Structured Concurrency in Java 21: What It Fixes and Why It Exists

Java 21 introduces structured concurrency (JEP 453) via StructuredTaskScope to address the messy failure handling, inconsistent cancellation, and scattered cleanup inherent in traditional CompletableFuture-based concurrent code. The new model groups related tasks into a single scope with explicit failure policies and automatic cleanup on scope exit, making the code's lifecycle easier to reason about and review. It is best suited for I/O-heavy fan-out and service aggregation patterns rather than CPU-bound or long-lived background work.