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  1. ,
    via javacodegeeks.com by Unknown author

    Causes : The Collection is internally modified, while a thread is iterating over it. OR after the creation of an iterator, the Collection is internally modified by any method other than the iterator’s own methods for removal and addition.

  2. ,
    via oracle.com by Unknown author

    In order to avoid more than one threads accessing or modifying the same object, you can synchronize them over the object, in order to allow only one thread to manipulate it over time.

Solutions on the web

via struts-issues by Lukasz Lenart (JIRA), 1 year ago
via struts-issues by ASF subversion and git services (JIRA), 1 year ago
via struts-issues by ASF subversion and git services (JIRA), 1 year ago
via struts-issues by ASF subversion and git services (JIRA), 1 year ago
via struts-issues by ASF subversion and git services (JIRA), 1 year ago
via struts-issues by ASF GitHub Bot (JIRA), 1 year ago
java.util.ConcurrentModificationException: 	at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:901)	at java.util.ArrayList$Itr.next(ArrayList.java:851)	at org.apache.struts2.components.IteratorComponent.end(IteratorComponent.java:333)	at org.apache.struts2.views.freemarker.tags.CallbackWriter.afterBody(CallbackWriter.java:84)	at freemarker.core.Environment.visitAndTransform(Environment.java:427)	at freemarker.core.UnifiedCall.accept(UnifiedCall.java:107)	at freemarker.core.Environment.visit(Environment.java:324)	at freemarker.core.MixedContent.accept(MixedContent.java:54)	at freemarker.core.Environment.visitByHiddingParent(Environment.java:345)	at freemarker.core.IfBlock.accept(IfBlock.java:48)	at freemarker.core.Environment.visit(Environment.java:324)	at freemarker.core.MixedContent.accept(MixedContent.java:54)	at freemarker.core.Environment.visit(Environment.java:324)	at freemarker.core.Environment.process(Environment.java:302)	at freemarker.template.Template.process(Template.java:325)	at org.apache.struts2.components.template.FreemarkerTemplateEngine.renderTemplate(FreemarkerTemplateEngine.java:158)	at org.apache.struts2.components.UIBean.mergeTemplate(UIBean.java:584)	at org.apache.struts2.components.UIBean.end(UIBean.java:538)	at org.apache.struts2.components.UIBean.end(UIBean.java:540)	at org.apache.struts2.views.freemarker.tags.CallbackWriter.afterBody(CallbackWriter.java:84)	at freemarker.core.Environment.visitAndTransform(Environment.java:427)	at freemarker.core.UnifiedCall.accept(UnifiedCall.java:107)	at freemarker.core.Environment.visit(Environment.java:324)	at freemarker.core.MixedContent.accept(MixedContent.java:54)	at freemarker.core.Environment.visitByHiddingParent(Environment.java:345)	at freemarker.core.IfBlock.accept(IfBlock.java:48)	at freemarker.core.Environment.visitByHiddingParent(Environment.java:345)	at freemarker.core.ConditionalBlock.accept(ConditionalBlock.java:48)	at freemarker.core.Environment.visit(Environment.java:324)	at freemarker.core.MixedContent.accept(MixedContent.java:54)	at freemarker.core.Environment.visit(Environment.java:324)	at freemarker.core.Macro$Context.runMacro(Macro.java:184)	at freemarker.core.Environment.invoke(Environment.java:701)	at freemarker.core.UnifiedCall.accept(UnifiedCall.java:84)	at freemarker.core.Environment.visitByHiddingParent(Environment.java:345)	at freemarker.core.IteratorBlock$IterationContext.executeNestedBlockInner(IteratorBlock.java:240)	at freemarker.core.IteratorBlock$IterationContext.executeNestedBlock(IteratorBlock.java:220)	at freemarker.core.IteratorBlock$IterationContext.accept(IteratorBlock.java:194)	at freemarker.core.Environment.visitIteratorBlock(Environment.java:572)	at freemarker.core.IteratorBlock.acceptWithResult(IteratorBlock.java:78)	at freemarker.core.IteratorBlock.accept(IteratorBlock.java:64)	at freemarker.core.Environment.visit(Environment.java:324)	at freemarker.core.MixedContent.accept(MixedContent.java:54)	at freemarker.core.Environment.visit(Environment.java:324)	at freemarker.core.EscapeBlock.accept(EscapeBlock.java:48)	at freemarker.core.Environment.visit(Environment.java:324)	at freemarker.core.MixedContent.accept(MixedContent.java:54)	at freemarker.core.Environment.visit(Environment.java:324)	at freemarker.core.Environment.process(Environment.java:302)	at freemarker.template.Template.process(Template.java:325)	at org.apache.struts2.views.freemarker.FreemarkerResult.doExecute(FreemarkerResult.java:223)	at org.apache.struts2.dispatcher.StrutsResultSupport.execute(StrutsResultSupport.java:191)	at com.opensymphony.xwork2.DefaultActionInvocation.executeResult(DefaultActionInvocation.java:369)	at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:273)	at com.opensymphony.xwork2.interceptor.DefaultWorkflowInterceptor.doIntercept(DefaultWorkflowInterceptor.java:167)	at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)	at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)	at com.opensymphony.xwork2.validator.ValidationInterceptor.doIntercept(ValidationInterceptor.java:265)	