Java流:flatMap返回对象流 [英] Java streams: flatMap returns Stream of Objects

问题描述

我有此代码:

List<Application> applications = this.applicationDao.findAll();
Collection<Pair<Application, FileObject>> files = applications.stream()
    .flatMap(app -> streamOfFiles.map(file -> Pair.of(app, file)));

其中 streamOfFiles 是 Stream< FileObject>

当前，我收到以下编译消息:

Currently, I'm getting this compilation message:

类型不匹配:无法从 Stream< Object> 转换为 Collection< Pair< Application，FileObject>>

有什么想法吗?

推荐答案

您似乎在这里缺少 collect :

Collection<Pair<Application, FileObject>> files = applications.stream()
        .flatMap(app -> files.stream().map(file -> Pair.of(app, file)))
        .collect(Collectors.toList()); // any collection you want

编辑 :由于 streamOfFiles 在单个 flatMap 操作中已被消耗，因此您应该优先使用一个< collection> .stream()代替，在那里为每个 app 应用重新创建流.

Edit: Since, streamOfFiles is getting consumed at a single flatMap operation, you should prefer to use a <collection>.stream() instead there to create the stream afresh for each app.

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