See: Description
| Package | Description |
|---|---|
| org.apache.lucene.analysis.icu |
Analysis components based on ICU
|
| org.apache.lucene.analysis.icu.segmentation |
Tokenizer that breaks text into words with the Unicode Text Segmentation algorithm.
|
| org.apache.lucene.analysis.icu.tokenattributes |
Additional ICU-specific Attributes for text analysis.
|
| org.apache.lucene.collation |
Unicode Collation support.
|
| org.apache.lucene.collation.tokenattributes |
Custom
AttributeImpl for indexing collation keys as index terms. |
This module exposes functionality from ICU to Apache Lucene. ICU4J is a Java library that enhances Java's internationalization support by improving performance, keeping current with the Unicode Standard, and providing richer APIs.
For an introduction to Lucene's analysis API, see the org.apache.lucene.analysis package documentation.
This module exposes the following functionality:
Text Segmentation (Tokenization) divides document and query text into index terms (typically words). Unicode provides special properties and rules so that this can be done in a manner that works well with most languages.
Text Segmentation implements the word segmentation specified in Unicode Text Segmentation. Additionally the algorithm can be tailored based on writing system, for example text in the Thai script is automatically delegated to a dictionary-based segmentation algorithm.
/** * This tokenizer will work well in general for most languages. */ Tokenizer tokenizer = new ICUTokenizer(reader);
ICUCollationKeyAnalyzer
converts each token into its binary CollationKey using the
provided Collator, allowing it to be
stored as an index term.
ICUCollationKeyAnalyzer depends on ICU4J to produce the
CollationKeys.
LowerCaseFilter and
ASCIIFoldingFilter provide these services
in a generic way that doesn't take into account locale-specific needs.)
Collator collator = Collator.getInstance(new ULocale("ar"));
ICUCollationKeyAnalyzer analyzer = new ICUCollationKeyAnalyzer(collator);
RAMDirectory ramDir = new RAMDirectory();
IndexWriter writer = new IndexWriter(ramDir, new IndexWriterConfig(analyzer));
Document doc = new Document();
doc.add(new Field("content", "\u0633\u0627\u0628",
Field.Store.YES, Field.Index.ANALYZED));
writer.addDocument(doc);
writer.close();
IndexSearcher is = new IndexSearcher(ramDir, true);
QueryParser aqp = new QueryParser("content", analyzer);
aqp.setAnalyzeRangeTerms(true);
// Unicode order would include U+0633 in [ U+062F - U+0698 ], but Farsi
// orders the U+0698 character before the U+0633 character, so the single
// indexed Term above should NOT be returned by a ConstantScoreRangeQuery
// with a Farsi Collator (or an Arabic one for the case when Farsi is not
// supported).
ScoreDoc[] result
= is.search(aqp.parse("[ \u062F TO \u0698 ]"), null, 1000).scoreDocs;
assertEquals("The index Term should not be included.", 0, result.length);
Analyzer analyzer
= new ICUCollationKeyAnalyzer(Collator.getInstance(new ULocale("da", "dk")));
RAMDirectory indexStore = new RAMDirectory();
IndexWriter writer = new IndexWriter(indexStore, new IndexWriterConfig(analyzer));
String[] tracer = new String[] { "A", "B", "C", "D", "E" };
String[] data = new String[] { "HAT", "HUT", "H\u00C5T", "H\u00D8T", "HOT" };
String[] sortedTracerOrder = new String[] { "A", "E", "B", "D", "C" };
for (int i = 0 ; i < data.length ; ++i) {
Document doc = new Document();
doc.add(new Field("tracer", tracer[i], Field.Store.YES, Field.Index.NO));
doc.add(new Field("contents", data[i], Field.Store.NO, Field.Index.ANALYZED));
writer.addDocument(doc);
}
writer.close();
IndexSearcher searcher = new IndexSearcher(indexStore, true);
Sort sort = new Sort();
sort.setSort(new SortField("contents", SortField.STRING));
Query query = new MatchAllDocsQuery();
ScoreDoc[] result = searcher.search(query, null, 1000, sort).scoreDocs;
for (int i = 0 ; i < result.length ; ++i) {
Document doc = searcher.doc(result[i].doc);
assertEquals(sortedTracerOrder[i], doc.getValues("tracer")[0]);
}
Collator collator = Collator.getInstance(new ULocale("tr", "TR"));
collator.setStrength(Collator.PRIMARY);
Analyzer analyzer = new ICUCollationKeyAnalyzer(collator);
RAMDirectory ramDir = new RAMDirectory();
IndexWriter writer = new IndexWriter(ramDir, new IndexWriterConfig(analyzer));
Document doc = new Document();
doc.add(new Field("contents", "DIGY", Field.Store.NO, Field.Index.ANALYZED));
writer.addDocument(doc);
writer.close();
IndexSearcher is = new IndexSearcher(ramDir, true);
QueryParser parser = new QueryParser("contents", analyzer);
Query query = parser.parse("d\u0131gy"); // U+0131: dotless i
ScoreDoc[] result = is.search(query, null, 1000).scoreDocs;
assertEquals("The index Term should be included.", 1, result.length);
WARNING: Make sure you use exactly the same
Collator at index and query time -- CollationKeys
are only comparable when produced by
the same Collator. Since RuleBasedCollators
are not independently versioned, it is unsafe to search against stored
CollationKeys unless the following are exactly the same (best
practice is to store this information with the index and check that they
remain the same at query time):
Collator.getInstance(java.util.Locale).
