[jira] [Commented] (CSV-131) Save positions of records to enable random access

["Adrian Crum (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CSV-131?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14188076#comment-14188076 ] 

Adrian Crum commented on CSV-131:
---------------------------------

It seems to me this could be made a bit more elegant if the random access feature was implemented as a decorator. Something like:

{code}
RandomAccessParser rap = new RandomAccessParser (parser, ...);
// Do random access stuff with rap
{code}


> Save positions of records to enable random access
> -------------------------------------------------
>
>                 Key: CSV-131
>                 URL: https://issues.apache.org/jira/browse/CSV-131
>             Project: Commons CSV
>          Issue Type: Improvement
>          Components: Parser
>    Affects Versions: 1.1
>            Reporter: Holger Stratmann
>            Priority: Minor
>         Attachments: CSV-131-gg-0.diff, PositionTrackingFull_v101_20140910.patch, PositionTrackingTest_20140907.patch, PositionTracking_20140907.patch, ggregory-CSV-131-parser-and-record.diff
>
>   Original Estimate: 1h
>  Remaining Estimate: 1h
>
> It would be good to have {{CSVRecord}} save its position in the source stream.
> Reason: Knowing the position of the records would enable random access to retrieve records from the source (after reading it once to build an index) if the file is too large to be read into memory (or if we don't want to read the full file to access a record in the middle).
> Additional info: I have created a "random access csv reader" and a "csv viewer" (Swing) for arbitrarily large CSV files. It requires one additional scan of the file to build an index (multi-byte charsets supported). The index can be saved to a file so it only needs to be built once. Because the lexer uses a BufferedReader, we need "internal information" to know where each record starts.
> The change to "core" is minor: one field in {{CSVRecord}}s and some associated methods to store the position.
> Patch will be attached.
> Code for random access (both UI and non-UI) will be proposed (and possibly submitted) as a separate issue. It could also be an independent add-on but requires this one little change to Commons CSV.



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