Primefaces TreeTable - can't instantiate class

Question

I'm trying to create a treetable from a properties file that i'm parsing and I keep getting the error "Can't instantiate class" with the code below. I'm not sure why it would be throwing this exception where it does.

for(Map.Entry<Object, Object> prop : props.entrySet()) {
    String key = ((String)prop.getKey()).replace("_", " ");
    String value = (String)prop.getValue();

    String[] parts = key.split("\\.");

    if(parts.length > 4) {
        boolean topLevelExists = false;

        // if there are already child nodes
        if(root.getChildCount() > 0) {
            for(TreeNode n : root.getChildren()) {
                System.out.println("n = "+n);
                System.out.println("n.data = "+((Menu)n.getData()).getName());
                System.out.println("n.getType = "+n.getType());

                if(n.getType().equals(parts[2])) {  
                    System.out.println("they equal");
                    topLevelExists = true;
                    if(topLevelExists == true) {
                        System.out.println("topLevelExists");
                        TreeNode node = new DefaultTreeNode(parts[2], new Menu(parts[2], value), n);
                    }
                } else {
                    TreeNode node = new DefaultTreeNode(parts[2], new Menu(parts[2], value), root);  // FAILS ON THIS LINE WITH THE EXCEPTION BELOW
                }
            }
        // else we are creating the first node
        } else {
            TreeNode node = new DefaultTreeNode(parts[2], new Menu(parts[2], value), root);
        }


    }
}

Menu.java

public class Menu {

    private String name;
    private String path;

    public Menu(String name, String path) {
        this.name = name;
        this.path = path;
    }

    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getPath() {
        return path;
    }
    public void setPath(String path) {
        this.path = path;
    }
}

Exception thrown

com.sun.faces.mgbean.ManagedBeanCreationException: Cant instantiate class: edu.mayo.ccs.alliance.menu.backing.MenuBacking.
    at com.sun.faces.mgbean.BeanBuilder.newBeanInstance(BeanBuilder.java:193)
    at com.sun.faces.mgbean.BeanBuilder.build(BeanBuilder.java:102)
    at com.sun.faces.mgbean.BeanManager.createAndPush(BeanManager.java:409)
    at com.sun.faces.mgbean.BeanManager.create(BeanManager.java:269)
    at com.sun.faces.el.ManagedBeanELResolver.resolveBean(ManagedBeanELResolver.java:244)
    at com.sun.faces.el.ManagedBeanELResolver.getValue(ManagedBeanELResolver.java:116)
    at com.sun.faces.el.DemuxCompositeELResolver._getValue(DemuxCompositeELResolver.java:176)
    at com.sun.faces.el.DemuxCompositeELResolver.getValue(DemuxCompositeELResolver.java:203)
    at org.apache.el.parser.AstIdentifier.getValue(AstIdentifier.java:69)
    at org.apache.el.parser.AstValue.getValue(AstValue.java:112)
    at org.apache.el.ValueExpressionImpl.getValue(ValueExpressionImpl.java:186)
    at com.sun.faces.facelets.el.TagValueExpression.getValue(TagValueExpression.java:109)
    at javax.faces.component.ComponentStateHelper.eval(ComponentStateHelper.java:193)
    at org.primefaces.component.api.UITree.getValue(UITree.java:99)
    at org.primefaces.component.treetable.TreeTableRenderer.encodeTbody(TreeTableRenderer.java:260)
    at org.primefaces.component.treetable.TreeTableRenderer.encodeRegularMarkup(TreeTableRenderer.java:208)
    at org.primefaces.component.treetable.TreeTableRenderer.encodeMarkup(TreeTableRenderer.java:132)
    at org.primefaces.component.treetable.TreeTableRenderer.encodeEnd(TreeTableRenderer.java:88)
    at javax.faces.component.UIComponentBase.encodeEnd(UIComponentBase.java:884)
    at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1681)
    at javax.faces.render.Renderer.encodeChildren(Renderer.java:168)
    at javax.faces.component.UIComponentBase.encodeChildren(UIComponentBase.java:854)
    at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1674)
    at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1677)
    at org.primefaces.component.accordionpanel.AccordionPanelRenderer.encodeTab(AccordionPanelRenderer.java:218)
    at org.primefaces.component.accordionpanel.AccordionPanelRenderer.encodeTabs(AccordionPanelRenderer.java:147)
    at org.primefaces.component.accordionpanel.AccordionPanelRenderer.encodeMarkup(AccordionPanelRenderer.java:91)
    at org.primefaces.component.accordionpanel.AccordionPanelRenderer.encodeEnd(AccordionPanelRenderer.java:71)
    at javax.faces.component.UIComponentBase.encodeEnd(UIComponentBase.java:884)
    at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1681)
    at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1677)
    at org.primefaces.component.tabview.TabViewRenderer.encodeTabContent(TabViewRenderer.java:279)
    at org.primefaces.component.tabview.TabViewRenderer.encodeContents(TabViewRenderer.java:237)
    at org.primefaces.component.tabview.TabViewRenderer.encodeMarkup(TabViewRenderer.java:128)
    at org.primefaces.component.tabview.TabViewRenderer.encodeEnd(TabViewRenderer.java:69)
    at javax.faces.component.UIComponentBase.encodeEnd(UIComponentBase.java:884)
    at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1681)
    at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1677)
    at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1677)
    at com.sun.faces.application.view.FaceletViewHandlingStrategy.renderView(FaceletViewHandlingStrategy.java:399)
    at com.sun.faces.application.view.MultiViewHandler.renderView(MultiViewHandler.java:131)
    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:509)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.primefaces.webapp.filter.FileUploadFilter.doFilter(FileUploadFilter.java:79)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at edu.mayo.ccs.alliance.util.BrowserNotSupportedFilter.doFilter(BrowserNotSupportedFilter.java:151)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:563)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
    at edu.mayo.ccs.ctsu.sso.CustomAuthenticator.invoke(CustomAuthenticator.java:42)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:293)
    at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:859)
    at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:602)
    at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)
    at java.lang.Thread.run(Thread.java:662)
Caused by: java.util.ConcurrentModificationException
    at java.util.AbstractList$Itr.checkForComodification(AbstractList.java:372)
    at java.util.AbstractList$Itr.next(AbstractList.java:343)
    at edu.mayo.ccs.alliance.menu.backing.MenuBacking.parseMenu(MenuBacking.java:151)
    at edu.mayo.ccs.alliance.menu.backing.MenuBacking.<init>(MenuBacking.java:96)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
    at java.lang.Class.newInstance0(Class.java:355)
    at java.lang.Class.newInstance(Class.java:308)
    at com.sun.faces.mgbean.BeanBuilder.newBeanInstance(BeanBuilder.java:188)
    ... 64 more

Answer 1

To the point, you're modifying root while you're still iterating over it.

for (TreeNode n : root.getChildren()) {
    // ...
    TreeNode node = new DefaultTreeNode(parts[2], new Menu(parts[2], value), root);  // FAILS ON THIS LINE WITH THE EXCEPTION BELOW
    // ...
}

The new DefaultTreeNode will add the new Menu as a child of the given root. However, this will cause the iteration to fail, because the backing collection has concurrently been modified. This is all what the ConcurrentModificationException is trying to tell you.

You need to rewrite the code accordingly so that the new DefaultTreeMode child for root is not been created while you're iterating over the root. I can see basically 2 ways to solve this: redesign the code so that you don't need to loop over the root at all, or collect the new children in some List or Map and add them afterwards to the root. The concrete functional requirement is not exactly clear, so I can't suggest which one would be the right solution.