A java 8 stream that maps and collects all except the first item

Question

I have a file format for potentially large files where the first line is special. I'd like to open the file once and treat it as a stream of lines, but handle the first line differently from all of the other lines. The others get map/collected, the first line needs to be just parsed into some flags. Is there a way?

This starts as:

result = Files.lines(path).map(something).collect(Collectors.toList());

except that I want to divert the first line.

http://stackoverflow.com/a/34640360/2711488 – Holger May 12 '16 at 09:10 — Holger, May 12 '16 at 09:10

score 9 · Accepted Answer · answered May 11 '16 at 17:42

9

If you must only open the file once, the easiest thing to do is to make a BufferedReader, get the first line and then stream over the rest:

BufferedReader reader = Files.newBufferedReader(path);

String firstLine = reader.readLine();

result = reader.lines()
    .map(something)
    .collect(toList());

answered May 11 '16 at 17:42

Misha

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Note that, unlike `Files.lines()`, the `Stream` returned by `BufferedReader.lines()` does not close the file when `close()` is called on the `Stream`. – Hank D May 11 '16 at 17:50
3

@HankD Right, `reader` should be set up in try-with-resources block. – Misha May 11 '16 at 17:54
Thank you; this rather nice idea eluded me. – bmargulies May 11 '16 at 18:02

A java 8 stream that maps and collects all except the first item

1 Answers1