Java 流 : flatMap returns Stream of Objects

Question

我有这段代码:

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

哪里streamOfFiles是一个 Stream<FileObject>

目前，我收到这条编译消息:

Type mismatch: cannot convert from Stream<Object> to Collection<Pair<Application,FileObject>>

有什么想法吗？

Answer 1

您似乎缺少 collect那里:

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:因为，streamOfFiles正在消耗单个 flatMap操作，您应该更喜欢使用 <collection>.stream()而是为每个 app 重新创建流.