Contracts a core java library for dependency inversion, Dependency injection, Inversion of Control, Solid Principles: Single responsibility, Open-closed, Liskov substitution, Interface segregation, Dependency inversion. OpenSSF Best Practices. Java Module Support. Strong data encapsulation.
 | Mastering API Architecture: Design, Operate, and Evolve API-Based Systems (2022) by Gough, James, Bryant, Daniel, Auburn, Matthew |
 | Designing APIs with Swagger and OpenAPI (2022) by Ponelat, Joshua S., Rosenstock, Lukas L. |
 | Hacking APIs: Breaking Web Application Programming Interfaces (2022) by Ball, Corey J. |
 | Spring Boot 3 API Mastery: Write scalable, reactive, and secure APIs for microservices with Spring Boot 3 and Java 21 (English Edition) (2025) by Racca, Vincenzo |
 | API Design Patterns (2022) by JJ Geewax, Sarah Dawe, Manning Publications |
 | Modern API Development with Spring 6 and Spring Boot 3: Design scalable, viable, and reactive APIs with REST, gRPC, and GraphQL using Java 17 and Spring Boot 3 (2023) by Sourabh Sharma |
 | Practical API Design: Confessions of a Java Framework Architect (2008) by Tulach, Jaroslav |