NPE at TreeTableRenderer.encodeEnd - primefaces

Question

This is my TreeTable definition on xhtml page:
<p:treeTable var="r" value="#{mybean.tree}">
I can see in catalina.out file that every day this happens a few times:
12-Jan-2015 10:13:00.119 SEVERE [ajp-apr-8009-exec-211] com.sun.faces.application.view.FaceletViewHandlingStrategy.handleRenderException Error Rendering View[/my_page.xhtml]
java.lang.NullPointerException
at org.primefaces.component.treetable.TreeTableRenderer.encodeEnd(TreeTableRenderer.java:127)
at javax.faces.component.UIComponentBase.encodeEnd(UIComponentBase.java:919)
at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1863)
at com.sun.faces.context.PartialViewContextImpl$PhaseAwareVisitCallback.visit(PartialViewContextImpl.java:582)
at com.sun.faces.component.visit.PartialVisitContext.invokeVisitCallback(PartialVisitContext.java:183)
at org.primefaces.component.api.UITree.visitTree(UITree.java:648)
at javax.faces.component.UIComponent.visitTree(UIComponent.java:1700)
at javax.faces.component.UIForm.visitTree(UIForm.java:371)
at javax.faces.component.UIComponent.visitTree(UIComponent.java:1700)
at com.sun.faces.context.PartialViewContextImpl.processComponents(PartialViewContextImpl.java:403)
at com.sun.faces.context.PartialViewContextImpl.processPartial(PartialViewContextImpl.java:322)
at org.primefaces.context.PrimePartialViewContext.processPartial(PrimePartialViewContext.java:60)
at javax.faces.component.UIViewRoot.encodeChildren(UIViewRoot.java:1004)
at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1856)
at com.sun.faces.application.view.FaceletViewHandlingStrategy.renderView(FaceletViewHandlingStrategy.java:430)
at com.sun.faces.application.view.MultiViewHandler.renderView(MultiViewHandler.java:133)
at com.sun.faces.lifecycle.RenderResponsePhase.execute(RenderResponsePhase.java:120)
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.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:291)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:219)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:501)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:142)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:610)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:537)
at org.apache.coyote.ajp.AbstractAjpProcessor.process(AbstractAjpProcessor.java:831)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:658)
at org.apache.tomcat.util.net.AprEndpoint$SocketWithOptionsProcessor.run(AprEndpoint.java:2344)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:745)
12-Jan-2015 10:13:00.120 SEVERE [ajp-apr-8009-exec-211] com.sun.faces.context.AjaxExceptionHandlerImpl.handlePartialResponseError java.lang.NullPointerException
at org.primefaces.component.treetable.TreeTableRenderer.encodeEnd(TreeTableRenderer.java:127)
at javax.faces.component.UIComponentBase.encodeEnd(UIComponentBase.java:919)
at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1863)
at com.sun.faces.context.PartialViewContextImpl$PhaseAwareVisitCallback.visit(PartialViewContextImpl.java:582)
at com.sun.faces.component.visit.PartialVisitContext.invokeVisitCallback(PartialVisitContext.java:183)
at org.primefaces.component.api.UITree.visitTree(UITree.java:648)
at javax.faces.component.UIComponent.visitTree(UIComponent.java:1700)
at javax.faces.component.UIForm.visitTree(UIForm.java:371)
at javax.faces.component.UIComponent.visitTree(UIComponent.java:1700)
at com.sun.faces.context.PartialViewContextImpl.processComponents(PartialViewContextImpl.java:403)
at com.sun.faces.context.PartialViewContextImpl.processPartial(PartialViewContextImpl.java:322)
at org.primefaces.context.PrimePartialViewContext.processPartial(PrimePartialViewContext.java:60)
at javax.faces.component.UIViewRoot.encodeChildren(UIViewRoot.java:1004)
at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1856)
at com.sun.faces.application.view.FaceletViewHandlingStrategy.renderView(FaceletViewHandlingStrategy.java:430)
at com.sun.faces.application.view.MultiViewHandler.renderView(MultiViewHandler.java:133)
at com.sun.faces.lifecycle.RenderResponsePhase.execute(RenderResponsePhase.java:120)
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.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:291)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:219)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:501)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:142)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:610)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:537)
at org.apache.coyote.ajp.AbstractAjpProcessor.process(AbstractAjpProcessor.java:831)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:658)
at org.apache.tomcat.util.net.AprEndpoint$SocketWithOptionsProcessor.run(AprEndpoint.java:2344)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:745)
I haven't gottten any user complaints and am not sure yet what the user is doing when this happens. I was assuming she is just opening the page but because of handlePartialResponseError I guess it could be also expanding/collapsing.
Does the error indicate that my object is null in one entry of the tree? In my code I have made sure no nulls are added so this should not be the case.
mybean is a #SessionScoped #ManagedBean (used to be #ViewScoped but now the tree is cached for each user).
My setup is:
Tomcat 8.0.15
Mojarra 2.2.8
Primefaces 5.1
RHEL 7.0

Answer 1

I don't think thats a good solution. The code should look more like this:
public TreeNode getRoot() {
checkSession();
if (root == null) {
root = new DefaultTreeNode(data, null);
}
return root;
}
To ensure that it's the same object (right scope of bean assumed)
Michael

Answer 2

As #BalusC wrote in his comment this exception occurs when backend tree is changed while UI tree is building.
When p:treeTable builds it calls getTree() method really many times, at least once for each category. If one of these calls receives a TreeNode object which does not equal the others this exception will be thrown.
In my code I made sure getTree() will always return the same TreeNode object if it was last called by the same user less than 10ms ago. That fixed it.
Better solution would be a fix in PrimeFaces that would make p:treeTable request TreeNode object only once.

Answer 3

Call following JS function onstart of <p:ajax event="select" onstart="func()" />.
function func(){
var originalVal = $('<YOUR_TREETABLE_ID>_selection').val();
var arr = originalVal.split(',');
$('<YOUR_TREETABLE_ID>_selection').val(arr[arr.length-1]);
}