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Lucene example source code file (CharacterUtils.java)

This example Lucene source code file (CharacterUtils.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

characterbuffer, characterbuffer, characterutils, characterutils, charsequence, io, ioexception, java4characterutils, java5characterutils, java5characterutils, java_4, java_5, override, override, reader

The Lucene CharacterUtils.java source code

package org.apache.lucene.util;

import java.io.IOException;
import java.io.Reader;

/**
 * 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.
 */

/**
 * {@link CharacterUtils} provides a unified interface to Character-related
 * operations to implement backwards compatible character operations based on a
 * {@link Version} instance.
 * 
 * @lucene.internal
 */
public abstract class CharacterUtils {
  private static final Java4CharacterUtils JAVA_4 = new Java4CharacterUtils();
  private static final Java5CharacterUtils JAVA_5 = new Java5CharacterUtils();

  /**
   * Returns a {@link CharacterUtils} implementation according to the given
   * {@link Version} instance.
   * 
   * @param matchVersion
   *          a version instance
   * @return a {@link CharacterUtils} implementation according to the given
   *         {@link Version} instance.
   */
  public static CharacterUtils getInstance(final Version matchVersion) {
    return matchVersion.onOrAfter(Version.LUCENE_31) ? JAVA_5 : JAVA_4;
  }

  /**
   * Returns the code point at the given index of the char array.
   * Depending on the {@link Version} passed to
   * {@link CharacterUtils#getInstance(Version)} this method mimics the behavior
   * of {@link Character#codePointAt(char[], int)} as it would have been
   * available on a Java 1.4 JVM or on a later virtual machine version.
   * 
   * @param chars
   *          a character array
   * @param offset
   *          the offset to the char values in the chars array to be converted
   * 
   * @return the Unicode code point at the given index
   * @throws NullPointerException
   *           - if the array is null.
   * @throws IndexOutOfBoundsException
   *           - if the value offset is negative or not less than the length of
   *           the char array.
   */
  public abstract int codePointAt(final char[] chars, final int offset);

  /**
   * Returns the code point at the given index of the {@link CharSequence}.
   * Depending on the {@link Version} passed to
   * {@link CharacterUtils#getInstance(Version)} this method mimics the behavior
   * of {@link Character#codePointAt(char[], int)} as it would have been
   * available on a Java 1.4 JVM or on a later virtual machine version.
   * 
   * @param seq
   *          a character sequence
   * @param offset
   *          the offset to the char values in the chars array to be converted
   * 
   * @return the Unicode code point at the given index
   * @throws NullPointerException
   *           - if the sequence is null.
   * @throws IndexOutOfBoundsException
   *           - if the value offset is negative or not less than the length of
   *           the character sequence.
   */
  public abstract int codePointAt(final CharSequence seq, final int offset);
  
  /**
   * Returns the code point at the given index of the char array where only elements
   * with index less than the limit are used.
   * Depending on the {@link Version} passed to
   * {@link CharacterUtils#getInstance(Version)} this method mimics the behavior
   * of {@link Character#codePointAt(char[], int)} as it would have been
   * available on a Java 1.4 JVM or on a later virtual machine version.
   * 
   * @param chars
   *          a character array
   * @param offset
   *          the offset to the char values in the chars array to be converted
   * @param limit the index afer the last element that should be used to calculate
   *        codepoint.  
   * 
   * @return the Unicode code point at the given index
   * @throws NullPointerException
   *           - if the array is null.
   * @throws IndexOutOfBoundsException
   *           - if the value offset is negative or not less than the length of
   *           the char array.
   */
  public abstract int codePointAt(final char[] chars, final int offset, final int limit);
  
  /**
   * Creates a new {@link CharacterBuffer} and allocates a <code>char[]
   * of the given bufferSize.
   * 
   * @param bufferSize
   *          the internal char buffer size, must be <code>>= 2
   * @return a new {@link CharacterBuffer} instance.
   */
  public static CharacterBuffer newCharacterBuffer(final int bufferSize) {
    if(bufferSize < 2)
      throw new IllegalArgumentException("buffersize must be >= 2");
    return new CharacterBuffer(new char[bufferSize], 0, 0);
  }

