I am using DXA Web Application in java I have internal pages that are published and accessible via links on the home page. They are not published as part of the Navigation model. Is there a way to use the existing Navigation Action to resolve breadcrumb links for these pages. If not, I have created a custom Navigation Controller and resolving the links in handleGetNavigation().
All pages in the CMS are published as part of the navigation JSON, even if they are not 'visible' in the main navigation (prefixed with a number). As such it should be possible to build a breadcrumb for them (this is how it works in the .NET version at least), if not it sounds like a bug.
UPDATE: As you point out in the comment, an underscore can be added to prevent the item from being in the navigation JSON - I forgot about that. This prefix is really intended for system pages which are not displayed to the site visitor, so its not really intended for content pages, as you use it.