JSF2: action and actionListener

Question

From this answer by BalusC here Differences between action and actionListener, Use actionListener if you want have a hook before the real business action get executed, e.g. to log it, and/or to set an additional property (by <f:setPropertyActionListener>,. However when I decide to write some code to test this, the result is a bit different. Here is my small code

<h:form id="form"> 
   <h:panelGroup id="mygroup">
     <p:dataTable id="mytable" value="#{viewBean.foodList}" var="item">
         <p:column>
             #{item}
         </p:column>
         <p:column>
             <p:commandButton value="delete" 
                        action="#{viewBean.delete}"
                        update=":form:mygroup">
                 <f:setPropertyActionListener target="#{viewBean.selectedFood}"
                                              value="#{item}"/>
             </p:commandButton>
         </p:column>
      </p:dataTable>
   </h:panelGroup>
</h:form>

Here is my bean

@ManagedBean
@ViewScoped
public class ViewBean {
    private List<String> foodList;
    private String selectedFood;

    @PostConstruct
    public void init(){

        foodList = new ArrayList<String>();
        foodList.add("Pizza");
        foodList.add("Pasta");
        foodList.add("Hamburger");
    }

    public void delete(){
        foodList.remove(selectedFood);
    }
    //setter, getter...
}

According to BalusC, actionListener is more suitable here, but my example show otherwise.

The above code work great with action, but if I switch over to actionListener, then it does not quite work. It will take two clicks for me to delete an entry of this table using actionListener, while if I use action, it delete entry every time I click the button. I wonder if any JSF expert out there can help me understand action vs actionListener

Note If I switch to actionListener, my delete method become public void delete(ActionEvent actionEvent)

@mrembisz: I did use `update` of the `p:commandButton`, so I think there is a related to primefaces, but I am not 100% sure. Will try to look deeper. — Thang Pham, Dec 30 '11 at 19:59
@mrembisz: Mr.J4mes did confirm `h:commandButton` shows the same behavior. — Thang Pham, Dec 30 '11 at 20:19

score 16 · Accepted Answer · edited May 23 '17 at 12:15

You're confusing action with actionListener. The actionListener runs always before the action. If there are multiple action listeners, then they run in the same order as they have been registered. That's why it doesn't work as expected when you use actionListener to call the business action and <f:setPropertyActionListener> to set (prepare) a property which is to be used by the business action. This problem was pointed out and fixed in your previous question Is this Primefaces bug or Mojarra/MyFaces bug.

Whatever you have in the delete() method is clearly a business action and should be invoked by action instead. A business action typically invokes an EJB service and if necessary also sets the final result and/or navigates to a different view.

Mr.J4mes · Answer 2 · 2011-12-30T21:20:46.463

4

I tried your example with original JSF's tags <h:commandButton> but I also get the same symptom. I believe if you specify actionListener attribute and at the same time, declare another listener with <f:setPropertyActionListener>, the listener in the attribute actionListener will be fired before the other.

UPDATE: I test my assumption with the following code:

Change your delete function to this one:

public void delete(){
    this.selectedFood = "Chicken";
    //foodList.remove(selectedFood);
}

Add <h:outputText id="food" value="#{viewBean.selectedFood}" /> inside <h:panelGroup id="mygroup">.

You will see that the outputText is always Chicken.

edited Dec 30 '11 at 21:20

answered Dec 30 '11 at 20:07

Mr.J4mes

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I actually gradually drifted to that conclusion as well. I realized that `selectedFood` is null when the `delete` method get invoke. Does that mean what `BalusC` said is wrong? `ohh noooo!!!!!!!!!!!!!` – Thang Pham Dec 30 '11 at 20:17
He's not wrong :P. I think you mis-understood his saying. He was trying to explain the different usages of `action` and `actionListener`. `` is one kind of `actionListener` and he mentioned it to show how you can `set an additional property` in his example. In general, `actionListener` always get fired before `action`. That's why it always work with `action`. – Mr.J4mes Dec 30 '11 at 20:22
he said to use `actionListener if you want have a hook before the real business action get executed`. So is `` not the `hook` before business action which is `delete`? When I read that sentence, I thought he mean `` will get executed before `delete` – Thang Pham Dec 30 '11 at 20:28
The action he mentioned in `a hook before the real business action` is your `delete` method only if it is declared like this `action="#{viewBean.delete}"`. If you declared it with `actionListener`, it became a listener which is no longer a `real business action`. – Mr.J4mes Dec 30 '11 at 20:39

JSF2: action and actionListener

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