组合多个CompletableFutures

Question

我有以下组成部分：

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ENDPOINTS并修饰一些数据。现在，我试图通过使用CompletableFutures来实现这种非阻塞性，而我之前从未真正使用过。

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为`new JobInfo（jobsResult，jobDetails）时，如何在此处创建CompletableFuture ？！

如我所说，我是新手，也许我的方法不好，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)

你要

CompletableFuture<JobInfo>

补充说明：jobDetailsFuture只能在完成后才能jobsResultFuture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var）-> List<JobDetails>通过thenApply
3. List<JobDetails>+ CompletableFuture<JobsResult>（作为捕获的var）-> JobInfo通过thenApply

您可以简单地通过get()那些映射器函数内部展开期货，因为由于当时祖先期货的依赖关系，保证期货在那一点已完成。

使用thenCombine和减少流的其他方法是可能的，但是更加冗长，并且会创建更多的中间期货。