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Lucene example source code file (Analyzer.java)

This example Lucene source code file (Analyzer.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Lucene tags/keywords

alreadyclosedexception, alreadyclosedexception, analyzer, analyzer, class, closeable, closeablethreadlocal, io, ioexception, nullpointerexception, object, reader, reader, reflection, tokenstream, tokenstream

The Lucene Analyzer.java source code

package org.apache.lucene.analysis;

/**
 * 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 java.io.Reader;
import java.io.IOException;
import java.io.Closeable;
import java.lang.reflect.Modifier;

import org.apache.lucene.util.CloseableThreadLocal;
import org.apache.lucene.store.AlreadyClosedException;

import org.apache.lucene.document.Fieldable;

/** An Analyzer builds TokenStreams, which analyze text.  It thus represents a
 *  policy for extracting index terms from text.
 *  <p>
 *  Typical implementations first build a Tokenizer, which breaks the stream of
 *  characters from the Reader into raw Tokens.  One or more TokenFilters may
 *  then be applied to the output of the Tokenizer.
 * <p>The {@code Analyzer}-API in Lucene is based on the decorator pattern.
 * Therefore all non-abstract subclasses must be final or their {@link #tokenStream}
 * and {@link #reusableTokenStream} implementations must be final! This is checked
 * when Java assertions are enabled.
 */
public abstract class Analyzer implements Closeable {

  protected Analyzer() {
    super();
    assert assertFinal();
  }
  
  private boolean assertFinal() {
    try {
      final Class<?> clazz = getClass();
      assert clazz.isAnonymousClass() ||
        (clazz.getModifiers() & (Modifier.FINAL | Modifier.PRIVATE)) != 0 ||
        (
          Modifier.isFinal(clazz.getMethod("tokenStream", String.class, Reader.class).getModifiers()) &&
          Modifier.isFinal(clazz.getMethod("reusableTokenStream", String.class, Reader.class).getModifiers())
        ) :
        "Analyzer implementation classes or at least their tokenStream() and reusableTokenStream() implementations must be final";
      return true;
    } catch (NoSuchMethodException nsme) {
      return false;
    }
  }

  /** Creates a TokenStream which tokenizes all the text in the provided
   * Reader.  Must be able to handle null field name for
   * backward compatibility.
   */
  public abstract TokenStream tokenStream(String fieldName, Reader reader);

  /** Creates a TokenStream that is allowed to be re-used
   *  from the previous time that the same thread called
   *  this method.  Callers that do not need to use more
   *  than one TokenStream at the same time from this
   *  analyzer should use this method for better
   *  performance.
   */
  public TokenStream reusableTokenStream(String fieldName, Reader reader) throws IOException {
    return tokenStream(fieldName, reader);
  }

  private CloseableThreadLocal<Object> tokenStreams = new CloseableThreadLocal();

  /** Used by Analyzers that implement reusableTokenStream
   *  to retrieve previously saved TokenStreams for re-use
   *  by the same thread. */
  protected Object getPreviousTokenStream() {
    try {
      return tokenStreams.get();
    } catch (NullPointerException npe) {
      if (tokenStreams == null) {
        throw new AlreadyClosedException("this Analyzer is closed");
      } else {
        throw npe;
      }
    }
  }

  /** Used by Analyzers that implement reusableTokenStream
   *  to save a TokenStream for later re-use by the same
   *  thread. */
  protected void setPreviousTokenStream(Object obj) {
    try {
      tokenStreams.set(obj);
    } catch (NullPointerException npe) {
      if (tokenStreams == null) {
        throw new AlreadyClosedException("this Analyzer is closed");
      } else {
        throw npe;
      }
    }
  }

  /**
   * Invoked before indexing a Fieldable instance if
   * terms have already been added to that field.  This allows custom
   * analyzers to place an automatic position increment gap between
   * Fieldable instances using the same field name.  The default value
   * position increment gap is 0.  With a 0 position increment gap and
   * the typical default token position increment of 1, all terms in a field,
   * including across Fieldable instances, are in successive positions, allowing
   * exact PhraseQuery matches, for instance, across Fieldable instance boundaries.
   *
   * @param fieldName Fieldable name being indexed.
   * @return position increment gap, added to the next token emitted from {@link #tokenStream(String,Reader)}
   */
  public int getPositionIncrementGap(String fieldName) {
    return 0;
  }

  /**
   * Just like {@link #getPositionIncrementGap}, except for
   * Token offsets instead.  By default this returns 1 for
   * tokenized fields and, as if the fields were joined
   * with an extra space character, and 0 for un-tokenized
   * fields.  This method is only called if the field
   * produced at least one token for indexing.
   *
   * @param field the field just indexed
   * @return offset gap, added to the next token emitted from {@link #tokenStream(String,Reader)}
   */
  public int getOffsetGap(Fieldable field) {
    if (field.isTokenized())
      return 1;
    else
      return 0;
  }

  /** Frees persistent resources used by this Analyzer */
  public void close() {
    tokenStreams.close();
    tokenStreams = null;
  }
}

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