http://lucene.apache.org/lucene-parent/lucene-analyzers-common: Additional Analyzers (The Apache Software Foundation) 
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 Unicode collation support.
 

 Collation converts each token into its binary CollationKey 
 using the provided Collator, allowing it to be stored as an index term.
 


Use Cases


    
  
  • 
    Efficient sorting of terms in languages that use non-Unicode character 
    orderings.  (Lucene Sort using a Locale can be very slow.) 
  
    • 
  
  • 
    Efficient range queries over fields that contain terms in languages that 
    use non-Unicode character orderings.  (Range queries using a Locale can be
    very slow.)
  
    • 
  
  •  Effective Locale-specific normalization (case differences, diacritics, etc.). (LowerCaseFilter and ASCIIFoldingFilter provide these services in a generic way that doesn't take into account locale-specific needs.) 
    • 



Example Usages


Farsi Range Queries


  // "fa" Locale is not supported by Sun JDK 1.4 or 1.5
  Collator collator = Collator.getInstance(new Locale("ar"));
  CollationKeyAnalyzer analyzer = new CollationKeyAnalyzer(collator);
  Path dirPath = Files.createTempDirectory("tempIndex");
  Directory dir = FSDirectory.open(dirPath);
  IndexWriter writer = new IndexWriter(dir, new IndexWriterConfig(analyzer));
  Document doc = new Document();
  doc.add(new TextField("content", "\u0633\u0627\u0628", Field.Store.YES));
  writer.addDocument(doc);
  writer.close();
  IndexReader ir = DirectoryReader.open(dir);
  IndexSearcher is = new IndexSearcher(ir);
  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);



Danish Sorting


  Analyzer analyzer 
    = new CollationKeyAnalyzer(Collator.getInstance(new Locale("da", "dk")));
  Path dirPath = Files.createTempDirectory("tempIndex");
  Directory dir = FSDirectory.open(dirPath);
  IndexWriter writer = new IndexWriter(dir, 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 StoredField("tracer", tracer[i]));
    doc.add(new TextField("contents", data[i], Field.Store.NO));
    writer.addDocument(doc);
  }
  writer.close();
  IndexReader ir = DirectoryReader.open(dir);
  IndexSearcher searcher = new IndexSearcher(ir);
  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]);
  }



Turkish Case Normalization


  Collator collator = Collator.getInstance(new Locale("tr", "TR"));
  collator.setStrength(Collator.PRIMARY);
  Analyzer analyzer = new CollationKeyAnalyzer(collator);
  Path dirPath = Files.createTempDirectory("tempIndex");
  Directory dir = FSDirectory.open(dirPath);
  IndexWriter writer = new IndexWriter(dir, new IndexWriterConfig(analyzer));
  Document doc = new Document();
  doc.add(new TextField("contents", "DIGY", Field.Store.NO));
  writer.addDocument(doc);
  writer.close();
  IndexReader ir = DirectoryReader.open(dir);
  IndexSearcher is = new IndexSearcher(ir);
  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);



Caveats and Comparisons



  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):



    
  
  1. JVM vendor
    2. 
  
  2. JVM version, including patch version
    3. 
  
  3.  The language (and country and variant, if specified) of the Locale used when constructing the collator via Collator.getInstance(Locale). 
    4. 
  
  4.  The collation strength used - see Collator.setStrength(int) 
    5. 

 


  ICUCollationKeyAnalyzer, available in the icu analysis module,
  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.



