JavaServer Faces – Find component recursively

In my current project I had to implement a jsf validator regarding 2 jsf-components. Unfortunately the validate method of the Validator Interface allows only one component as parameter.

To realise a validator for 2 fields I needed a way to get the value of the second involved component.

Therefore I added the id of the second component as parameter.

<t:inputTextarea id="comp1" ... >
    <f:validator validatorId="myValidator" />
    <f:attribute name="compId" value="comp2" />
</t:inputTextarea>
<t:inputTextarea id="comp2" ... />

The idea was to use the method

    UIViewRoot.findComponent(clientID)

to get the needed component.

To my surprise, sometimes null was returned, mainly when used in nested DataTables. So I walked through the complete component tree and looked “by hand” for the component … and no surprise – it exists!

To solve this problem (looks like a bug in JSF 1.1) I wrote a recursive variant of the findComponent method. This method walks through the complete JSF component tree searches for the component (via clientId) and returns it.

/**
 * Traverses the componenttree recursively and
 * returns the desired component
 *
 * @param context
 * @param comp
 * @param clientId
 * @return
 */
public UIComponent findComponentRecursively(FacesContext context, UIComponent comp, String clientId) {
 
    if (clientId.equals(comp.getClientId(context))) {
        return comp;
    } else {
        if (comp.getChildCount() &gt; 0) {
            for (Iterator it = comp.getChildren().iterator(); it.hasNext();) {
                UIComponent component = (UIComponent) it.next();
                UIComponent res = findComponentRecursively(context, component, clientId);
                if (res != null) {
                    return res;
                }
            }
        }
    }
    return null;
}

For performance reasons I use the following method. First it tries to look for the desired component directly and uses the recursive variant as fallback.

    /**
     * This method finds a component in the JSF-Tree by its
     * complete id. Due to a bug in JSF a component is not
     * always found by @link UIViewRoot.findComponent.
     * Therefore findComponentRecursively is called if needed.
     *
     * @param context
     * @param comp
     * @param clientId
     * @return
     */
    public UIComponent findComponent(FacesContext context, String clientId) {
        UIComponent newComp = (UIComponent) context.getViewRoot().findComponent(clientId);
        if (newComp == null) {
            newComp = (UIInput) JSFHelper.getInstance().findComponentRecursively(context, context.getViewRoot(),
                    clientId);
        }
        return newComp;
    }

I hope this saves you some time when struggling with the same problem.

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Autor: Andreas Frey
Datum: Friday, 17. October 2008 12:03
Trackback: Trackback-URL Themengebiet: JavaServer Faces

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2 Kommentare

  1. Matthias Bohlen
    Wednesday, 12. November 2008 23:55
    1

    There are people who think that JSF is broken, so broken that it cannot be fixed and has to be rewritten. How is your experience?

  2. Andreas Frey
    Friday, 14. November 2008 16:23
    2

    I don’t think JSF is broken. It is a framework addressing most of the standard problems. Sure i miss some things, but it is great to develop fast Web Applications – and most problems can be solved – with some effort.

    Like all frameworks it addresses some problems and solves them … but nothing more

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