https://devops-monk.com/tags/java/Recent content in Java on Devops MonkHugoen-usSun, 03 May 2026 00:00:00 +0000https://devops-monk.com/2026/05/spring-boot-auto-configuration-deep-dive/Sun, 03 May 2026 00:00:00 +0000https://devops-monk.com/2026/05/spring-boot-auto-configuration-deep-dive/“Spring Boot is magic” is something you hear a lot. Add spring-boot-starter-data-jpa and suddenly you have a working DataSource, a JpaTransactionManager, and a LocalContainerEntityManagerFactoryBean — without writing a single @Bean method. Understanding how this actually works turns the magic into a tool you can control, debug, and extend. The Entry Point: @EnableAutoConfiguration @SpringBootApplication is a shorthand for three annotations: @Configuration @EnableAutoConfiguration // this is the one that matters here @ComponentScan public class MyApplication { public static void main(String[] args) { SpringApplication.https://devops-monk.com/tutorials/spring-boot/introduction-to-spring-boot/Sun, 03 May 2026 00:00:00 +0000https://devops-monk.com/tutorials/spring-boot/introduction-to-spring-boot/You want to build a Java web application or REST API. You’ve heard everyone uses Spring Boot. But what is it exactly, and why does it exist? This article answers that — clearly — before writing a single line of code. What Is Spring Boot? Spring Boot is an opinionated framework for building Spring-based Java applications with minimal configuration. Break that down: Spring-based — it sits on top of the Spring Framework, which has been the dominant Java application framework since 2003 Minimal configuration — you describe what you want (a web app, a database connection), and Spring Boot figures out how to set it up Opinionated — it makes sensible default choices so you don’t have to make every decision yourself The one-line version: Spring Boot lets you go from a blank project to a running application in minutes, with production-ready defaults built in.https://devops-monk.com/tutorials/spring-boot/spring-boot-jspecify-null-safety/Sun, 03 May 2026 00:00:00 +0000https://devops-monk.com/tutorials/spring-boot/spring-boot-jspecify-null-safety/NullPointerException is the most common runtime error in Java. JSpecify is the standardized solution — annotate your APIs and get compile-time null safety. Spring Framework 7 adopts JSpecify throughout, and your code can too. The Problem // Is this safe? You don't know without reading the implementation. public Order findById(UUID id) { return repository.findById(id).orElse(null); // returns null! } // The caller has no warning: Order order = service.findById(id); order.cancel(); // ← NullPointerException if not found Without null annotations, every method call is potentially null — you write defensive code everywhere, or you miss a case and get a NPE in production.https://devops-monk.com/2026/05/spring-boot-migration-guide/Sun, 03 May 2026 00:00:00 +0000https://devops-monk.com/2026/05/spring-boot-migration-guide/Many teams are still running Spring Boot 2.7.x. Spring Boot 2.x reached end of life in November 2023, which means no more security patches. The jump to 4.0 is two generations, and the breaking changes are real — but they are also well-documented and mostly automatable. This guide walks through the migration in stages: 2.x → 3.0 first, then 3.x incremental updates, then 4.0. Each section lists what breaks and how to fix it.https://devops-monk.com/2026/05/spring-boot-4-complete-guide/Sun, 03 May 2026 00:00:00 +0000https://devops-monk.com/2026/05/spring-boot-4-complete-guide/Spring Boot 4.0 was released on November 20, 2025. It is built on Spring Framework 7 and represents the most significant shift in the Spring ecosystem since the Jakarta EE migration in Spring Boot 3. The headline change is full modularisation — the single spring-boot-autoconfigure JAR has been split into 70+ granular modules. But that is just the start. This guide covers every change that matters, what breaks on upgrade, and what is genuinely new and useful.https://devops-monk.com/tutorials/spring-boot/spring-boot-project-structure/Sun, 03 May 2026 00:00:00 +0000https://devops-monk.com/tutorials/spring-boot/spring-boot-project-structure/A Spring Boot project looks simple on the surface but has a specific structure with specific conventions. Understanding it upfront saves hours of confusion later. The Standard Layout order-service/ ├── pom.xml ├── mvnw # Maven Wrapper script (Unix) ├── mvnw.cmd # Maven Wrapper script (Windows) ├── .mvn/ │ └── wrapper/ │ └── maven-wrapper.properties └── src/ ├── main/ │ ├── java/ │ │ └── com/devopsmonk/orderservice/ │ │ └── OrderServiceApplication.java │ └── resources/ │ ├── application.https://devops-monk.com/2026/05/spring-boot-vs-quarkus/Sun, 03 May 2026 00:00:00 +0000https://devops-monk.com/2026/05/spring-boot-vs-quarkus/Every year, someone asks: “Should we use Spring Boot or Quarkus?” In 2026, both frameworks are mature, both run natively, and both work well on Kubernetes. The differences come down to developer experience, ecosystem size, and specific performance characteristics. This is an honest comparison with real numbers, not marketing claims. The Frameworks at a Glance Spring Boot 4 (November 2025): Built on Spring Framework 7. The de-facto standard for enterprise Java.https://devops-monk.com/2026/05/spring-boot-interview-questions/Sun, 03 May 2026 00:00:00 +0000https://devops-monk.com/2026/05/spring-boot-interview-questions/These are the questions that actually come up in Spring Boot interviews — at startups, scale-ups, and large enterprises. Each answer explains the concept clearly, with the level of depth an interviewer expects from a mid-level or senior developer. Questions are grouped by topic. For junior roles, focus on sections 1–3. For senior roles, everything here is fair game. Section 1: Core Fundamentals Q1. What is the difference between Spring and Spring Boot?https://devops-monk.com/tutorials/spring-boot/spring-boot-4-whats-new/Sun, 03 May 2026 00:00:00 +0000https://devops-monk.com/tutorials/spring-boot/spring-boot-4-whats-new/Spring Boot 4.0 (November 2025) is a major release built on Spring Framework 7 and Java 17+. It’s the most significant Spring release since Boot 3’s Jakarta EE migration. This article covers every change that affects a practicing developer. Minimum Requirements Spring Boot 3.x Spring Boot 4.0 Java 17 17 (baseline), 21 recommended Spring Framework 6.x 7.x Jakarta EE 10 11 Tomcat 10.x 11.x Hibernate 6.x 7.x Gradle (if used) 7.https://devops-monk.com/tutorials/spring-boot/first-spring-boot-application/Sun, 03 May 2026 00:00:00 +0000https://devops-monk.com/tutorials/spring-boot/first-spring-boot-application/In this article you’ll create a Spring Boot application, add a REST endpoint, and run it — all in under 10 minutes. Then you’ll understand exactly what each piece does. What you’ll build: A Spring Boot app that responds to GET /hello with "Hello, Spring Boot!". Prerequisites JDK 21 or higher installed (java -version to verify) Maven 3.9+ installed (mvn -version to verify) An IDE — IntelliJ IDEA (recommended), VS Code with Java extension, or Eclipse Step 1: Generate the Project Go to start.