Hibernate

Sits between Java objects and the relational database — session.save(user) becomes a SQL INSERT. HQL/JPQL is the query language (SQL-like). Famous pitfalls: N+1 queries (loop triggering a query per iteration), lazy loading exception outside the session. Major competitors: jOOQ (type-safe SQL builder), MyBatis (more SQL-explicit), Quarkus/Hibernate Reactive (modern). Gavin King later architected the Ceylon language + Red Hat.