Java Stream : Flat from Pair to Pair

Question

我需要压缩 Pair<Application, FileObject[]> 的流, 到 Pair<Application, FileObject> 的流.

目前，我已经编码了:

List<Application> applications = this.applicationDao.findAll();
applications.stream()
    .map(app -> 
        new Pair<Application, FileObject[]>(
            app,
            this.massiveInterfaceService.getPendingDocuments(app)
        )
    );

所以，我需要的是获得 Pair<app, FileObject> 的流.

this.massiveInterfaceService.getPendingDocuments是:

public Stream<FileObject> getPendingDocuments(Application app) { /*...*/ }

有什么想法吗？

Answer 1

假设massiveInterfaceService.getPendingDocuments()返回 FileObject[] ，您可以创建这样的方法:

Stream<Pair<Application, FileObject>> flatten(Pair<Application, FileObject[]> pair) {
   return Arrays.stream(pair.getRight())
                .map(fileObject -> new Pair.of(pair.getLeft(), fileObject));
}

然后在您的流中使用它:

Stream<Pair<Application, FileObject>> stream =
   applications.stream()
        .map(app -> 
            Pair.of(app, this.massiveInterfaceService.getPendingDocuments(app)))
        .flatMap(this::flatten);

如果另一方面massiveInterfaceService.getPendingDocuments()返回 Stream<FileObject>

Stream<Pair<Application, FileObject>> stream =
   applications.stream()
        .flatMap(app -> 
            this.massiveInterfaceService
                .getPendingDocuments(app)))
                .map(fileObject -> Pair.of(app, fileObject)));

从你的问题中不清楚哪个是正确的。