How to sort files in a stream by partial filename?

Question

I use the following to sort files first by name, then by modification date:

Files.list(Paths.get(importDir))
        .map(Path::toFile)
        .sorted(Comparator.comparing(File::getName).thenComparingLong(File::lastModified))
        .forEachOrdered(file -> System.out.println(file.getName()));

Question: how can I refactor the File::getName part to only compare based on partial filename, like: StringUtils.substringBefore(file.getName(), "_")?

Mureinik · Accepted Answer · 2021-11-30T11:23:23.383

1

You could replace the method reference with a lambda expression on the File object, although you'll have to specify the types (see the additional discussion here):

Files.list(Paths.get(importDir))
     .map(Path::toFile)
     .sorted(Comparator.<File, String> comparing(f -> StringUtils.substringBefore
                                                      (f.getName(), "_"))
                       .thenComparingLong(File::lastModified))
     .forEachOrdered(file -> System.out.println(file.getName()));

edited Nov 30 '21 at 11:23

answered Nov 30 '21 at 11:16

Mureinik

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That's what I thought, but `f.getName()` cannot be resolved! – membersound Nov 30 '21 at 11:16
@membersound see my edited answer – Mureinik Nov 30 '21 at 11:23
You should close the stream returned by `Files.list()`. See [doc](https://docs.oracle.com/en/java/javase/16/docs/api/java.base/java/nio/file/Files.html#list(java.nio.file.Path)) – Nov 30 '21 at 11:35
@sadetaosa but how? – membersound Nov 30 '21 at 12:06
3

`try(Stream files = Files.list(Paths.get(importDir))) { files.sorted(…).forEachOrdered(…); }` – Holger Nov 30 '21 at 12:11
2

Instead of `Comparator. comparing(f -> …)` I’d use `Comparator.comparing((File f) -> …)` – Holger Nov 30 '21 at 12:13

How to sort files in a stream by partial filename?

1 Answers1