Java: improving the quality of the code (preconditions, IDEA QAPlug, GitHub Codacy integration)

Hello!
I continue a series of publications on the Java Enterprise training project Topjava (Maven / Spring / Security / JPA (Hibernate) / Rest (Jackson) / Bootstrap (CSS) / jQuery + plugin).

A small topic of the fourth lesson: improving the quality of the code

Useful links:

1. Contract Programming , Contract Programming
2. Comparison Preconditions in Java
3. QAPlug vs FindBugs
4. QAPlug tutorials
5. Codacy home

Previous publications:

• In the wake of Spring Pet Clinic. Maven / Spring Context / Spring Test / Spring ORM / Spring Data JPA
• We test Spring Rest controllers: simpler, shorter, more reliable. Spring Security Test + JSON Matcher
• Spring Security 4 + CSRF (adding a cross-site request forgery protection project to Spring)
• Java Spring application in PaaS-platform Heroku in 14 minutes

Thanks for attention!