Validate if list in has at least one non-empty/null value

Question

I've a List<String> in my model:

private List<String> list;

// Add to list: "d","e","f","a","u","l","t"
// Getter.

I'm presenting it in the view as below:

<ui:repeat value="#{bean.list}" varStatus="loop">
    <h:inputText value="#{bean.list[loop.index]}"/>
</ui:repeat>

This works fine. Now I'd like to validate if the list contains at least one non-empty/null item. How can I create a custom validator for this?

score 4 · Accepted Answer · edited Jun 20 '20 at 09:12

This isn't easily possible with a custom validator. There's namely physically only one input component whose state changes with every iteration round. Your best bet is to hook on postValidate event of <ui:repeat> and then visit its children via UIComponent#visitTree() on the UIRepeat.

Here's a kickoff example:

<ui:repeat value="#{bean.list}" varStatus="loop">
    <f:event type="postValidate" listener="#{bean.validateOneOrMore}" />
    <h:inputText value="#{bean.list[loop.index]}"/>
</ui:repeat>

With this validateOneOrMore() method (again, just a kickoff example, this approach naively assumes that there's only one UIInput component in the repeater):

public void validateOneOrMore(ComponentSystemEvent event) {
    final FacesContext context = FacesContext.getCurrentInstance();
    final List<String> values = new ArrayList<>();

    event.getComponent().visitTree(VisitContext.createVisitContext(context), new VisitCallback() {
        @Override
        public VisitResult visit(VisitContext context, UIComponent target) {
            if (target instanceof UIInput) {
                values.add((String) ((UIInput) target).getValue());
            }
            return VisitResult.ACCEPT;
        }
    });

    values.removeAll(Arrays.asList(null, ""));

    if (values.isEmpty()) {
        event.getComponent().visitTree(VisitContext.createVisitContext(context), new VisitCallback() {
            @Override
            public VisitResult visit(VisitContext context, UIComponent target) {
                if (target instanceof UIInput) {
                    ((UIInput) target).setValid(false);
                }
                return VisitResult.ACCEPT;
            }
        });

        context.validationFailed();
        context.addMessage(null, new FacesMessage("Please fill out at least one!"));
    }
}

Note that it visits the tree twice; first time to collect the values and second time to mark those inputs invalid.

OmniFaces has an <o:validateOneOrMore> component which does a similar thing on fixed components, but it isn't designed for usage in dynamically repeated components.

Validate if list in has at least one non-empty/null value

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