jsf - java.util.ConcurrentModificationException with c:forEach to loop and f:ajax to add items to ArrayList -


yes, question concurrentmodificationexception.

my problem:

  • i loopping through arraylist using <c:foreach>
  • i adding value arraylist ajax call
  • i getting java.util.concurrentmodificationexception.

here block of xhtml:

<h:form id="frmquestion" styleclass="form-horizontal">      <h:panelgroup layout="block" id="foreachanswer">         <div>             <c:foreach items="#{questionbean.question.answers}" var="answer" varstatus="loopanswer">                 ...             </c:foreach>         </div>          <h:commandlink immediate="true" styleclass="list-group-item list-group-item-success text-center" action="#{questionbean.addanswer}">             <f:ajax execute="@all"                     render="frmquestion:foreachanswer"                      onevent="ajaxanswer" />             <i class="fa fa-plus"></i> adicionar pergunta         </h:commandlink>     </h:panelgroup>  </h:form>

the @managedbean:

@managedbean     @sessionscoped     public class questionbean {          private question question = new question();          public questionbean() {         }          public void addanswer() {             this.question.addanswer();         }          ...     }

the question class:

@entity     @table     public class question implements serializable {          @id         @sequencegenerator(name="question_pk_sequence", sequencename="seq_rs_question")         @generatedvalue(strategy=generationtype.auto, generator="question_pk_sequence")         private int qst_id;          private int qst_type;          @onetomany         private list<answer> answers = new arraylist<>();          public void addanswer() {             if (this.answers == null) {                 this.answers = new arraylist<>();             }             answer p = new answer();             p.setorder(this.answers.size()+1);             if (this.qst_type == 1 || this.qst_type == 2) {                 p.settype(qst_type);             }             this.answers.add(p); //this raises exception         }          ...     }

i searched solutions none of answers found facing problems <c:foreach>. code working before , don't know did messed all. looked code , didn't see other place answers list navigated.

is possible <c:foreach> keeps looping through collection when ajax called? if is, why?

the best solution found change question.answers arraylist copyonwritearraylist, can't because use collections.sort(answers); in part of question class , throws exception when using copyonwritearraylist.

i accepting solutions make collections.sort() work copyonwritearraylist too, don't have experience java (as it's obvious because think asking noob question).

edit:

stack trace:

