Java压缩算法

一、算法

1.1 DEFLATE

DEFLATE是同时使用了LZ77算法与哈夫曼编码（Huffman Coding）的一个无损数据压缩算法，jdk中对zlib压缩库提供了支持，压缩类Deflater和解压类Inflater，Deflater和Inflater都提供了相应的native方法。

public static byte[] compress(byte input[]) { 
    ByteArrayOutputStream bos = new ByteArrayOutputStream(); Deflater compressor = new Deflater(1); try { 
    compressor.setInput(input); compressor.finish(); final byte[] buf = new byte[2048]; while (!compressor.finished()) { 
    int count = compressor.deflate(buf); bos.write(buf, 0, count); } } finally { 
    compressor.end(); } return bos.toByteArray(); } public static byte[] uncompress(byte[] input) throws DataFormatException { 
    ByteArrayOutputStream bos = new ByteArrayOutputStream(); Inflater decompressor = new Inflater(); try { 
    decompressor.setInput(input); final byte[] buf = new byte[2048]; while (!decompressor.finished()) { 
    int count = decompressor.inflate(buf); bos.write(buf, 0, count); } } finally { 
    decompressor.end(); } return bos.toByteArray(); } 

1.2 gzip

gzip的实现算法还是deflate，只是在deflate格式上增加了文件头和文件尾，同样jdk也对gzip提供了支持，分别是GZIPOutputStream和GZIPInputStream类，同样可以发现GZIPOutputStream是继承于DeflaterOutputStream的，GZIPInputStream继承于InflaterInputStream，并且可以在源码中发现writeHeader和writeTrailer方法。

public static byte[] compress(byte srcBytes[]) { 
    ByteArrayOutputStream out = new ByteArrayOutputStream(); GZIPOutputStream gzip; try { 
    gzip = new GZIPOutputStream(out); gzip.write(srcBytes); gzip.close(); } catch (IOException e) { 
    e.printStackTrace(); } return out.toByteArray(); } public static byte[] uncompress(byte[] bytes) { 
    ByteArrayOutputStream out = new ByteArrayOutputStream(); ByteArrayInputStream in = new ByteArrayInputStream(bytes); try { 
    GZIPInputStream ungzip = new GZIPInputStream(in); byte[] buffer = new byte[2048]; int n; while ((n = ungzip.read(buffer)) >= 0) { 
    out.write(buffer, 0, n); } } catch (IOException e) { 
    e.printStackTrace(); } return out.toByteArray(); } 

1.3 bzip2

bzip2是Julian Seward开发并按照自由软件／开源软件协议发布的数据压缩算法及程序。Seward在1996年7月第一次公开发布了bzip2 0.15版，在随后几年中这个压缩工具稳定性得到改善并且日渐流行，Seward在2000年晚些时候发布了1.0版。bzip2比传统的gzip的压缩效率更高，但是它的压缩速度较慢。jdk中没有对bzip2实现，但是在commons-compress中进行了实现。

<dependency> <groupId>org.apache.commons</groupId> <artifactId>commons-compress</artifactId> <version>1.12</version> </dependency> 

代码实现如下：

public static byte[] compress(byte srcBytes[]) throws IOException { 
    ByteArrayOutputStream out = new ByteArrayOutputStream(); BZip2CompressorOutputStream bcos = new BZip2CompressorOutputStream(out); bcos.write(srcBytes); bcos.close(); return out.toByteArray(); } public static byte[] uncompress(byte[] bytes) { 
    ByteArrayOutputStream out = new ByteArrayOutputStream(); ByteArrayInputStream in = new ByteArrayInputStream(bytes); try { 
    BZip2CompressorInputStream ungzip = new BZip2CompressorInputStream( in); byte[] buffer = new byte[2048]; int n; while ((n = ungzip.read(buffer)) >= 0) { 
    out.write(buffer, 0, n); } } catch (IOException e) { 
    e.printStackTrace(); } return out.toByteArray(); } 

1.4 lzo

LZO是致力于解压速度的一种数据压缩算法，LZO是Lempel-Ziv-Oberhumer的缩写。这个算法是无损算法，需要引入第三方库。

<dependency> <groupId>org.anarres.lzo</groupId> <artifactId>lzo-core</artifactId> <version>1.0.5</version> </dependency> 

