CompletableFuture Composition

Compare CompletableFuture Composition with a common alternative (angle 5). How do you decide in a design review?

Answers use simple, clear English.

Quick interview answer

Baseline: supplyAsync runs async task; thenApply transforms; thenCompose flattens nested futures; allOf waits for batch. Exceptionally/handle for error paths.

Detailed answer

Baseline: supplyAsync runs async task; thenApply transforms; thenCompose flattens nested futures; allOf waits for batch. Exceptionally/handle for error paths. Prefer when pros dominate: Composable async without raw callbacks; integrates with thread pools.. Avoid when: Default ForkJoinPool.commonPool() shared — inject Executor for isolation.. Core: supplyAsync runs async task; thenApply transforms; thenCompose flattens nested futures; allOf waits for batch. Exceptionally/handle for error paths. Real-time example: Aggregate microservice responses: CompletableFuture.allOf(userF, ordersF).thenApply(...). Pros: Composable async without raw callbacks; integrates with thread pools. Cons: Default ForkJoinPool.commonPool() shared — inject Executor for isolation. Common mistakes: Blocking get() on async chain in request thread; lost exceptions without handle. Best practices: Specify executor for IO; use orTimeout/join with timeout in Java 9+. Audience level: Tech Lead.

Full explanation

supplyAsync runs async task; thenApply transforms; thenCompose flattens nested futures; allOf waits for batch. Exceptionally/handle for error paths.

Real example & use case

Aggregate microservice responses: CompletableFuture.allOf(userF, ordersF).thenApply(...).

Pros & cons

Pros: Composable async without raw callbacks; integrates with thread pools. Cons: Default ForkJoinPool.commonPool() shared — inject Executor for isolation.

Common mistakes

Blocking get() on async chain in request thread; lost exceptions without handle.