Http chunk cache is designed for sharing part of http response (on top of JBoss Netty) that is identical for many clients. Response have to be send as http/1.1 chunks. As key is used Google proto buffer, but it is simple to rewrite to something different.

HttpChunkCache.java

/**
 * <pre>
 * Copyright (c) 2013, AVAST Software a.s.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *     * Redistributions of source code must retain the above copyright
 *       notice, this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above copyright
 *       notice, this list of conditions and the following disclaimer in the
 *       documentation and/or other materials provided with the distribution.
 *     * Neither the name of the AVAST Software a.s. nor the
 *       names of its contributors may be used to endorse or promote products
 *       derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER BE LIABLE FOR ANY
 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 * </pre>
 *
 */

import com.google.protobuf.MessageLite;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.util.Map;
import org.jboss.netty.buffer.ChannelBuffer;
import org.jboss.netty.buffer.ChannelBuffers;
import org.jboss.netty.util.CharsetUtil;
import org.jboss.netty.util.internal.ConcurrentWeakKeyHashMap;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Http chunk cache is designed for sharing part of http response that is
 * identical for many clients. Response have to be send as http/1.1 chunks. As
 * key is used Google proto buffer, but it is simple to rewrite to something
 * different.
 *
 * @author karry
 */
public class HttpChunkCache {

  /**
   * Carriage return
   */
  static final byte CR = 13;
  /**
   * Line feed character
   */
  static final byte LF = 10;
  /**
   * carriage return line feed
   */
  static final byte[] CRLF = new byte[]{CR, LF};
  private static final Logger LOGGER = LoggerFactory.getLogger(HttpChunkCache.class);
  private final Map<MessageLite, ByteBuffer> weakMap = new ConcurrentWeakKeyHashMap<MessageLite, ByteBuffer>();

  /**
   * Create new ByteBuffer with shared direct memory filled from bytes of
   * message and packaged into http chunk.
   */
  public ByteBuffer get(MessageLite message) {
    ByteBuffer directByteBuffer = weakMap.get(message);
    if (directByteBuffer != null)
      return directByteBuffer.slice(); // create clone with shared memory area

    byte[] contentBytes = message.toByteArray();
    int contentLength = contentBytes.length;

    // create http chunk (this code is copied from org.jboss.netty.handler.codec.http.HttpMessageEncoder)
    ChannelBuffer chunkBuffer = ChannelBuffers.wrappedBuffer(
            ChannelBuffers.copiedBuffer(
            Integer.toHexString(contentLength),
            CharsetUtil.US_ASCII),
            ChannelBuffers.wrappedBuffer(CRLF),
            ChannelBuffers.wrappedBuffer(contentBytes),
            ChannelBuffers.wrappedBuffer(CRLF));

    // copy buffer to direct buffer - it can be propagate to kernel without copy
    int capacity = chunkBuffer.readableBytes();
    directByteBuffer = ByteBuffer.allocateDirect(capacity).order(ByteOrder.BIG_ENDIAN);
    chunkBuffer.readBytes(directByteBuffer);
    directByteBuffer.flip(); // rewind to begining

    LOGGER.debug("put into cache " + message.hashCode() + " " + (((double) directByteBuffer.capacity()) / 1024d) + " KiB");
    weakMap.put(message, directByteBuffer);
    return directByteBuffer.slice(); // create clone with shared memory area
  }
}