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From "Georg Henzler (Updated) (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (IO-288) Supply a ReverseFileReader
Date Tue, 18 Oct 2011 22:35:10 GMT

     [ https://issues.apache.org/jira/browse/IO-288?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Georg Henzler updated IO-288:
-----------------------------

    Attachment: ReverseFileReader.java

Sorry, I didn't notice the radio buttons when I first uploaded...
                
> 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 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
> ReverseFileReader reverseFileReader = new ReverseFileReader(myFile, blockSize, "UTF-8");
// encoding is supported
> 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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