There is no point to diagramming something when all you need to do is add semi colons to the text in the diagram and compile.

But this may be an artefact of the fact that only simple examples are used in texts as I can see the utility of these diagrams when there is complicated set of steps at a higher level than a single class or that involves interaction with numerous classes

When you see words like JDBC, DAO, etc in diagram instead of just data base access? Aren't the use ( UML, whatever.. ) diagrams supposed to show use cases, what, etc instead of one of hundreds (thousands?) of possibles ways to implement a solution? It says Spring/JSP project but what if things change next week? How valid it is then? Not to blame the book but solutions should work not matter what the supporting architecture is.