CompletableFuture | thenApply vs thenCompose

thenApply is used if you have a synchronous mapping function.

CompletableFuture<Integer> future = 
    CompletableFuture.supplyAsync(() -> 1)
                     .thenApply(x -> x+1);

thenCompose is used if you have an asynchronous mapping function (i.e. one that returns a CompletableFuture). It will then return a future with the result directly, rather than a nested future.

CompletableFuture<Integer> future = 
    CompletableFuture.supplyAsync(() -> 1)
                     .thenCompose(x -> CompletableFuture.supplyAsync(() -> x+1));