Java tutorial
/* * 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 org.apache.hadoop.io.compress.snappy; import java.io.IOException; import java.nio.Buffer; import java.nio.ByteBuffer; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import org.apache.hadoop.io.compress.Decompressor; /** * A {@link Decompressor} based on the snappy compression algorithm. * http://code.google.com/p/snappy/ */ public class SnappyDecompressor implements Decompressor { private static final Log LOG = LogFactory.getLog(SnappyCompressor.class.getName()); private static final int DEFAULT_DIRECT_BUFFER_SIZE = 64 * 1024; // HACK - Use this as a global lock in the JNI layer @SuppressWarnings({ "unchecked", "unused" }) private static Class clazz = SnappyDecompressor.class; private int directBufferSize; private Buffer compressedDirectBuf = null; private int compressedDirectBufLen; private Buffer uncompressedDirectBuf = null; private byte[] userBuf = null; private int userBufOff = 0, userBufLen = 0; private boolean finished; static { if (LoadSnappy.isLoaded()) { // Initialize the native library try { initIDs(); } catch (Throwable t) { // Ignore failure to load/initialize snappy LOG.warn(t.toString()); } } else { LOG.error("Cannot load " + SnappyDecompressor.class.getName() + " without snappy library!"); } } /** * Creates a new compressor. * * @param directBufferSize size of the direct buffer to be used. */ public SnappyDecompressor(int directBufferSize) { this.directBufferSize = directBufferSize; compressedDirectBuf = ByteBuffer.allocateDirect(directBufferSize); uncompressedDirectBuf = ByteBuffer.allocateDirect(directBufferSize); uncompressedDirectBuf.position(directBufferSize); } /** * Creates a new decompressor with the default buffer size. */ public SnappyDecompressor() { this(DEFAULT_DIRECT_BUFFER_SIZE); } /** * Sets input data for decompression. * This should be called if and only if {@link #needsInput()} returns * <code>true</code> indicating that more input data is required. * (Both native and non-native versions of various Decompressors require * that the data passed in via <code>b[]</code> remain unmodified until * the caller is explicitly notified--via {@link #needsInput()}--that the * buffer may be safely modified. With this requirement, an extra * buffer-copy can be avoided.) * * @param b Input data * @param off Start offset * @param len Length */ @Override public synchronized void setInput(byte[] b, int off, int len) { if (b == null) { throw new NullPointerException(); } if (off < 0 || len < 0 || off > b.length - len) { throw new ArrayIndexOutOfBoundsException(); } this.userBuf = b; this.userBufOff = off; this.userBufLen = len; setInputFromSavedData(); // Reinitialize snappy's output direct-buffer uncompressedDirectBuf.limit(directBufferSize); uncompressedDirectBuf.position(directBufferSize); } /** * If a write would exceed the capacity of the direct buffers, it is set * aside to be loaded by this function while the compressed data are * consumed. */ synchronized void setInputFromSavedData() { compressedDirectBufLen = Math.min(userBufLen, directBufferSize); // Reinitialize snappy's input direct buffer compressedDirectBuf.rewind(); ((ByteBuffer) compressedDirectBuf).put(userBuf, userBufOff, compressedDirectBufLen); // Note how much data is being fed to snappy userBufOff += compressedDirectBufLen; userBufLen -= compressedDirectBufLen; } /** * Does nothing. */ @Override public synchronized void setDictionary(byte[] b, int off, int len) { // do nothing } /** * Returns true if the input data buffer is empty and * {@link #setInput(byte[], int, int)} should be called to * provide more input. * * @return <code>true</code> if the input data buffer is empty and * {@link #setInput(byte[], int, int)} should be called in * order to provide more input. */ @Override public synchronized boolean needsInput() { // Consume remaining compressed data? if (uncompressedDirectBuf.remaining() > 0) { return false; } // Check if snappy has consumed all input if (compressedDirectBufLen <= 0) { // Check if we have consumed all user-input if (userBufLen <= 0) { return true; } else { setInputFromSavedData(); } } return false; } /** * Returns <code>false</code>. * * @return <code>false</code>. */ @Override public synchronized boolean needsDictionary() { return false; } /** * Returns true if the end of the decompressed * data output stream has been reached. * * @return <code>true</code> if the end of the decompressed * data output stream has been reached. */ @Override public synchronized boolean finished() { return (finished && uncompressedDirectBuf.remaining() == 0); } /** * Fills specified buffer with uncompressed data. Returns actual number * of bytes of uncompressed data. A return value of 0 indicates that * {@link #needsInput()} should be called in order to determine if more * input data is required. * * @param b Buffer for the compressed data * @param off Start offset of the data * @param len Size of the buffer * @return The actual number of bytes of compressed data. * @throws IOException */ @Override public synchronized int decompress(byte[] b, int off, int len) throws IOException { if (b == null) { throw new NullPointerException(); } if (off < 0 || len < 0 || off > b.length - len) { throw new ArrayIndexOutOfBoundsException(); } int n = 0; // Check if there is uncompressed data n = uncompressedDirectBuf.remaining(); if (n > 0) { n = Math.min(n, len); ((ByteBuffer) uncompressedDirectBuf).get(b, off, n); return n; } if (compressedDirectBufLen > 0) { // Re-initialize the snappy's output direct buffer uncompressedDirectBuf.rewind(); uncompressedDirectBuf.limit(directBufferSize); // Decompress data n = decompressBytesDirect(); uncompressedDirectBuf.limit(n); if (userBufLen <= 0) { finished = true; } // Get atmost 'len' bytes n = Math.min(n, len); ((ByteBuffer) uncompressedDirectBuf).get(b, off, n); } return n; } /** * Returns <code>0</code>. * * @return <code>0</code>. */ @Override public synchronized int getRemaining() { // Never use this function in BlockDecompressorStream. return 0; } public synchronized void reset() { finished = false; compressedDirectBufLen = 0; uncompressedDirectBuf.limit(directBufferSize); uncompressedDirectBuf.position(directBufferSize); userBufOff = userBufLen = 0; } /** * Resets decompressor and input and output buffers so that a new set of * input data can be processed. */ @Override public synchronized void end() { // do nothing } private native static void initIDs(); private native int decompressBytesDirect(); }