Future và CompletableFuture khác nhau thế nào?

Future (Java 5) đại diện cho kết quả async. Hạn chế: get() block, không chain được, exception handling khó.

CompletableFuture (Java 8+) khắc phục: non-blocking, chain được, xử lý exception sạch.

CompletableFuture.supplyAsync(() -> fetchData())
  .thenApply(data -> process(data))            // chain transform
  .thenAccept(System.out::println)
  .exceptionally(ex -> { log(ex); return null; });

// Java 9+
cf.orTimeout(5, TimeUnit.SECONDS);
cf.completeOnTimeout(defaultValue, 5, TimeUnit.SECONDS);

// Chạy song song nhiều task
CompletableFuture.allOf(cf1, cf2, cf3).join();

Operator phổ biến: thenApply (map), thenCompose (flatMap), thenAccept (consumer), thenCombine (zip 2 CF), handle (xử lý cả success + error).

Java 21+: StructuredTaskScope là alternative hiện đại — quản lý lifecycle task rõ ràng, hoạt động tốt với Virtual Threads.

Future (Java 5) represents an async result. Limitations: get() blocks, no chaining, awkward exception handling.

CompletableFuture (Java 8+) addresses this: non-blocking, chainable, clean exception handling.

CompletableFuture.supplyAsync(() -> fetchData())
  .thenApply(data -> process(data))            // chain transform
  .thenAccept(System.out::println)
  .exceptionally(ex -> { log(ex); return null; });

// Java 9+
cf.orTimeout(5, TimeUnit.SECONDS);
cf.completeOnTimeout(defaultValue, 5, TimeUnit.SECONDS);

// Run many tasks in parallel
CompletableFuture.allOf(cf1, cf2, cf3).join();

Common operators: thenApply (map), thenCompose (flatMap), thenAccept (consumer), thenCombine (zip two CFs), handle (success + error).

Java 21+: StructuredTaskScope is the modern alternative — explicit task lifecycle, integrates well with Virtual Threads.