Supply a ReverseFileReader
--------------------------
Key: IO-288
URL: https://issues.apache.org/jira/browse/IO-288
Project: Commons IO
Issue Type: New Feature
Components: Utilities
Reporter: Georg Henzler
Attachments: ReverseFileReader.java
I needed to analyse a log file today and I was looking for a ReverseFileReader:
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 is 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 follows:
int blockSize = 4096; // only that much memory is needed, no matter how big the
file is
ReverseFileReader reverseFileReader = new ReverseFileReader(myFile, blockSize,
"UTF-8");
String line = null;
while((line=reverseFileReader.readLine())!=null) {
... // use the line
if(enoughLinesSeen) {
break;
}
}
reverseFileReader.close();
I believe this could be useful for other people as well!
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