实现代码：

public static byte[] compress(byte srcBytes[]) throws IOException { 
    LzoCompressor compressor = LzoLibrary.getInstance().newCompressor( LzoAlgorithm.LZO1X, null); ByteArrayOutputStream os = new ByteArrayOutputStream(); LzoOutputStream cs = new LzoOutputStream(os, compressor); cs.write(srcBytes); cs.close(); return os.toByteArray(); } public static byte[] uncompress(byte[] bytes) throws IOException { 
    LzoDecompressor decompressor = LzoLibrary.getInstance() .newDecompressor(LzoAlgorithm.LZO1X, null); ByteArrayOutputStream baos = new ByteArrayOutputStream(); ByteArrayInputStream is = new ByteArrayInputStream(bytes); LzoInputStream us = new LzoInputStream(is, decompressor); int count; byte[] buffer = new byte[2048]; while ((count = us.read(buffer)) != -1) { 
    baos.write(buffer, 0, count); } return baos.toByteArray(); } 

1.5 lz4

LZ4是一种无损数据压缩算法，着重于压缩和解压缩速度，需要依赖三方库。

<dependency> <groupId>net.jpountz.lz4</groupId> <artifactId>lz4</artifactId> <version>1.2.0</version> </dependency> 

实现代码：

public static byte[] compress(byte srcBytes[]) throws IOException { 
    LZ4Factory factory = LZ4Factory.fastestInstance(); ByteArrayOutputStream byteOutput = new ByteArrayOutputStream(); LZ4Compressor compressor = factory.fastCompressor(); LZ4BlockOutputStream compressedOutput = new LZ4BlockOutputStream( byteOutput, 2048, compressor); compressedOutput.write(srcBytes); compressedOutput.close(); return byteOutput.toByteArray(); } public static byte[] uncompress(byte[] bytes) throws IOException { 
    LZ4Factory factory = LZ4Factory.fastestInstance(); ByteArrayOutputStream baos = new ByteArrayOutputStream(); LZ4FastDecompressor decompresser = factory.fastDecompressor(); LZ4BlockInputStream lzis = new LZ4BlockInputStream( new ByteArrayInputStream(bytes), decompresser); int count; byte[] buffer = new byte[2048]; while ((count = lzis.read(buffer)) != -1) { 
    baos.write(buffer, 0, count); } lzis.close(); return baos.toByteArray(); } 

1.6 Snappy

Snappy（以前称Zippy）是Google基于LZ77的思路用C++语言编写的快速数据压缩与解压程序库，并在2011年开源。它的目标并非最大压缩率或与其他压缩程序库的兼容性，而是非常高的速度和合理的压缩率。

<dependency> <groupId>org.xerial.snappy</groupId> <artifactId>snappy-java</artifactId> <version>1.1.2.6</version> </dependency> 

实现代码：

public static byte[] compress(byte srcBytes[]) throws IOException { 
    return Snappy.compress(srcBytes); } public static byte[] uncompress(byte[] bytes) throws IOException { 
    return Snappy.uncompress(bytes); } 

二、压力测试

以下对35kb玩家数据进行压缩和解压测试，相对来说35kb数据还是很小量的数据，所有以下测试结果只是针对指定的数据量区间进行测试的结果，并不能说明哪种压缩算法好与不好。

测试环境：

• jdk：1.7.0_79
• cpu：i5-4570@3.20GHz 4 Core
• memory：4G

对35kb数据进行2000次压缩和解压缩测试，测试代码如下：

public static void main(String[] args) throws Exception { 
    FileInputStream fis = new FileInputStream(new File("player.dat")); FileChannel channel = fis.getChannel(); ByteBuffer bb = ByteBuffer.allocate((int) channel.size()); channel.read(bb); byte[] beforeBytes = bb.array(); int times = 2000; System.out.println("压缩前大小：" + beforeBytes.length + " bytes"); long startTime1 = System.currentTimeMillis(); byte[] afterBytes = null; for (int i = 0; i < times; i++) { 
    afterBytes = GZIPUtil.compress(beforeBytes); } long endTime1 = System.currentTimeMillis(); System.out.println("压缩后大小：" + afterBytes.length + " bytes"); System.out.println("压缩次数：" + times + "，时间：" + (endTime1 - startTime1) + "ms"); byte[] resultBytes = null; long startTime2 = System.currentTimeMillis(); for (int i = 0; i < times; i++) { 
    resultBytes = GZIPUtil.uncompress(afterBytes); } System.out.println("解压缩后大小：" + resultBytes.length + " bytes"); long endTime2 = System.currentTimeMillis(); System.out.println("解压缩次数：" + times + "，时间：" + (endTime2 - startTime2) + "ms"); } 

三、总结

从结果来看，deflate、gzip和bzip2更关注压缩率，压缩和解压缩时间会更长；lzo，lz4以及snappy这3中压缩算法，均已压缩速度为优先，压缩率会稍逊一筹；lzo，lz4以及snappy在cpu高峰更低一点。