Question

I am developing a Tree component, which might be prunned according to the user input. I have all nodes cached, in order to provide primefaces component model with always the same instances of the tree nodes.

But the problem is, that when I change the parent-child relationships (remove some of them), I always get a concurrent modification exception… Is there any way to workaround this issue or am I missing something.

Thanks in advance.

/**
 * Recursively copy the hierarchy and prune not visible branches
 * @param originalNode node of the original hierarchy to be copied
 * @param parent parent node in the new hierarchy
 * @param visibleNodes set of nodes, which should be included in the new hierarchy
 * @param model model of the TreeAutompleteComponent
 * @return copy of the oroginal node in the new hierarchy
 */
private TreeNode copyHierarchy(TreeNode originalNode, TreeNode parent, Set<TreeNode> visibleNodes, TreeAutocompleteModel model) {
    if (!visibleNodes.contains(originalNode)) {
        return null;
    }

    TreeNode newNode = model.getCompleteModelNodes().get(((NodeWrapper)originalNode.getData()).getIri());//new DefaultTreeNode(originalNode.getData(), parent);
    for (int i = 0; i < originalNode.getChildCount(); i++) {
        copyHierarchy((TreeNode) originalNode.getChildren().get(i), newNode, visibleNodes, model);
    }
    newNode.setParent(parent); //when removed, no exception occurs
    return newNode;
}

The exception

ava.util.ConcurrentModificationException
    at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:819)
    at java.util.ArrayList$Itr.next(ArrayList.java:791)
    at org.primefaces.component.tree.TreeRenderer.encodeTreeNodeChildren(TreeRenderer.java:284)
    at org.primefaces.component.tree.TreeRenderer.encodeTreeNode(TreeRenderer.java:274)
    at org.primefaces.component.tree.TreeRenderer.encodeMarkup(TreeRenderer.java:165)
    at org.primefaces.component.tree.TreeRenderer.encodeEnd(TreeRenderer.java:96)
    at javax.faces.component.UIComponentBase.encodeEnd(UIComponentBase.java:875)
    at com.sun.faces.renderkit.html_basic.HtmlBasicRenderer.encodeRecursive(HtmlBasicRenderer.java:312)
    at com.sun.faces.renderkit.html_basic.GroupRenderer.encodeChildren(GroupRenderer.java:105)
    at javax.faces.component.UIComponentBase.encodeChildren(UIComponentBase.java:845)
    at com.sun.faces.renderkit.html_basic.HtmlBasicRenderer.encodeRecursive(HtmlBasicRenderer.java:304)
    at com.sun.faces.renderkit.html_basic.GridRenderer.renderRow(GridRenderer.java:185)
    at com.sun.faces.renderkit.html_basic.GridRenderer.encodeChildren(GridRenderer.java:129)
    at javax.faces.component.UIComponentBase.encodeChildren(UIComponentBase.java:845)
    at com.sun.faces.renderkit.html_basic.HtmlBasicRenderer.encodeRecursive(HtmlBasicRenderer.java:304)
    at com.sun.faces.renderkit.html_basic.GridRenderer.renderRow(GridRenderer.java:185)
    at com.sun.faces.renderkit.html_basic.GridRenderer.encodeChildren(GridRenderer.java:129)
    at javax.faces.component.UIComponentBase.encodeChildren(UIComponentBase.java:845)
    at com.sun.faces.renderkit.html_basic.HtmlBasicRenderer.encodeRecursive(HtmlBasicRenderer.java:304)
    at com.sun.faces.renderkit.html_basic.GroupRenderer.encodeChildren(GroupRenderer.java:105)
    at javax.faces.component.UIComponentBase.encodeChildren(UIComponentBase.java:845)
    at com.sun.faces.renderkit.html_basic.HtmlBasicRenderer.encodeRecursive(HtmlBasicRenderer.java:304)
    at com.sun.faces.renderkit.html_basic.GroupRenderer.encodeChildren(GroupRenderer.java:105)
    at javax.faces.component.UIComponentBase.encodeChildren(UIComponentBase.java:845)
    at com.sun.faces.renderkit.html_basic.HtmlBasicRenderer.encodeRecursive(HtmlBasicRenderer.java:304)
    at com.sun.faces.renderkit.html_basic.GroupRenderer.encodeChildren(GroupRenderer.java:105)
    at javax.faces.component.UIComponentBase.encodeChildren(UIComponentBase.java:845)
    at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1779)
    at com.sun.faces.renderkit.html_basic.CompositeRenderer.encodeChildren(CompositeRenderer.java:78)
    at javax.faces.component.UIComponentBase.encodeChildren(UIComponentBase.java:845)
    at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1779)
    at javax.faces.render.Renderer.encodeChildren(Renderer.java:168)
    at javax.faces.component.UIComponentBase.encodeChildren(UIComponentBase.java:845)
    at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1779)
    at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1782)
    at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1782)
    at com.sun.faces.application.view.FaceletViewHandlingStrategy.renderView(FaceletViewHandlingStrategy.java:424)
    at com.sun.faces.application.view.MultiViewHandler.renderView(MultiViewHandler.java:125)
    at com.sun.faces.lifecycle.RenderResponsePhase.execute(RenderResponsePhase.java:121)
    at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101)
    at com.sun.faces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:139)
    at javax.faces.webapp.FacesServlet.service(FacesServlet.java:594)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:304)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.netbeans.modules.web.monitor.server.MonitorFilter.doFilter(MonitorFilter.java:393)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:240)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:164)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:462)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:164)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:100)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:563)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:399)
    at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:317)
    at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:204)
    at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:182)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:311)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
    at java.lang.Thread.run(Thread.java:722)

Answer 1

This is solution, that works. I havent localized the actual issue, but I have sucessfully workaround all it…

public TreeNode constructActualModel(TreeAutocompleteMatcherIface matcher) {
    if (prunedModel == null) {
        eraseHierarchyStructure();
        prunedModel = copyHierarchy((TreeNode) completeModel, getVisibleNodes(matcher));
    }
    return prunedModel;
}

/**
 * Recursively copy the hierarchy and prune not visible branches
 * @param originalNode node of the original hierarchy to be copied
 * @param visibleNodes set of nodes, which should be included in the new hierarchy
 * @param model model of the TreeAutompleteComponent
 * @return copy of the oroginal node in the new hierarchy
 */
private TreeNode copyHierarchy(TreeNode originalNode, Set<TreeNode> visibleNodes) {
    if (!visibleNodes.contains(originalNode)) {
        return null;
    }

    TreeNode newNode = this.getCompleteModelNodes().get(((NodeWrapper) originalNode.getData()).getIri());//new DefaultTreeNode(originalNode.getData(), parent);
    List<TreeNode> children = new ArrayList<TreeNode>();
    for (int i = 0; i < originalNode.getChildCount(); i++) {
        TreeNode child = copyHierarchy((TreeNode) originalNode.getChildren().get(i), visibleNodes);
        if(child != null){
            children.add(child);
        }
    }
    ((DefaultTreeNode) newNode).setChildren(children);
    return newNode;
}

private void eraseHierarchyStructure() {
    for (TreeNode node : duplicateCompleteModelNodes.values()) {
        node.setParent(null);
    }       
}

It was necessary to do it the opposite way – to get the impl to be able to call the setChildren method and at first erase the hierarchy…