  /**
   * Fills the {@link CharacterBuffer} with characters read from the given
   * reader {@link Reader}. This method tries to read as many characters into
   * the {@link CharacterBuffer} as possible, each call to fill will start
   * filling the buffer from offset <code>0 up to the length of the size
   * of the internal character array.
   * <p>
   * Depending on the {@link Version} passed to
   * {@link CharacterUtils#getInstance(Version)} this method implements
   * supplementary character awareness when filling the given buffer. For all
   * {@link Version} > 3.0 {@link #fill(CharacterBuffer, Reader)} guarantees
   * that the given {@link CharacterBuffer} will never contain a high surrogate
   * character as the last element in the buffer unless it is the last available
   * character in the reader. In other words, high and low surrogate pairs will
   * always be preserved across buffer boarders.
   * </p>
   * 
   * @param buffer
   *          the buffer to fill.
   * @param reader
   *          the reader to read characters from.
   * @return <code>true if and only if no more characters are available
   *         in the reader, otherwise <code>false.
   * @throws IOException
   *           if the reader throws an {@link IOException}.
   */
  public abstract boolean fill(CharacterBuffer buffer, Reader reader) throws IOException;

  private static final class Java5CharacterUtils extends CharacterUtils {
    Java5CharacterUtils() {
    }

    @Override
    public final int codePointAt(final char[] chars, final int offset) {
      return Character.codePointAt(chars, offset);
    }

    @Override
    public int codePointAt(final CharSequence seq, final int offset) {
      return Character.codePointAt(seq, offset);
    }

    @Override
    public int codePointAt(final char[] chars, final int offset, final int limit) {
     return Character.codePointAt(chars, offset, limit);
    }

    @Override
    public boolean fill(final CharacterBuffer buffer, final Reader reader) throws IOException {
      final char[] charBuffer = buffer.buffer;
      buffer.offset = 0;
      charBuffer[0] = buffer.lastTrailingHighSurrogate;
      final int offset = buffer.lastTrailingHighSurrogate == 0 ? 0 : 1;
      buffer.lastTrailingHighSurrogate = 0;
      final int read = reader.read(charBuffer, offset, charBuffer.length
          - offset);
      if (read == -1) {
        buffer.length = offset;
        return offset != 0;
      }
      buffer.length = read + offset;
      // special case if the read returns 0 and the lastTrailingHighSurrogate was set
      if (buffer.length > 1
          && Character.isHighSurrogate(charBuffer[buffer.length - 1])) {
        buffer.lastTrailingHighSurrogate = charBuffer[--buffer.length];
      }
      return true;
    }
  }

  private static final class Java4CharacterUtils extends CharacterUtils {
    Java4CharacterUtils() {
    }

    @Override
    public final int codePointAt(final char[] chars, final int offset) {
      return chars[offset];
    }

    @Override
    public int codePointAt(final CharSequence seq, final int offset) {
      return seq.charAt(offset);
    }

    @Override
    public int codePointAt(final char[] chars, final int offset, final int limit) {
      if(offset >= limit)
        throw new IndexOutOfBoundsException("offset must be less than limit");
      return chars[offset];
    }

    @Override
    public boolean fill(final CharacterBuffer buffer, final Reader reader) throws IOException {
      buffer.offset = 0;
      final int read = reader.read(buffer.buffer);
      if(read == -1)
        return false;
      buffer.length = read;
      return true;
    }

  }
  
  /**
   * A simple IO buffer to use with
   * {@link CharacterUtils#fill(CharacterBuffer, Reader)}.
   */
  public static final class CharacterBuffer {
    
    private final char[] buffer;
    private int offset;
    private int length;
    private char lastTrailingHighSurrogate = 0;
    
    CharacterBuffer(char[] buffer, int offset, int length) {
      this.buffer = buffer;
      this.offset = offset;
      this.length = length;
    }
    
    /**
     * Returns the internal buffer
     * 
     * @return the buffer
     */
    public char[] getBuffer() {
      return buffer;
    }
    
    /**
     * Returns the data offset in the internal buffer.
     * 
     * @return the offset
     */
    public int getOffset() {
      return offset;
    }
    
    /**
     * Return the length of the data in the internal buffer starting at
     * {@link #getOffset()}
     * 
     * @return the length
     */
    public int getLength() {
      return length;
    }
    
    /**
     * Resets the CharacterBuffer. All internals are reset to its default
     * values.
     */
    public void reset() {
      offset = 0;
      length = 0;
      lastTrailingHighSurrogate = 0;
    }
  }

}

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