java.util.concurrentmodificationexception @ java.util.arraylist$itr.checkforcomodification(unknown source) @ java.util.arraylist$itr.next(unknown source) @ com.sun.faces.facelets.tag.jstl.core.foreachhandler.apply(foreachhandler.java:193) @ javax.faces.view.facelets.compositefacelethandler.apply(compositefacelethandler.java:95) @ javax.faces.view.facelets.delegatingmetataghandler.applynexthandler(delegatingmetataghandler.java:137) @ com.sun.faces.facelets.tag.jsf.componenttaghandlerdelegateimpl.apply(componenttaghandlerdelegateimpl.java:190) @ javax.faces.view.facelets.delegatingmetataghandler.apply(delegatingmetataghandler.java:120) @ javax.faces.view.facelets.compositefacelethandler.apply(compositefacelethandler.java:95) @ javax.faces.view.facelets.delegatingmetataghandler.applynexthandler(delegatingmetataghandler.java:137) @ com.sun.faces.facelets.tag.jsf.componenttaghandlerdelegateimpl.apply(componenttaghandlerdelegateimpl.java:190) @ javax.faces.view.facelets.delegatingmetataghandler.apply(delegatingmetataghandler.java:120) @ com.sun.faces.facelets.tag.jsf.core.viewhandler.apply(viewhandler.java:212) @ javax.faces.view.facelets.compositefacelethandler.apply(compositefacelethandler.java:95) @ com.sun.faces.facelets.tag.ui.definehandler.applydefinition(definehandler.java:106) @ com.sun.faces.facelets.tag.ui.compositionhandler.apply(compositionhandler.java:201) @ com.sun.faces.facelets.impl.defaultfaceletcontext$templatemanager.apply(defaultfaceletcontext.java:395) @ com.sun.faces.facelets.impl.defaultfaceletcontext.includedefinition(defaultfaceletcontext.java:366) @ com.sun.faces.facelets.tag.ui.inserthandler.apply(inserthandler.java:111) @ javax.faces.view.facelets.compositefacelethandler.apply(compositefacelethandler.java:95) @ javax.faces.view.facelets.delegatingmetataghandler.applynexthandler(delegatingmetataghandler.java:137) @ com.sun.faces.facelets.tag.jsf.componenttaghandlerdelegateimpl.apply(componenttaghandlerdelegateimpl.java:190) @ javax.faces.view.facelets.delegatingmetataghandler.apply(delegatingmetataghandler.java:120) @ javax.faces.view.facelets.compositefacelethandler.apply(compositefacelethandler.java:95) @ com.sun.faces.facelets.compiler.namespacehandler.apply(namespacehandler.java:93) @ com.sun.faces.facelets.compiler.encodinghandler.apply(encodinghandler.java:87) @ com.sun.faces.facelets.impl.defaultfacelet.include(defaultfacelet.java:312) @ com.sun.faces.facelets.impl.defaultfacelet.include(defaultfacelet.java:371) @ com.sun.faces.facelets.impl.defaultfacelet.include(defaultfacelet.java:350) @ com.sun.faces.facelets.impl.defaultfaceletcontext.includefacelet(defaultfaceletcontext.java:199) @ com.sun.faces.facelets.tag.ui.compositionhandler.apply(compositionhandler.java:169) @ com.sun.faces.facelets.compiler.namespacehandler.apply(namespacehandler.java:93) @ com.sun.faces.facelets.compiler.encodinghandler.apply(encodinghandler.java:87) @ com.sun.faces.facelets.impl.defaultfacelet.apply(defaultfacelet.java:161) @ com.sun.faces.application.view.faceletviewhandlingstrategy.buildview(faceletviewhandlingstrategy.java:972) @ com.sun.faces.lifecycle.renderresponsephase.execute(renderresponsephase.java:99) @ com.sun.faces.lifecycle.phase.dophase(phase.java:101) @ com.sun.faces.lifecycle.lifecycleimpl.render(lifecycleimpl.java:219) @ javax.faces.webapp.facesservlet.service(facesservlet.java:647) @ org.apache.catalina.core.standardwrapper.service(standardwrapper.java:1682) @ org.apache.catalina.core.standardwrappervalve.invoke(standardwrappervalve.java:318) @ org.apache.catalina.core.standardcontextvalve.invoke(standardcontextvalve.java:160) @ org.apache.catalina.core.standardpipeline.doinvoke(standardpipeline.java:734) @ org.apache.catalina.core.standardpipeline.invoke(standardpipeline.java:673) @ com.sun.enterprise.web.webpipeline.invoke(webpipeline.java:99) @ org.apache.catalina.core.standardhostvalve.invoke(standardhostvalve.java:174) @ org.apache.catalina.connector.coyoteadapter.doservice(coyoteadapter.java:357) @ org.apache.catalina.connector.coyoteadapter.service(coyoteadapter.java:260) @ com.sun.enterprise.v3.services.impl.containermapper.service(containermapper.java:188) @ org.glassfish.grizzly.http.server.httphandler.runservice(httphandler.java:191) @ org.glassfish.grizzly.http.server.httphandler.dohandle(httphandler.java:168) @ org.glassfish.grizzly.http.server.httpserverfilter.handleread(httpserverfilter.java:189) @ org.glassfish.grizzly.filterchain.executorresolver$9.execute(executorresolver.java:119) @ org.glassfish.grizzly.filterchain.defaultfilterchain.executefilter(defaultfilterchain.java:288) @ org.glassfish.grizzly.filterchain.defaultfilterchain.executechainpart(defaultfilterchain.java:206) @ org.glassfish.grizzly.filterchain.defaultfilterchain.execute(defaultfilterchain.java:136) @ org.glassfish.grizzly.filterchain.defaultfilterchain.process(defaultfilterchain.java:114) @ org.glassfish.grizzly.processorexecutor.execute(processorexecutor.java:77) @ org.glassfish.grizzly.nio.transport.tcpniotransport.fireioevent(tcpniotransport.java:838) @ org.glassfish.grizzly.strategies.abstractiostrategy.fireioevent(abstractiostrategy.java:113) @ org.glassfish.grizzly.strategies.workerthreadiostrategy.run0(workerthreadiostrategy.java:115) @ org.glassfish.grizzly.strategies.workerthreadiostrategy.access$100(workerthreadiostrategy.java:55) @ org.glassfish.grizzly.strategies.workerthreadiostrategy$workerthreadrunnable.run(workerthreadiostrategy.java:135) @ org.glassfish.grizzly.threadpool.abstractthreadpool$worker.dowork(abstractthreadpool.java:564) @ org.glassfish.grizzly.threadpool.abstractthreadpool$worker.run(abstractthreadpool.java:544) @ java.lang.thread.run(unknown source)

thanks in advance.


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