IntEncoder.java

package org.apache.lucene.util.encoding;

import java.io.IOException;
import java.io.OutputStream;

/*
 * 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.
 */

/**
 * Encodes integers to a set {@link OutputStream}. Extending classes need to
 * override {@link #encode(int)} to encode the value using their encoding
 * algorithm. The default implementation of {@link #close()} closes the set
 * {@link OutputStream}.
 * <p>
 * The default {@link #IntEncoder() constructor} is provided for convenience
 * only. One must call {@link #reInit(OutputStream)} before calling
 * {@link #encode(int)} or {@link #close()}.
 * <p>
 * For convenience, each encoder implements {@link #createMatchingDecoder()} for
 * easy access to the matching decoder.
 * <p>
 * <b>NOTE:</b> some implementations may buffer the encoded values in memory
 * (such as {@link IntEncoderFilter} implementations) and encoding will happen
 * only upon calling {@link #close()}. Therefore it is important to always call
 * {@link #close()} on the encoder at hand.
 * <p>
 * <b>NOTE:</b> encoders are usually not thread safe, unless specifically
 * documented otherwise by an implementation.
 * 
 * @lucene.experimental
 */
public abstract class IntEncoder {

  protected OutputStream out = null;

  /**
   * Default constructor, provided here for robustness: if in the future a
   * constructor with parameters will be added, this might break custom
   * implementations of this class which call this implicit constructor. So we
   * make it explicit to avoid any such issue in the future.
   */
  public IntEncoder() {
  }

  /**
   * Instructs the encoder to finish the encoding process. This method closes
   * the output stream which was specified by {@link #reInit(OutputStream)
   * reInit}. An implementation may do here additional cleanup required to
   * complete the encoding, such as flushing internal buffers, etc.<br>
   * Once this method was called, no further calls to {@link #encode(int)
   * encode} should be made before first calling {@link #reInit(OutputStream)
   * reInit}.
   * <p>
   * <b>NOTE:</b> overriding classes should make sure they either call
   * <code>super.close()</code> or close the output stream themselves.
   */
  public void close() throws IOException {
    if (out != null) {
      out.close();
    }
  }

  /**
   * Encodes an integer to the output stream given in
   * {@link #reInit(OutputStream) reInit}
   */
  public abstract void encode(int value) throws IOException;

  /**
   * Returns an {@link IntDecoder} which matches this encoder. Every encoder
   * must return an {@link IntDecoder} and <code>null</code> is not a valid
   * value. If an encoder is just a filter, it should at least return its
   * wrapped encoder's matching decoder.
   * <p>
   * <b>NOTE:</b> this method should create a new instance of the matching
   * decoder and leave the instance sharing to the caller. Returning the same
   * instance over and over is risky because encoders and decoders are not
   * thread safe.
   */
  public abstract IntDecoder createMatchingDecoder();
  
  /**
   * Reinitializes the encoder with the give {@link OutputStream}. For
   * re-usability it can be changed without the need to reconstruct a new
   * object.
   * <p>
   * <b>NOTE:</b> after calling {@link #close()}, one <u><i>must</i></u> call
   * this method even if the output stream itself hasn't changed. An example
   * case is that the output stream wraps a byte[], and the output stream itself
   * is reset, but its instance hasn't changed. Some implementations of
   * {@link IntEncoder} may write some metadata about themselves to the output
   * stream, and therefore it is imperative that one calls this method before
   * encoding any data.
   */
  public void reInit(OutputStream out) {
    this.out = out;
  }

}