/**
 *  Unicode collation support.
 *  <p>
 *  <code>Collation</code> converts each token into its binary <code>CollationKey</code> 
 *  using the provided <code>Collator</code>, allowing it to be stored as an index term.
 *  </p>
 * 
 * <h2>Use Cases</h2>
 * 
 * <ul>
 *   <li>
 *     Efficient sorting of terms in languages that use non-Unicode character 
 *     orderings.  (Lucene Sort using a Locale can be very slow.) 
 *   </li>
 *   <li>
 *     Efficient range queries over fields that contain terms in languages that 
 *     use non-Unicode character orderings.  (Range queries using a Locale can be
 *     very slow.)
 *   </li>
 *   <li>
 *     Effective Locale-specific normalization (case differences, diacritics, etc.).
 *     ({@link org.apache.lucene.analysis.LowerCaseFilter} and 
 *     {@link org.apache.lucene.analysis.miscellaneous.ASCIIFoldingFilter} provide these services
 *     in a generic way that doesn't take into account locale-specific needs.)
 *   </li>
 * </ul>
 * 
 * <h2>Example Usages</h2>
 * 
 * <h3>Farsi Range Queries</h3>
 * <pre class="prettyprint">
 *   // "fa" Locale is not supported by Sun JDK 1.4 or 1.5
 *   Collator collator = Collator.getInstance(new Locale("ar"));
 *   CollationKeyAnalyzer analyzer = new CollationKeyAnalyzer(collator);
 *   Path dirPath = Files.createTempDirectory("tempIndex");
 *   Directory dir = FSDirectory.open(dirPath);
 *   IndexWriter writer = new IndexWriter(dir, new IndexWriterConfig(analyzer));
 *   Document doc = new Document();
 *   doc.add(new TextField("content", "\u0633\u0627\u0628", Field.Store.YES));
 *   writer.addDocument(doc);
 *   writer.close();
 *   IndexReader ir = DirectoryReader.open(dir);
 *   IndexSearcher is = new IndexSearcher(ir);
 * 
 *   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);
 * </pre>
 * 
 * <h3>Danish Sorting</h3>
 * <pre class="prettyprint">
 *   Analyzer analyzer 
 *     = new CollationKeyAnalyzer(Collator.getInstance(new Locale("da", "dk")));
 *   Path dirPath = Files.createTempDirectory("tempIndex");
 *   Directory dir = FSDirectory.open(dirPath);
 *   IndexWriter writer = new IndexWriter(dir, 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 &lt; data.length ; ++i) {
 *     Document doc = new Document();
 *     doc.add(new StoredField("tracer", tracer[i]));
 *     doc.add(new TextField("contents", data[i], Field.Store.NO));
 *     writer.addDocument(doc);
 *   }
 *   writer.close();
 *   IndexReader ir = DirectoryReader.open(dir);
 *   IndexSearcher searcher = new IndexSearcher(ir);
 *   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 &lt; result.length ; ++i) {
 *     Document doc = searcher.doc(result[i].doc);
 *     assertEquals(sortedTracerOrder[i], doc.getValues("tracer")[0]);
 *   }
 * </pre>
 * 
 * <h3>Turkish Case Normalization</h3>
 * <pre class="prettyprint">
 *   Collator collator = Collator.getInstance(new Locale("tr", "TR"));
 *   collator.setStrength(Collator.PRIMARY);
 *   Analyzer analyzer = new CollationKeyAnalyzer(collator);
 *   Path dirPath = Files.createTempDirectory("tempIndex");
 *   Directory dir = FSDirectory.open(dirPath);
 *   IndexWriter writer = new IndexWriter(dir, new IndexWriterConfig(analyzer));
 *   Document doc = new Document();
 *   doc.add(new TextField("contents", "DIGY", Field.Store.NO));
 *   writer.addDocument(doc);
 *   writer.close();
 *   IndexReader ir = DirectoryReader.open(dir);
 *   IndexSearcher is = new IndexSearcher(ir);
 *   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);
 * </pre>
 * 
 * <h2>Caveats and Comparisons</h2>
 * <p>
 *   <strong>WARNING:</strong> Make sure you use exactly the same 
 *   <code>Collator</code> at index and query time -- <code>CollationKey</code>s
 *   are only comparable when produced by
 *   the same <code>Collator</code>.  Since {@link java.text.RuleBasedCollator}s
 *   are not independently versioned, it is unsafe to search against stored
 *   <code>CollationKey</code>s 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):
 * </p>
 * <ol>
 *   <li>JVM vendor</li>
 *   <li>JVM version, including patch version</li>
 *   <li>
 *     The language (and country and variant, if specified) of the Locale
 *     used when constructing the collator via
 *     {@link java.text.Collator#getInstance(java.util.Locale)}.
 *   </li>
 *   <li>
 *     The collation strength used - see {@link java.text.Collator#setStrength(int)}
 *   </li>
 * </ol> 
 * <p>
 *   <code>ICUCollationKeyAnalyzer</code>, available in the <a href="{@docRoot}/../analyzers-icu/overview-summary.html">icu analysis module</a>,
 *   uses ICU4J's <code>Collator</code>, which 
 *   makes its version available, thus allowing collation to be versioned
 *   independently from the JVM.  <code>ICUCollationKeyAnalyzer</code> is also 
 *   significantly faster and generates significantly shorter keys than 
 *   <code>CollationKeyAnalyzer</code>.  See
 *   <a href="http://site.icu-project.org/charts/collation-icu4j-sun"
 *     >http://site.icu-project.org/charts/collation-icu4j-sun</a> for key
 *   generation timing and key length comparisons between ICU4J and
 *   <code>java.text.Collator</code> over several languages.
 * </p>
 * <p>
 *   <code>CollationKey</code>s generated by <code>java.text.Collator</code>s are 
 *   not compatible with those those generated by ICU Collators.  Specifically, if
 *   you use <code>CollationKeyAnalyzer</code> to generate index terms, do not use
 *   <code>ICUCollationKeyAnalyzer</code> on the query side, or vice versa.
 * </p>
 */
package org.apache.lucene.collation;