Question

What would the method facesContext.isValidationFailed() return after the Render Response Phase when the validation fails? It returns false for me in this case.

Answer 1

It will only return true when FacesContext#validationFailed() has been called by the JSF validation internals or by your own code as follows:

FacesContext.getCurrentInstance().validationFailed();

As far JSF internal code is concerned, only UIInput#processValidators() and UIViewParameter#processValidators() will implicitly call this method whenever a ValidatorException has been caught.

If it returns false for you, then you’re apparently doing validation in a non-standard way. For example inside the action method, while you should be using a real Validator for this.