java.util.ConcurrentModificationException与c：forEach to循环和f：ajax将项添加到ArrayList

时间：2015-05-31 22:08:49

标签： ajax jsf foreach jstl concurrentmodification

是的，这是关于ConcurrentModificationException的另一个问题。

我的问题：

  • 我使用<c:forEach>
    • 循环遍历我的ArrayList
  • 我正在使用ajax调用
    • 向ArrayList添加值
  • 我收到了java.util.ConcurrentModificationException。

这是我的xhtml块：

<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>

@ManagedBean：

@ManagedBean    
@SessionScoped    
public class QuestionBean {    

    private Question question = new Question();    

    public QuestionBean() {    
    }    

    public void addAnswer() {    
        this.question.addAnswer();    
    }    

    ...    
}

问题类：

@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 the exception    
    }    

    ...    
}

我搜索了解决方案，但我找到的答案都没有<c:forEach>。这段代码以前工作过，我不知道我做了什么搞砸了。我查看了我的代码，但没有看到导航answers列表的任何其他位置。

调用ajax时，<c:forEach>是否有可能在集合中循环？如果是，为什么？

我找到的最佳解决方案是将Question.answers从ArrayList更改为CopyOnWriteArrayList，但我不能这样做，因为我在另一部分使用Collections.sort(answers);在使用CopyOnWriteArrayList时，问题类会引发另一个异常。

我接受使Collections.sort()与CopyOnWriteArrayList一起使用的解决方案，但我对Java没有太多经验（因为我觉得我在问一个noob问题，因此很明显）。

修改

堆栈追踪：

java.util.ConcurrentModificationException
at java.util.ArrayList$Itr.checkForComodification(Unknown Source)
at java.util.ArrayList$Itr.next(Unknown Source)
at com.sun.faces.facelets.tag.jstl.core.ForEachHandler.apply(ForEachHandler.java:193)
at javax.faces.view.facelets.CompositeFaceletHandler.apply(CompositeFaceletHandler.java:95)
at javax.faces.view.facelets.DelegatingMetaTagHandler.applyNextHandler(DelegatingMetaTagHandler.java:137)
at com.sun.faces.facelets.tag.jsf.ComponentTagHandlerDelegateImpl.apply(ComponentTagHandlerDelegateImpl.java:190)
at javax.faces.view.facelets.DelegatingMetaTagHandler.apply(DelegatingMetaTagHandler.java:120)
at javax.faces.view.facelets.CompositeFaceletHandler.apply(CompositeFaceletHandler.java:95)
at javax.faces.view.facelets.DelegatingMetaTagHandler.applyNextHandler(DelegatingMetaTagHandler.java:137)
at com.sun.faces.facelets.tag.jsf.ComponentTagHandlerDelegateImpl.apply(ComponentTagHandlerDelegateImpl.java:190)
at javax.faces.view.facelets.DelegatingMetaTagHandler.apply(DelegatingMetaTagHandler.java:120)
at com.sun.faces.facelets.tag.jsf.core.ViewHandler.apply(ViewHandler.java:212)
at javax.faces.view.facelets.CompositeFaceletHandler.apply(CompositeFaceletHandler.java:95)
at com.sun.faces.facelets.tag.ui.DefineHandler.applyDefinition(DefineHandler.java:106)
at com.sun.faces.facelets.tag.ui.CompositionHandler.apply(CompositionHandler.java:201)
at com.sun.faces.facelets.impl.DefaultFaceletContext$TemplateManager.apply(DefaultFaceletContext.java:395)
at com.sun.faces.facelets.impl.DefaultFaceletContext.includeDefinition(DefaultFaceletContext.java:366)
at com.sun.faces.facelets.tag.ui.InsertHandler.apply(InsertHandler.java:111)
at javax.faces.view.facelets.CompositeFaceletHandler.apply(CompositeFaceletHandler.java:95)
at javax.faces.view.facelets.DelegatingMetaTagHandler.applyNextHandler(DelegatingMetaTagHandler.java:137)
at com.sun.faces.facelets.tag.jsf.ComponentTagHandlerDelegateImpl.apply(ComponentTagHandlerDelegateImpl.java:190)
at javax.faces.view.facelets.DelegatingMetaTagHandler.apply(DelegatingMetaTagHandler.java:120)
at javax.faces.view.facelets.CompositeFaceletHandler.apply(CompositeFaceletHandler.java:95)
at com.sun.faces.facelets.compiler.NamespaceHandler.apply(NamespaceHandler.java:93)
at com.sun.faces.facelets.compiler.EncodingHandler.apply(EncodingHandler.java:87)
at com.sun.faces.facelets.impl.DefaultFacelet.include(DefaultFacelet.java:312)
at com.sun.faces.facelets.impl.DefaultFacelet.include(DefaultFacelet.java:371)
at com.sun.faces.facelets.impl.DefaultFacelet.include(DefaultFacelet.java:350)
at com.sun.faces.facelets.impl.DefaultFaceletContext.includeFacelet(DefaultFaceletContext.java:199)
at com.sun.faces.facelets.tag.ui.CompositionHandler.apply(CompositionHandler.java:169)
at com.sun.faces.facelets.compiler.NamespaceHandler.apply(NamespaceHandler.java:93)
at com.sun.faces.facelets.compiler.EncodingHandler.apply(EncodingHandler.java:87)
at com.sun.faces.facelets.impl.DefaultFacelet.apply(DefaultFacelet.java:161)
at com.sun.faces.application.view.FaceletViewHandlingStrategy.buildView(FaceletViewHandlingStrategy.java:972)
at com.sun.faces.lifecycle.RenderResponsePhase.execute(RenderResponsePhase.java:99)
at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101)
at com.sun.faces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:219)
at javax.faces.webapp.FacesServlet.service(FacesServlet.java:647)
at org.apache.catalina.core.StandardWrapper.service(StandardWrapper.java:1682)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:318)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:160)
at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:734)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:673)
at com.sun.enterprise.web.WebPipeline.invoke(WebPipeline.java:99)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:174)
at org.apache.catalina.connector.CoyoteAdapter.doService(CoyoteAdapter.java:357)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:260)
at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:188)
at org.glassfish.grizzly.http.server.HttpHandler.runService(HttpHandler.java:191)
at org.glassfish.grizzly.http.server.HttpHandler.doHandle(HttpHandler.java:168)
at org.glassfish.grizzly.http.server.HttpServerFilter.handleRead(HttpServerFilter.java:189)
at org.glassfish.grizzly.filterchain.ExecutorResolver$9.execute(ExecutorResolver.java:119)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeFilter(DefaultFilterChain.java:288)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeChainPart(DefaultFilterChain.java:206)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.execute(DefaultFilterChain.java:136)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.process(DefaultFilterChain.java:114)
at org.glassfish.grizzly.ProcessorExecutor.execute(ProcessorExecutor.java:77)
at org.glassfish.grizzly.nio.transport.TCPNIOTransport.fireIOEvent(TCPNIOTransport.java:838)
at org.glassfish.grizzly.strategies.AbstractIOStrategy.fireIOEvent(AbstractIOStrategy.java:113)
at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.run0(WorkerThreadIOStrategy.java:115)
at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.access$100(WorkerThreadIOStrategy.java:55)
at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy$WorkerThreadRunnable.run(WorkerThreadIOStrategy.java:135)
at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:564)
at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.run(AbstractThreadPool.java:544)
at java.lang.Thread.run(Unknown Source)

提前致谢。

0 个答案:

没有答案
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