[Jackrabbit Wiki] Update of "SpellChecker" by MarcelReutegger

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The following page has been changed by MarcelReutegger:
http://wiki.apache.org/jackrabbit/SpellChecker

New page:
The lucene based query handler implementation supports a pluggable spell checker mechanism. Per default spell checking is not available and you have to configure it first. See parameter {{{spellCheckerClass}}} on page ["Search"]. Jackrabbit currently provides an implementation in the sandbox area, which uses the [http://wiki.apache.org/jakarta-lucene/SpellChecker lucene-spellchecker] contrib. The dictionary is derived from the fulltext indexed content of the workspace and updated periodically. You can configure the refresh interval by picking one of the available inner classes of {{{org.apache.jackrabbit.core.query.lucene.spell.LuceneSpellChecker}}}:

 * One``Minute``Refresh``Interval
 * Five``Minutes``Refresh``Interval
 * Thirty``Minutes``Refresh``Interval
 * One``Hour``Refresh``Interval
 * Six``Hours``Refresh``Interval
 * Twelve``Hours``Refresh``Interval
 * One``Day``Refresh``Interval

E.g. if you want a refresh interval of six hours the class name is: {{{org.apache.jackrabbit.core.query.lucene.spell.LuceneSpellChecker$SixHoursRefreshInterval}}}. If you use {{{org.apache.jackrabbit.core.query.lucene.spell.LuceneSpellChecker}}} the refresh interval will be one hour.

The spell checker dictionary is stored as a lucene index under <workspace-name>/index/spellchecker. If it does not exist, a background thread will create it on startup. Similarly the dictionary refresh is also done in a background thread to not block regular queries.

== How do I use it? ==

You can spell check a fulltext statement either with an XPath or a SQL query:

{{{
    // rep:spellcheck('jackrabit') will always evaluate to true
    Query query = qm.createQuery("/jcr:root[rep:spellcheck('jackrabit')]/(rep:spellcheck())", Query.XPATH);
    RowIterator rows = query.execute().getRows();
    // the above query will always return the root node no matter what string we check
    Row r = rows.nextRow();
    // get the result of the spell checking
    Value v = r.getValue("rep:spellcheck()");
    if (v == null) {
        // no suggestion returned, the spelling is correct or the spell checker
        // does not know how to correct it.
    } else {
        String suggestion = v.getString();
    }
}}}

And the same using SQL:

{{{
    // SPELLCHECK('jackrabit') will always evaluate to true
    Query query = qm.createQuery("SELECT rep:spellcheck() FROM nt:base WHERE jcr:path = '/' AND SPELLCHECK('jackrabit')", Query.SQL);
    RowIterator rows = query.execute().getRows();
    // the above query will always return the root node no matter what string we check
    Row r = rows.nextRow();
    // get the result of the spell checking
    Value v = r.getValue("rep:spellcheck()");
    if (v == null) {
        // no suggestion returned, the spelling is correct or the spell checker
        // does not know how to correct it.
    } else {
        String suggestion = v.getString();
    }
}}}