DefaultCodecProvider.java

/*
Copyright (c) 2010 James Ahlborn

Licensed 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.
*/

package com.healthmarketscience.jackcess.impl;

import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.charset.Charset;

/**
 * Default implementation of CodecProvider which does not have any actual
 * encoding/decoding support.  See {@link CodecProvider} for details on a more
 * useful implementation.
 *
 * @author James Ahlborn
 */
public class DefaultCodecProvider implements CodecProvider
{
  /** common instance of DefaultCodecProvider */
  public static final CodecProvider INSTANCE = 
    new DefaultCodecProvider();

  /** common instance of {@link DummyHandler} */
  public static final CodecHandler DUMMY_HANDLER = 
    new DummyHandler();

  /** common instance of {@link UnsupportedHandler} */
  public static final CodecHandler UNSUPPORTED_HANDLER = 
    new UnsupportedHandler();


  /**
   * {@inheritDoc}
   * <p>
   * This implementation returns DUMMY_HANDLER for databases with no encoding
   * and UNSUPPORTED_HANDLER for databases with any encoding.
   */
  public CodecHandler createHandler(PageChannel channel, Charset charset)
    throws IOException
  {
    JetFormat format = channel.getFormat();
    switch(format.CODEC_TYPE) {
    case NONE:
      // no encoding, all good
      return DUMMY_HANDLER;

    case JET:
    case OFFICE:
      // check for an encode key.  if 0, not encoded
      ByteBuffer bb = channel.createPageBuffer();
      channel.readPage(bb, 0);
      int codecKey = bb.getInt(format.OFFSET_ENCODING_KEY);
      return((codecKey == 0) ? DUMMY_HANDLER : UNSUPPORTED_HANDLER);

    case MSISAM:
      // always encoded, we don't handle it
      return UNSUPPORTED_HANDLER;

    default:
      throw new RuntimeException("Unknown codec type " + format.CODEC_TYPE);
    }
  }

  /**
   * CodecHandler implementation which does nothing, useful for databases with
   * no extra encoding.
   */
  public static class DummyHandler implements CodecHandler
  {
    public boolean canEncodePartialPage() {
      return true;
    }

    public boolean canDecodeInline() {
      return true;
    }

    public void decodePage(ByteBuffer inPage, ByteBuffer outPage,
                           int pageNumber) 
      throws IOException 
    {
      // does nothing
    }

    public ByteBuffer encodePage(ByteBuffer page, int pageNumber, 
                                 int pageOffset) 
      throws IOException
    {
      // does nothing
      return page;
    }
  }

  /**
   * CodecHandler implementation which always throws
   * UnsupportedCodecException, useful for databases with unsupported
   * encodings.
   */
  public static class UnsupportedHandler implements CodecHandler
  {
    public boolean canEncodePartialPage() {
      return true;
    }

    public boolean canDecodeInline() {
      return true;
    }

    public void decodePage(ByteBuffer inPage, ByteBuffer outPage, 
                           int pageNumber) 
      throws IOException 
    {
      throw new UnsupportedCodecException("Decoding not supported.  Please choose a CodecProvider which supports reading the current database encoding.");
    }

    public ByteBuffer encodePage(ByteBuffer page, int pageNumber, 
                                 int pageOffset) 
      throws IOException
    {
      throw new UnsupportedCodecException("Encoding not supported.  Please choose a CodecProvider which supports writing the current database encoding.");
    }
  }

}