cn.ac.ncic.mastiff.io.coding.RunLengthEncodingByteWriter.java Source code

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Here is the source code for cn.ac.ncic.mastiff.io.coding.RunLengthEncodingByteWriter.java

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/**
 * Copyright 2007 The Apache Software Foundation
 *
 * 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.
 */
package cn.ac.ncic.mastiff.io.coding;

import java.io.IOException;
import java.io.OutputStream;
import java.nio.ByteBuffer;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.io.DataOutputBuffer;

import cn.ac.ncic.mastiff.ValPair;
import cn.ac.ncic.mastiff.io.coding.Compression.Algorithm;
import cn.ac.ncic.mastiff.utils.Bytes;

public class RunLengthEncodingByteWriter extends Encoder {

    static final Log LOG = LogFactory.getLog(FixedLenEncoder.class);
    /** 
     * Which compression algorithm used to compress a page of data 
     * 
     * @see Algorithm
     */
    Algorithm compressAlgo;
    /**
     * Used the compressor provided by hadoop to compress the data
     * 
     * @see org.apache.hadoop.io.compress.Compressor
     */
    org.apache.hadoop.io.compress.Compressor compressor;
    DataOutputBuffer outputBuffer = new DataOutputBuffer();

    /**
     * FixeLenEncoder Constructor
     * 
     * @param pageLen_
     *            the page capacity
     * @param valueLen_
     *            the length of the value
     * @param startPos_
     *            the start position
     * @param algorithm
     *            the compression algorithm
     * 
     * @see Algorithm
     */
    public RunLengthEncodingByteWriter(int pageLen_, int valueLen_, int startPos_, Algorithm algorithm) {
        pageCapacity = pageLen_;
        valueLen = valueLen_;
        startPos = startPos_;
        compressAlgo = algorithm;

        page = new byte[pageCapacity];
        if (LOG.isDebugEnabled()) {
            LOG.debug("FixeLenCompressor : " + pageCapacity + ", " + valueLen + ", " + startPos);
        }
        reset();
    }

    @Override
    public void reset() {
        startPos += numPairs;
        numPairs = 0;
        dataOffset = 3 * Bytes.SIZEOF_INT;
    }

    @Override
    public boolean append(ValPair pair) {
        if (dataOffset + valueLen > pageCapacity) {
            return false;
        }
        System.arraycopy(pair.data, 0, page, dataOffset, pair.length);
        numPairs++;
        dataOffset += valueLen;

        return true;
    }

    @Override
    public boolean appendPage(ValPair pair) {
        page = new byte[pair.length + 12];
        System.arraycopy(pair.data, 0, page, 12, pair.length);
        return true;
    }

    @Override
    public byte[] getPage() throws IOException {
        if (dataOffset == 3 * Bytes.SIZEOF_INT) // no data appended 
            return null;
        /** We do not compressed the page of data */
        if (compressAlgo == null) {
            bb = ByteBuffer.wrap(page, 0, page.length);
            bb.putInt(dataOffset);
            bb.putInt(numPairs);
            bb.putInt(startPos);
            return page;
        } else { // compress a page using the specified <i>Algorithm</i>
            outputBuffer.reset();
            outputBuffer.writeInt(dataOffset);
            outputBuffer.writeInt(numPairs);
            outputBuffer.writeInt(startPos);
            outputBuffer.writeInt(page.length - 12);
            compressor = compressAlgo.getCompressor();
            // create the compression stream
            OutputStream os = this.compressAlgo.createCompressionStream(outputBuffer, compressor, 0);
            os.write(page, 3 * Bytes.SIZEOF_INT, dataOffset - 3 * Bytes.SIZEOF_INT);
            os.flush();
            this.compressAlgo.returnCompressor(compressor);
            this.compressor = null;
            return outputBuffer.getData();
        }
    }

    @Override
    public int getPageLen() {
        if (dataOffset == 3 * Bytes.SIZEOF_INT) // no data appended
            return 0;

        if (compressAlgo == null)
            // return dataOffset;
            return page.length;

        else
            return outputBuffer.getLength();
    }
}