Building REST APIs with Spring Boot 4.0

I'd describe this fast-paced book as the perfect practical tutor for Java developers who are curious to develop apps, and not just read about them. All chapters are working sets, where you write code, run it, break it deliberately, and fix it. There are no long theory sections, and no abstract architecture talk. It's all connected from the first command to the final deployable JAR. It's all about one main thing, your first REST API, and it takes you through Spring Boot 4.0 with Java 21, including configuration management, Spring Data JPA, structured error handling, operational monitoring with Actuator, role-based security with Spring Security 7.0, three layers of automated testing, and executable JAR packaging. There's even a whole chapter just on troubleshooting, so you can get past those tricky spots that always seem to trip up beginners in the real projects. This book doesn't aim to cover everything Spring Boot has to offer. Instead, it focuses on the essentials, and it does this in a way that's easy to understand. There's plenty of code to get your hands onto, plus tests to pass and explanations to help you get the most out of it. When you're done, you'll have a production-ready API that's fully secured and tested, and the confidence to take it further on your own. Key LearningsCreate a fully functional REST API from scratch using Spring Boot 4.0. Use Java 21 record classes to configure type-safe, validated application properties. Use derived query methods to persist and query data with Spring Data JPA. Manage multiple runtime environments using Spring Profiles and profile-specific properties. Use Spring Boot Actuator and Micrometer to expose health metrics and info endpoints. Use role-based HTTP authentication to secure REST endpoints. Use test slices to test controllers, repositories and full-stack behaviour. You can package a Spring Boot application as a self-contained, deployable executable JAR file. You will diagnose and resolve common Spring Boot startup, configuration and security failures.