:190)
      at com.ibm.ws.webcontainer.filter.WebAppFilterChain.doFilter(WebAppFilterChain.java:130)
      at com.advtechgrp.bop.medical.web.filter.WebLogFilter.doFilter(WebLogFilter.java:69)
      at com.ibm.ws.webcontainer.filter.FilterInstanceWrapper.doFilter(FilterInstanceWrapper.java:190)
      at com.ibm.ws.webcontainer.filter.WebAppFilterChain.doFilter(WebAppFilterChain.java:130)
      at com.advtechgrp.bop.medical.web.filter.SecurityFilter.doFilter(SecurityFilter.java:174)
      at com.ibm.ws.webcontainerfilter.FilterInstanceWrapper.doFilter(FilterInstanceWrapper.java:190)
      at com.ibm.ws.webcontainer.filter.WebAppFilterChain.doFilter(WebAppFilterChain.java:130)
      at com.ibm.ws.webcontainer.filter.WebAppFilterChain._doFilter(WebAppFilterChain.java:87)
      at com.ibm.ws.webcontainer.filter.WebAppFilterManager.doFilter(WebAppFilterManager.java:771)
      at com.ibm.ws.webcontainer.filter.WebAppFilterManager.doFilter(WebAppFilterManager.java:679)
      at com.ibm.ws.webcontainer.servlet.ServletWrapper.handleRequest(ServletWrapper.java:546)
      at com.ibm.ws.wswebcontainer.servlet.ServletWrapper.handleRequest(ServletWrapper.java:478)
      at com.ibm.ws.webcontainer.servlet.CacheServletWrapper.handleRequest(CacheServletWrapper.java:90)
      at com.ibm.ws.webcontainer.WebContainer.handleRequest(WebContainer.java:744)
      at com.ibm.ws.wswebcontainer.WebContainer.handleRequest(WebContainer.java:1455)
      at com.ibmws.webcontainer.channel.WCChannelLink.ready(WCChannelLink.java:115)
      at com.ibm.ws.http.channel.inbound.impl.HttpInboundLink.handleDiscrimination(HttpInboundLink.java:458)
      at com.ibm.ws.http.channel.inbound.impl.HttpInboundLink.handleNewInformation(HttpInboundLink.java:387)
      at com.ibm.ws.http.channel.inbound.impl.HttpICLReadCallback.complete(HttpICLReadCallback.java:102)
      at com.ibm.ws.tcp.channel.impl.AioReadCompletionListener.futureCompleted(AioReadCompletionListener.java:165)
      at com.ibm.io.async.AbstractAsyncFuture.invokeCallback(AbstractAsyncFuture.java:217)
      at com.ibm.io.async.AsyncChannelFuture.fireCompletionActions(AsyncChannelFuture.java:161)
      at com.ibm.io.async.AsyncFuture.completed(AsyncFuture.java:136)
      at com.ibm.io.async.ResultHandler.complete(ResultHandler.java:195)
      at com.ibm.io.async.ResultHandler.runEventProcessingLoop(ResultHandler.java:743)
      at com.ibmio.async.ResultHandler$2.run(ResultHandler.java:873)
      at com.ibm.ws.util.ThreadPool$Worker.run(ThreadPool.java:1473)

Thanks,
Tom

Answer 1

Hum... this is a case of concurrent access to something that isn't thread-safe. I can't tell you more until I see the code, or at least a schematic of your software, though.

Answer 2

JasperReports is now on version 3.5, so it may be worth checking whether changes post 2.0.5 (your version) have addressed any threading issues. That obviously won't resolve your current production issue, but a rebuild with the new version might.

Having said all that (and not being familiar with JasperReports) I would suspect client-threaded code.

Answer 3

This is caused by the backing store of the iterator being altered while the iterator is in use. This is not a concurrency problem related to threading, as it is easy enough to do on a single thread as well.

More detailed description on this question

Your biggest problem now will be if it is fixable by you or a bug in the Jasper code.