Question

I have two very similar usecases, one works, and another one does not. I have checked the basic things mentioned in other answers (JSF2.1 on JBoss 7.1.1 with PrimeFaces 3.3).

First the sample which works:

<h:form id="processInstanceList">
    <p:dataTable id="instances" var="processInstance" value="#{processInstanceList}">
    ...
        <p:column>
            <h:commandLink value="#{msg.deleteButtonLabel}"
                action="#{runtimeService.deleteProcessInstance(processInstance.id, 'Cancelled by user')}">
        </h:commandLink>

with the action methods signature:

void deleteProcessInstance(String processInstanceId, String deleteReason);

and now the sample which does not work:

<h:form id="taskGrouplist">
    <p:dataTable id="groupTasks" value="#{groupTaskList}" var="v_task">
    ...
        <p:column>
            <h:commandLink value="&Uuml;bernehmen" action="#{taskList.claimTask(v_task)}"/>

with the action methods signature:

@Named
@RequestScoped
public class TaskList {
    public String claimTask(Task task);

on the second sample the task passed to the action method is always NULL. If I just pass an attribute of the task to the method, e.g. with #{taskList.claimTask(v_task.id)} (Task has a getId() method returning a String) and changing the action methods signature to public String claimTask(String id) … everything I pass in is NULL.

Why doesn’t this happen in the first sample? There I pass in two Strings and it works fine…

Answer 1

What is the scope of your RuntimeService bean?
Try to change your TaskList bean scope to ViewScoped or SessionScoped, here is why:

@RequestScoped: A request scoped bean has a lifetime of exactly one HTTP request/response.
So once your dataTable with commandLinks gets rendered (the HTTP request/response is over) you lose all the references for v_task parameters in your action=”#{taskList.claimTask(v_task)}” calls.

@ViewScoped: A view scoped bean lives as long as you’re interacting with the same JSF view.
Even after the rendering is over, because of the @ViewScope you still have your references on v_task object.