Java 25 finalizes JEP 511: import module java.base; replaces a page of imports. See what it does, which imports win when names clash, why import module java.sql does not give you java.base, why java.se needs --add-modules, and when to use it.
Java 25 finalizes JEP 513: statements before super() or this(). See the old error and workaround, validation and argument preparation, the parent-calls-child bug it fixes, and the compile errors that remain, with JDK 25 and 27 wordings compared.
Java 25 finalizes JEP 512: void main() in a file with no class, the java.lang.IO helper, implicit java.base imports, the measured launcher order, and a private-constructor difference between JDK 25 and 27 — every claim compiled and run, with transcripts.
Spring Boot 4 i18n with MessageSource and LocaleResolver: Marathi and Hindi bundles, Accept-Language vs a cookie, MessageFormat apostrophes and digits, and localized validation and ProblemDetail.
Two databases in one Spring Boot 4.1 application: a DataSource, Flyway, EntityManagerFactory and transaction manager per database, package-based repository scanning, and every way it fails, each run and quoted from a committed transcript.
Spring events are blocking method calls, and that one fact explains the surprises: a listener that rolls the publisher back, an AFTER_COMMIT listener that silently never runs, and an async listener that sees a different world. Every claim is reproduced on Spring Boot 4.1 with a committed transcript, including a rollback that proves AFTER_COMMIT semantics.
Build a real Spring Boot 4.1 starter from an empty directory: the two-jar layout, AutoConfiguration.imports, @ConditionalOnMissingBean back-off, configuration metadata, an optional Jackson 3 integration, and the ApplicationContextRunner test that passes while the starter is broken. Every claim comes from a committed transcript.
Spring Boot 4 refuses to start with "The dependencies of some of the beans in the application context form a cycle". This article reproduces the failure, reads the report, and applies four fixes (redesign, events, @Lazy, ObjectProvider), plus what allow-circular-references really does on Spring Framework 7.0.9. Every claim comes from a committed test transcript.
Every Spring bean lifecycle callback printed in order from a real run, @PostConstruct running before the proxy exists, the non-static BeanPostProcessor warning, SmartLifecycle phases measured, and a request in flight during graceful shutdown with virtual threads. Tested on Spring Boot 4.1.1, Spring Framework 7.0.9 and Java 25.
Instance counts for singleton, prototype, request, session and application scope taken from real runs, the prototype-in-singleton trap and four ways to fix it, a singleton leaking one caller's data into another, and request scope without a proxy failing at start-up. Tested on Spring Boot 4.1.1, Spring Framework 7.0.9 and Java 25.