Sorted:

SQL vs. NoSQL Database: When to Use, How to Choose

DB Isolation Levels

Design Patterns Cheat Sheet

Spring Transaction Management: @Transactional In-Depth

Defining Unique Constraints in JPA

Spring Cloud Sleuth in a Monolith Application

JUnit 5: Writing Nested Tests

Guide to @ConfigurationProperties in Spring Boot

Kafka broker connection on local / AWS

Java Functional Interfaces Cheat Sheet + Examples