This blog is about practical applications of Category Theory to the development of Java + Spring applications. I am looking at a design approach to simplify the development of web applications. Traditionally, this kind of back-office application is based on the Web 1.0 technology stack, using Spring Boot and Thymeleaf. My approach is to keep using Spring Boot but replace the generation of HTML with J2HTML and higher-order views. From a Category Theory point of view, we can look at web applications as mappings from the Category of Business Entities and the Category of UI Widgets. If we go one step further, both business entities and UI widgets are mapped to Java classes. Thus, we can view a web application (or a part of it) as an endofunctor in the Category of Java Classes. We define the View-functor as follows: domain(V) - Java classes representing business entities - e.g., Invoice, User - and, codomain(V) - Java functions that render the business entity as a DomContent object (DomCont