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From "Jukka Zitting (JIRA)" <j...@apache.org>
Subject [jira] Commented: (TIKA-171) New ContentHandler for plain text output that has no problem with missing white space after XHTML block tags
Date Fri, 28 Nov 2008 01:04:44 GMT

    [ https://issues.apache.org/jira/browse/TIKA-171?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12651443#action_12651443

Jukka Zitting commented on TIKA-171:

Good idea!

Patch committed in revision 721317. Note that I changed the indenting to use spaces instead
of tabs to match the normal practice in Tika.

Your code also doesn't comply with the Sun Java coding conventions we follow (most notably
the if statements should always use braces)
but for now I left the code as-is to avoid conflicts in case you already made some local changes.

We already do something similar in a number of the parsers that explicitly output extra whitespace
like newlines and tabs at suitable places to make the test output look better. This generic
approach is IMHO better, and so we should remove such per-parser code.

Instead of having XHTMLToTextContentHandler pass through only character events, how about
if it passed all SAX events and simply inserted extra ignorableWhitespace events where appropriate?
This would make the different features more orthogonal and thus easier to combine in new ways.
The current functionality could still be achieved by combining the class with TextContentHandler
or WriteOutContentHandler.

Some other potential improvements:

* Emit a double newline at the end of block elements (but only a single newline after </tr>
or <br/>) to produce an empty line to separate paragraphs in text output. This makes
the output easier for manual inspection and might even help some post-processors (that for
some reason don't know how to use XHTML) to better detect structure in the text output.

* Detect if the incoming XHTML document already has such extra whitespace and either (partially)
replace it with the emitted whitespace or keep it and avoid emitting extra whitespace.

* Avoid emitting extra whitespace for empty elements. This way we can keep the nicely symmetric
property that an empty input stream results in an empty text output stream.

Anyway, these are all minor tweaks and we probably shouldn't spend too much effort tweaking
the output. The main purpose of the text output is just to be indexable so even the current
implementation is perfectly OK. Nice text rendering is only a secondary concern.

> New ContentHandler for plain text output that has no problem with missing white space
after XHTML block tags
> ------------------------------------------------------------------------------------------------------------
>                 Key: TIKA-171
>                 URL: https://issues.apache.org/jira/browse/TIKA-171
>             Project: Tika
>          Issue Type: Improvement
>          Components: general
>    Affects Versions: 0.2
>            Reporter: Uwe Schindler
>         Attachments: TIKA-171.patch
> One problem with mapping document content to plain text is incorrect whitespace handling:
> The normal way to parse documents to plain text is to instantiate a parser and pass the
SAX events from the parser to a BodyContentHandler(TextContentHandler(Writer)). This appends
all output to a writer (see example on web site).
> This works good for thumb parsers that just create a single <p>> tag in XHTML
output whith all content of the document in it (including newlines).
> As soon, as a more inteligent parser is used (e.g. HTML Parser) that creates multiple
nodes and a feature-rich XHTML document, the problems begin. The TextContentHandler just strips
all tags away and only characters() events are forwarded to the Writer. When the original
document (e.g. a HTML document) does not contain additional whitespace and linefeeds (e.g.
it is correct and possible to create a XHTML document with all content in one text line, but
consisting of several paragraphs. In this case </p><p> events between paragraphs
are stripped and there is no whitespace anymore between the two paragraphs.
> My patch contains a new XHTMLToTextContentHandler, that checks the elements and inserts
whitespace to the output depending on the XHTML tag type. HTML block tags like <p/>
get a newline at the end, but HTML inline tags do not add whitespace. This mapping is done
by a simple Set<String> of tag names extracted from the XHTML 1.0 spec. To make it even
better, tables are printed out with white space and tabs between cells.
> With this patch, I am able to correctly index a lot of document with Lucene.
> The patch also changes some tests to correctly check for the '\n' at the end of plain
text streams (which are included because of the single <p>-paragraph around plain text).

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