Find component by type in JSF

Question

My question is related to this one Get all hidden input fields in JSF dynamically but it's not the same as I want to work with JSF and not plain HTML, and assuming that I have the following in my .xhtml file:

<h:inputHidden id="name1" value="SomeValue1"/>
<h:inputHidden id="name2" value="SomeValue2"/>

I developed a small code where I tried to get all the h:inputHidden tags dynamically and print their values to the console, but the problem is that I can't figure out a way how to make everythning dynamic. In my code I should know the form id if I want to Iterate over the uicomponents, how can I iterate over all the UIComponent in the component tree ? (I tried UIViewRoot#getChildren() but i get only the first childrens).

Here is the code snippet:

// formId is the id of my form
List<UIComponent> components = FacesContext.getCurrentInstance().getViewRoot().findComponent("formId").getChildren();
// A List of UIComponent where I am adding my Hidden Inputs
List<UIComponent> hiddenComponents = new ArrayList<UIComponent>();

for (UIComponent component : components) {

    // using the hidden inputs type in JSF: HtmlInputHidden
    if (component instanceof HtmlInputHidden) {
        hiddenComponents.add(component);
    }

}

for (UIComponent component : hiddenComponents) {

    // Printing the hidden inputs values for demonstration purposes
    System.out.println(((HtmlInputHidden)component).getValue());

}

Alfred

Answer 1

You also need to iterate over children of children, and their children, etcetera. You see, it's a component tree.

Here's a kickoff snippet of an utility method which does exactly that using tail recursion:

public static <C extends UIComponent> void findChildrenByType(UIComponent parent, List<C> found, Class<C> type) {
    for (UIComponent child : parent.getChildren()) {
        if (type.isAssignableFrom(child.getClass())) {
            found.add(type.cast(child));
        }

        findChildrenByType(child, found, type);
    }
}

Here's how you could use it:

UIForm form = (UIForm) FacesContext.getCurrentInstance().getViewRoot().findComponent("formId");
List<HtmlInputHidden> hiddenComponents = new ArrayList<>();
findChildrenByType(form, hiddenComponents, HtmlInputHidden.class);

for (HtmlInputHidden hidden : hiddenComponents) {
    System.out.println(hidden.getValue());
}

Or, better, use UIComponent#visitTree() which uses the visitor pattern. The major difference is that it also iterates over iterating components such as <ui:repeat> and <h:dataTable> and restores the child state for every iteration. Otherwise you would end up getting no value when you have an <h:inputHidden> enclosed in such component.

FacesContext context = FacesContext.getCurrentInstance();
List<Object> hiddenComponentValues = new ArrayList<>();
context.getViewRoot().findComponent("formId").visitTree(VisitContext.createVisitContext(context), new VisitCallback() {
    @Override
    public VisitResult visit(VisitContext visitContext, UIComponent component) {
        if (component instanceof HtmlInputHidden) {
            hiddenComponentValues.add(((HtmlInputHidden) component).getValue());
            return VisitResult.COMPLETE;
        } else {
            return VisitResult.ACCEPT;
        }
    }
});

for (Object hiddenComponentValue : hiddenComponentValues) {
    System.out.println(hiddenComponentValue);
}

See also:

• How to collect values of an UIInput component inside an UIData component in bean's action method?
• How do I attach a FacesMessage from the backing bean to a specific field in a ui:repeat?
• Accessing dynamic UIComponents in JSF Managed Bean
• JSF 2 -- Save All Valid Component Values

After all, it's probably easiest to just bind them to a bean property the usual way, if necessary inside an <ui:repeat>:

<h:inputHidden id="name1" value="#{bean.name1}"/>
<h:inputHidden id="name2" value="#{bean.name2}"/>

Fractious

So I can call the findComponentsByType() method on the UIViewRoot directly? in case i don't konw the form ID ? e.g: findComponentsByType(context.getViewRoot(), hiddenComponents, HtmlInputHidden.class); is this correct ? also can we do the same with visitTree ? – Alfred

You can do so. It's also an UIComponent anyway. Note that I slightly renamed method/argument names to improve self-documentability. – Fractious

Yes I just noticed that, one last question and sorry for bothering you: UIComponent#visitTree() could we also invoke it directly on context.getViewRoot() ? – Alfred

UIViewRoot is an UIComponent. – Fractious

I think you forgot to modify the findComponentsByType name inside the findChildrenByType function. – Alfred