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https://issues.apache.org/jira/browse/IO-288?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13150294#comment-13150294
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Georg Henzler commented on IO-288:
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Sorry for the spurious files, i created the zip with the default utility in
OS-X.
I think the code addresses most of your questions already:
- There are a few tests already (testXxxxSmallBlockSize()) that test the
multi-block behaviour for lines that span a block (you can go down to a block
size of 1 and it still works, that shows that the algorithm is solid I think)
- I think it's clever to encode the newline characters - that way we
automatically get the correct byte sequence for multi byte encodings (e.g.
UTF-16) and if a one byte-per-char-encoding chose to use different bytes it
would also work (performance is no issue for this as it happens only once)
- I think about getNewLineMatchByteCount() to make it more efficient - although
for the standard ISO case it ends up just being four byte comparisons instead
of three. Should make almost no difference but on the pro side it makes the
implementation nicely generic.
- It's true, there is an issue with block-spanning newlines to be fixed. If a
windows newline (\r\n) happens to span a block a wrong extra empty line will be
returned.
I'll provide a fix for the newline problem and will change totalBlockCount to
long.
> Supply a ReversedLinesFileReader
> ---------------------------------
>
> Key: IO-288
> URL: https://issues.apache.org/jira/browse/IO-288
> Project: Commons IO
> Issue Type: New Feature
> Components: Utilities
> Reporter: Georg Henzler
> Fix For: 2.2
>
> Attachments: ReversedLinesFileReader0.2.zip
>
>
> I needed to analyse a log file today and I was looking for a
> ReversedLinesFileReader: A class that behaves exactly like BufferedReader
> except that it goes from bottom to top when readLine() is called. I didn't
> find it in IOUtils and the internet didn't help a lot either, e.g.
> http://www.java2s.com/Tutorial/Java/0180__File/ReversingaFile.htm is a fairly
> inefficient - the log files I'm analysing are huge and it is not a good idea
> to load the whole content in the memory.
> So I ended up writing an implementation myself using little memory and the
> class RandomAccessFile - see attached file. It's used as follows:
> int blockSize = 4096; // only that much memory is needed, no matter how big
> the file is
> ReversedLinesFileReader reversedLinesFileReader = new ReversedLinesFileReader
> (myFile, blockSize, "UTF-8"); // encoding is supported
> String line = null;
> while((line=reversedLinesFileReader.readLine())!=null) {
> ... // use the line
> if(enoughLinesSeen) {
> break;
> }
> }
> reversedLinesFileReader.close();
> I believe this could be useful for other people as well!
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