Spring Boot 3.x is now outside OSS support. Here's how to calculate the risk, choose the right 4.x landing zone, automate the mechanical work with OpenRewrite, and complete the migration without turning it into a six-month rewrite.
AI scanners are flooding the Spring ecosystem with patch PRs faster than any team can review. Build an automated remediation pipeline instead: Dependabot or Renovate tuned for Spring Boot parent POMs and BOMs, a Testcontainers regression gate that decides which bumps are safe, and canary deployments for minor framework upgrades.
A practical Spring Framework 6 to 7 migration guide covering the Jakarta EE 11 baseline, removed and deprecated APIs, AOT and GraalVM changes, BeanRegistrar and proxy lifecycle changes, JSpecify null safety, testing and security implications, an upgrade checklist, and an AI prompt to scan your project.
The Singleton pattern guarantees exactly one instance of a class — but Java's threading model, serialization, and reflection make it harder than it looks. Complete guide: all 6 implementations (Eager, Lazy, synchronized, DCL, Holder, Enum), thread-safety analysis, Spring singletons, pitfalls, and when NOT to use it.
The Prototype pattern lets you clone objects without depending on their concrete classes. Complete Java guide: Cloneable pitfalls, deep vs shallow copy, copy constructors, serialization-based cloning, JDK usage, and when to use each approach.
The Builder pattern separates complex object construction from its representation, eliminating telescoping constructors and invalid partial state. Complete Java guide with runnable examples, Lombok @Builder, JDK usage (StringBuilder, Stream.Builder), pitfalls, and FAQs.
The Abstract Factory pattern lets you create families of related objects without specifying their concrete classes. Complete Java guide with runnable cross-platform UI example, JDK usage, comparison with Factory Method, pitfalls, and FAQs.
The Factory Method pattern lets subclasses decide which object to create, eliminating if/else creation logic and making your codebase open for extension without modification. Complete guide with runnable Java examples, JDK usage, Spring Boot integration, pitfalls, and FAQs.
Of every breaking change in the Spring Boot 2 → 3 era, the removal of WebSecurityConfigurerAdapter generated the most confused stack traces I've debugged — because security configuration is the one place where "it compiles and runs" tells you almost nothing about whether it still protects anything. This guide migrates Spring Security 5 configurations to the 6.x component model (Spring Boot 3.x), covers what tightens further in Spring Security 7 (Spring Boot 4), and flags the places where a mechanical conversion quietly changes your authorization behaviour.
Spring Boot 4 finally forced the issue: RestTemplate, in maintenance mode since Spring 5, is out of the recommended path, and codebases full of getForObject() and exchange() calls need a plan. The good news is that RestClient (introduced in Spring 6.1 / Boot 3.2) was designed as the synchronous successor, so this migration is mostly mechanical — if you know the method-by-method mapping and the three places where behaviour quietly differs. This guide gives you both.