Compare1d.java

class Wrappers {
    // I/O operations: non-blocking, asynchronous
    <T> CompletableFuture<T> fetchFromDb(Class<T> entityClass, long id) { return null; }
    CompletableFuture<String> sendHttpGet(String url) { return null; }
    CompletableFuture<Void> sendEmail(String to, String content) { return null; }

    // the bussines logic: asynchronous
    CompletableFuture<Void> runBusinessProcess() {
        // thenCompose: also known as flatMap, combines two futures
        return fetchFromDb(User.class, 42).thenCompose(user -> {
            // storing the intermediate result in variables
            CompletableFuture<String> httpResult = 
              sendHttpGet("http://profile_service/get/" + user.getProfileId());
              
            return httpResult.thenCompose(profile ->
                    sendEmail(user.getEmail(), "Your profile is: " + profile));
        });
    }
}