Use lambda to filter Reader

Question

I'm reading lines from a zipped input stream, and I need to filter it by the first 4 positions (a period). Is is possible to use a lambda (like the filter in streams) to avoid the condition?

private List<String> readlinesByPeriod(DPeriod period, ZipInputStream zis) throws IOException {
    List<String> lines = new ArrayList();

    byte[] data = SCIOUtils.readData(zis);
    InputStream is = new ByteArrayInputStream(data);
    BufferedReader reader = new BufferedReader(new InputStreamReader(is, CharEncoding.ISO_8859_1));
    String line;
    while ((line = reader.readLine()) != null) {
        String periodCode = StringUtils.substring(line, 0, 4);
        if (periodCode.equals(period.getCode())) {
            lines.add(line);
        }
    }

    return lines;
}

Michael · Accepted Answer · 2021-11-25 12:15:53Z

1

Yes, it's possible

return reader.lines()
    .filter(line -> StringUtils.substring(line, 0, 4).equals(period.getCode()))
    .collect(Collectors.toList());

It's worth noting that the JavaDoc for BufferedReader.lines says

If an IOException is thrown when accessing the underlying BufferedReader, it is wrapped in an UncheckedIOException which will be thrown from the Stream method that caused the read to take place

So if you want your method to continue to throw a checked exception (IOException or otherwise), then you'd have to wrap the above in a try-catch block for UncheckedIOException and wrap it and rethrow as a checked exception.

edited Nov 25, 2021 at 12:15

answered Nov 25, 2021 at 12:05

Michael

44.5k12 gold badges98 silver badges143 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Lluis Martinez Over a year ago

I found that BufferedReader has a lines method which returns a Stream, I used: return reader.lines() .filter(line -> line.startsWith(period.getCode())) .collect(Collectors.toList());

Michael Over a year ago

@LluisMartinez Oh, good find. I learned something today. I didn't think they'd bothered to retrospectively add stream support to classes like BufferedReader. Updated my answer

Collectives™ on Stack Overflow

Use lambda to filter Reader

1 Answer 1

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related