Collator.setStrength(int)
ICUCollationKeyAnalyzer uses ICU4J's Collator, which
makes its version available, thus allowing collation to be versioned
independently from the JVM. ICUCollationKeyAnalyzer is also
significantly faster and generates significantly shorter keys than
CollationKeyAnalyzer. See
http://site.icu-project.org/charts/collation-icu4j-sun for key
generation timing and key length comparisons between ICU4J and
java.text.Collator over several languages.
CollationKeys generated by java.text.Collators are
not compatible with those those generated by ICU Collators. Specifically, if
you use CollationKeyAnalyzer to generate index terms, do not use
ICUCollationKeyAnalyzer on the query side, or vice versa.
ICUNormalizer2Filter normalizes term text to a
Unicode Normalization Form, so
that equivalent
forms are standardized to a unique form.
/** * Normalizer2 objects are unmodifiable and immutable. */ Normalizer2 normalizer = Normalizer2.getInstance(null, "nfc", Normalizer2.Mode.COMPOSE); /** * This filter will normalize to NFC. */ TokenStream tokenstream = new ICUNormalizer2Filter(tokenizer, normalizer);
Default caseless matching, or case-folding is more than just conversion to lowercase. For example, it handles cases such as the Greek sigma, so that "Μάϊος" and "ΜΆΪΟΣ" will match correctly.
Case-folding is still only an approximation of the language-specific rules governing case. If the specific language is known, consider using ICUCollationKeyFilter and indexing collation keys instead. This implementation performs the "full" case-folding specified in the Unicode standard, and this may change the length of the term. For example, the German ß is case-folded to the string 'ss'.
Case folding is related to normalization, and as such is coupled with it in this integration. To perform case-folding, you use normalization with the form "nfkc_cf" (which is the default).
/** * This filter will case-fold and normalize to NFKC. */ TokenStream tokenstream = new ICUNormalizer2Filter(tokenizer);
Search term folding removes distinctions (such as accent marks) between similar characters. It is useful for a fuzzy or loose search.
Search term folding implements many of the foldings specified in Character Foldings as a special normalization form. This folding applies NFKC, Case Folding, and many character foldings recursively.
/** * This filter will case-fold, remove accents and other distinctions, and * normalize to NFKC. */ TokenStream tokenstream = new ICUFoldingFilter(tokenizer);
ICU provides text-transformation functionality via its Transliteration API. This allows you to transform text in a variety of ways, taking context into account.
For more information, see the User's Guide and Rule Tutorial.
/**
* This filter will map Traditional Chinese to Simplified Chinese
*/
TokenStream tokenstream = new ICUTransformFilter(tokenizer, Transliterator.getInstance("Traditional-Simplified"));
/**
* This filter will map Serbian Cyrillic to Serbian Latin according to BGN rules
*/
TokenStream tokenstream = new ICUTransformFilter(tokenizer, Transliterator.getInstance("Serbian-Latin/BGN"));
This module exists to provide up-to-date Unicode functionality that supports
the most recent version of Unicode (currently 6.3). However, some users who wish
for stronger backwards compatibility can restrict
ICUNormalizer2Filter to operate on only
a specific Unicode Version by using a FilteredNormalizer2.
/**
* This filter will do NFC normalization, but will ignore any characters that
* did not exist as of Unicode 5.0. Because of the normalization stability policy
* of Unicode, this is an easy way to force normalization to a specific version.
*/
Normalizer2 normalizer = Normalizer2.getInstance(null, "nfc", Normalizer2.Mode.COMPOSE);
UnicodeSet set = new UnicodeSet("[:age=5.0:]");
// see FilteredNormalizer2 docs, the set should be frozen or performance will suffer
set.freeze();
FilteredNormalizer2 unicode50 = new FilteredNormalizer2(normalizer, set);
TokenStream tokenstream = new ICUNormalizer2Filter(tokenizer, unicode50);
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