at org.apache.struts2.interceptor.validation.AnnotationValidationInterceptor.doIntercept(AnnotationValidationInterceptor.java:76)	at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)	at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)	at com.opensymphony.xwork2.interceptor.ConversionErrorInterceptor.intercept(ConversionErrorInterceptor.java:138)	at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)	at com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:229)	at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)	at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)	at com.opensymphony.xwork2.interceptor.StaticParametersInterceptor.intercept(StaticParametersInterceptor.java:191)	at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)	at com.opensymphony.xwork2.interceptor.PrepareInterceptor.doIntercept(PrepareInterceptor.java:171)	at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)	at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)	at org.apache.struts2.interceptor.ServletConfigInterceptor.intercept(ServletConfigInterceptor.java:164)	at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)	at com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:229)	at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)	at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)	at com.opensymphony.xwork2.interceptor.StaticParametersInterceptor.intercept(StaticParametersInterceptor.java:191)	at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)	at org.apache.struts2.interceptor.MultiselectInterceptor.intercept(MultiselectInterceptor.java:73)	at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)	at org.apache.struts2.interceptor.CheckboxInterceptor.intercept(CheckboxInterceptor.java:91)	at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)	at com.opensymphony.xwork2.interceptor.I18nInterceptor.intercept(I18nInterceptor.java:139)	at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)	at org.apache.struts2.interceptor.MessageStoreInterceptor.intercept(MessageStoreInterceptor.java:197)	at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)	at org.tdar.struts.interceptor.HttpMethodInterceptor.intercept(HttpMethodInterceptor.java:29)	at org.tdar.struts.interceptor.HttpsInterceptor.doHttpIntercept(HttpsInterceptor.java:52)	at org.tdar.struts.interceptor.HttpsInterceptor.intercept(HttpsInterceptor.java:34)	at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)	at org.tdar.struts.interceptor.CacheControlInterceptor.intercept(CacheControlInterceptor.java:40)	at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)	at org.tdar.struts.interceptor.SessionSecurityInterceptor.intercept(SessionSecurityInterceptor.java:85)	at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)	at org.tdar.struts.interceptor.ActivityLoggingInterceptor.intercept(ActivityLoggingInterceptor.java:69)	at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)	at com.opensymphony.xwork2.interceptor.ExceptionMappingInterceptor.intercept(ExceptionMappingInterceptor.java:189)	at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)	at org.apache.struts2.impl.StrutsActionProxy.execute(StrutsActionProxy.java:54)	at org.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:564)	at org.apache.struts2.dispatcher.ng.ExecuteOperations.executeAction(ExecuteOperations.java:81)	at org.apache.struts2.dispatcher.ng.filter.StrutsExecuteFilter.doFilter(StrutsExecuteFilter.java:93)	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)	at com.opensymphony.sitemesh.webapp.SiteMeshFilter.obtainContent(SiteMeshFilter.java:129)	at com.opensymphony.sitemesh.webapp.SiteMeshFilter.doFilter(SiteMeshFilter.java:77)	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)	at org.apache.struts2.dispatcher.ng.filter.StrutsPrepareFilter.doFilter(StrutsPrepareFilter.java:91)	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)	at org.springframework.orm.hibernate4.support.OpenSessionInViewFilter.doFilterInternal(OpenSessionInViewFilter.java:151)	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)	at org.tuckey.web.filters.urlrewrite.RuleChain.handleRewrite(RuleChain.java:176)	at org.tuckey.web.filters.urlrewrite.RuleChain.doRules(RuleChain.java:145)	at org.tuckey.web.filters.urlrewrite.UrlRewriter.processRequest(UrlRewriter.java:92)	at org.tuckey.web.filters.urlrewrite.UrlRewriteFilter.doFilter(UrlRewriteFilter.java:389)	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)	at org.apache.logging.log4j.web.Log4jServletFilter.doFilter(Log4jServletFilter.java:71)	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:170)	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:98)	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)	at org.apache.coyote.ajp.AjpProcessor.process(AjpProcessor.java:193)	at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:607)	at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:313)	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)	at java.lang.Thread.run(Thread.java:745)