pylucene 3.5.0-3

[pylucene.git] / lucene-java-3.5.0 / lucene / src / java / org / apache / lucene / collation / CollationKeyFilter.java

diff --git a/lucene-java-3.5.0/lucene/src/java/org/apache/lucene/collation/CollationKeyFilter.java b/lucene-java-3.5.0/lucene/src/java/org/apache/lucene/collation/CollationKeyFilter.java
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+package org.apache.lucene.collation;
+
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+
+import org.apache.lucene.analysis.TokenFilter;
+import org.apache.lucene.analysis.TokenStream;
+import org.apache.lucene.analysis.tokenattributes.CharTermAttribute;
+import org.apache.lucene.util.IndexableBinaryStringTools;
+
+import java.io.IOException;
+import java.text.Collator;
+
+
+/**
+ * <p>
+ *   Converts each token into its {@link java.text.CollationKey}, and then
+ *   encodes the CollationKey with {@link IndexableBinaryStringTools}, to allow 
+ *   it to be stored as an index term.
+ * </p>
+ * <p>
+ *   <strong>WARNING:</strong> Make sure you use exactly the same Collator at
+ *   index and query time -- CollationKeys are only comparable when produced by
+ *   the same Collator.  Since {@link java.text.RuleBasedCollator}s 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):
+ * </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 Collator#getInstance(java.util.Locale)}.
+ *   </li>
+ *   <li>
+ *     The collation strength used - see {@link Collator#setStrength(int)}
+ *   </li>
+ * </ol> 
+ * <p>
+ *   The <code>ICUCollationKeyFilter</code> in the icu package of Lucene's
+ *   contrib area uses ICU4J's Collator, which makes its
+ *   version available, thus allowing collation to be versioned independently
+ *   from the JVM.  ICUCollationKeyFilter is also significantly faster and
+ *   generates significantly shorter keys than CollationKeyFilter.  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
+ *   java.text.Collator over several languages.
+ * </p>
+ * <p>
+ *   CollationKeys generated by java.text.Collators are not compatible
+ *   with those those generated by ICU Collators.  Specifically, if you use 
+ *   CollationKeyFilter to generate index terms, do not use
+ *   ICUCollationKeyFilter on the query side, or vice versa.
+ * </p>
+ */
+public final class CollationKeyFilter extends TokenFilter {
+  private final Collator collator;
+  private final CharTermAttribute termAtt = addAttribute(CharTermAttribute.class);
+
+  /**
+   * @param input Source token stream
+   * @param collator CollationKey generator
+   */
+  public CollationKeyFilter(TokenStream input, Collator collator) {
+    super(input);
+    // clone in case JRE doesnt properly sync,
+    // or to reduce contention in case they do
+    this.collator = (Collator) collator.clone();
+  }
+
+  @Override
+  public boolean incrementToken() throws IOException {
+    if (input.incrementToken()) {
+      byte[] collationKey = collator.getCollationKey(termAtt.toString()).toByteArray();
+      int encodedLength = IndexableBinaryStringTools.getEncodedLength(
+          collationKey, 0, collationKey.length);
+      termAtt.resizeBuffer(encodedLength);
+      termAtt.setLength(encodedLength);
+      IndexableBinaryStringTools.encode(collationKey, 0, collationKey.length,
+          termAtt.buffer(), 0, encodedLength);
+      return true;
+    } else {
+      return false;
+    }
+  }
+}