java-8 - 组合多个 CompletableFuture

Question

我有以下组件:

private JobInfo aggregateJobInfo() {
    final JobsResult jobsResult = restClient().getJobs();
    final List<String> jobIds = extractJobIds(jobsResult);

    //fetch details, exceptions and config for each job
    final List<JobDetails> jobDetails = jobIds.stream().map(jobId -> {
        final JobDetailResult jobDetailResult = restClient().getJobDetails(jobId);
        final JobExceptionsResult jobExceptionsResult = restClient().getJobExceptions(jobId);
        final JobConfigResult jobConfigResult = restClient().getJobConfig(jobId);
        return new JobDetails(jobDetailResult, jobExceptionsResult, jobConfigResult);
    }).collect(Collectors.toList());
    return new JobInfo(jobsResult, jobDetails);
}

private static List<String> extractJobIds(final JobsResult jobsResult) {
    final ArrayList<String> jobIds = new ArrayList<>();
    jobIds.addAll(jobsResult.getRunning());
    jobIds.addAll(jobsResult.getFinished());
    jobIds.addAll(jobsResult.getCanceled());
    jobIds.addAll(jobsResult.getFailed());
    return jobIds;
}

它只是调用一些端点并聚合一些数据。现在我试图通过使用 CompletableFutures 来实现非阻塞，我之前并没有真正使用过它。

private CompletableFuture<JobInfo> aggregateJobInfo() {
    final CompletableFuture<JobsResult> jobsResultFuture = restClient().getJobs();
    final CompletableFuture<List<String>> jobIdsFuture = jobsResultFuture.thenApply(JobInfoCollector::extractJobIds);

     //fetch details, exceptions and config for each job
    final CompletableFuture<List<CompletableFuture<JobDetails>>> jobDetailsFuture = jobIdsFuture.thenApply(jobIds -> {
        return jobIds.stream().map(jobId -> {
            final CompletableFuture<JobDetailResult> jobDetailsResultFuture = restClient().getJobDetails(jobId);
            final CompletableFuture<JobExceptionsResult> jobExceptionsFuture = restClient().getJobExceptions(jobId);
            final CompletableFuture<JobConfigResult> jobConfigFuture = restClient().getJobConfig(jobId);
            return jobDetailsResultFuture.thenCompose(jobDetailResult -> {
                return jobExceptionsFuture.thenCombine(jobConfigFuture, (jobExceptionsResult, jobConfigResult) -> {
                    return new JobDetails(jobDetailResult, jobExceptionsResult, jobConfigResult);
                });
            });

        }).collect(Collectors.toList());
    });
    return null;

我的问题是当 JobInfo 是 `new JobInfo(jobsResult, jobDetails)?! 时如何在这里创建 CompletableFuture？!

正如我所说，我对此很陌生，也许我的方法不好并且有更好的解决方案？

任何想法表示赞赏，谢谢

第一个工作版本:

private CompletableFuture<JobInfo> aggregateJobInfo() {

    final CompletableFuture<JobsResult> jobsResultFuture = restClient().getJobs();
    final CompletableFuture<List<String>> jobIdsFuture = jobsResultFuture.thenApply(JobInfoCollector::extractJobIds);

    final CompletableFuture<List<CompletableFuture<JobDetails>>> jobDetailsFutureListFuture =
            jobIdsFuture.thenApply(jobIds -> jobIds.stream().map(jobId -> {
                final CompletableFuture<JobDetailResult> jobDetailsResultFuture = restClient().getJobDetails(jobId);
                final CompletableFuture<JobExceptionsResult> jobExceptionsFuture = restClient().getJobExceptions(jobId);
                final CompletableFuture<JobConfigResult> jobConfigFuture = restClient().getJobConfig(jobId);
                return jobDetailsResultFuture.thenCompose(jobDetailResult ->
                        jobExceptionsFuture.thenCombine(jobConfigFuture, (jobExceptionsResult, jobConfigResult) ->
                                new JobDetails(jobDetailResult, jobExceptionsResult, jobConfigResult)));
            }).collect(Collectors.toList()));

    return jobDetailsFutureListFuture.thenCompose(jobDetailsFutures ->
            CompletableFuture.allOf(jobDetailsFutures.toArray(
                    new CompletableFuture[jobDetailsFutures.size()])).thenApply(aVoid ->
                    jobDetailsFutures.stream()
                            .map(CompletableFuture::join)
                            .collect(Collectors.toList())))
            .thenApply(jobDetails -> jobsResultFuture.thenApply(jobsResult ->
                    new JobInfo(jobsResult, jobDetails)))
            .join();
}

Answer 1

你有:

• CompletableFuture<JobsResult> jobsResultFuture
• CompletableFuture<List<CompletableFuture<JobDetails>>> jobDetailsFuture
• JobInfo(JobsResult a, List<JobDetails> b)

你想要

CompletableFuture<JobInfo>

额外观察:jobDetailsFuture仅当 jobsResultFuture 时才能完成已完成。

因此您可以实现以下内容:

1. List<CompletableFuture<JobDetails>> -> Void通过 allOf在thenCompose
2. Void + List<CompletableFuture<JobDetails>> (作为捕获的变量)-> List<JobDetails>通过 thenApply
3. List<JobDetails> + CompletableFuture<JobsResult> (作为捕获的变量)-> JobInfo通过 thenApply

您可以通过get()简单地打开 future 。在这些映射器函数内部，因为由于当时其祖先 future 的依赖关系，future 保证在该点完成。

使用 thenCombine 的其他方法流减少是可能的，但更冗长并创造更多的中间 future 。