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Snappy是Google开源的压缩/解压缩库。和其他压缩库相比，snappy的压缩率并不是最高的，兼容性也并非最好的。相反，它的诞生旨在以极高的压缩/解压缩速率提供合理的压缩率。Snappy官指出：在64位单核core-i7处理器下，snappy的压缩率能够达到250MB/S，而解压缩速度则能达到500MB/S。目前很多软件使用（或支持）snappy作为压缩库，如MongoDB,Cassandra,Hadoop,Lucene…本文简单介绍snappy Java Api的使用。

Snappy提供了很多高级API以方便对byte[],Sting,double[]等进行压缩和解压缩，示例代码如下：

import org.xerial.snappy.Snappy;String input = "Hello snappy-java! Snappy-java is a JNI-based wrapper of Snappy, a fast compresser/decompresser.";{     byte[] compressed = Snappy.compress(input.getBytes("UTF-8"));    byte[] uncompressed = Snappy.uncompress(compressed);    String result = new String(uncompressed, "UTF-8");    System.out.println(result);}{    byte[] compressed = Snappy.compress(input);    System.out.println(Snappy.uncompressString(compressed));}{    double [] arr = new double[]{
  123.456,234.567,345.678};    byte[] compressed = Snappy.compress(arr);    double [] unarr = Snappy.uncompressDoubleArray(compressed);    System.out.println(Arrays.toString(unarr));}

同时Snappy仍然保留着低级API，用于最小化内存的拷贝，例如

/**inputAddr:待压缩数据的内存地址*inputSize:待压缩数据的byte size*destAddr:压缩结果的保存地址*return：返回压缩后数据的大小*/public static long rawCompress(long inputAddr,long inputSize, long destAddr)throws java.io.IOException;/**inputAddr:待解压缩数据的内存地址*inputSize:待解压缩数据的byte size*destAddr:解压缩结果的保存地址*return：返回解压缩后数据的大小*/public static long rawUncompress(long inputAddr,long inputSize,long destAddr)throws java.io.IOException;

基于输入/输出流的Snappy解压缩

SnappyOutputStream和SnappyInputStream分别用于流数据的压缩/解压缩。此外，从snappy v1.1.0开始提供了Framing-format(帧格式)输入输出流的压缩/解压缩的方法：SnappyFramedOutputStream和SnappyFramedInputStream。需要注意的是以SnappyOutputStream压缩的数据不能以SnappyFramedInputStream方法解开，反之亦然。下面以SnappyOutputStream和SnappyInputStream为例介绍。 SnappyOutputStream继承自java.io OutputStream,重写了常用的的write,close,flush:

File file = new File("..."); //待压缩文件File out = new File("./", file.getName() + ".snappy"); //压缩结果文件byte[] buffer = new byte[1024 * 1024 * 8];FileInputStream  fi = null;FileOutputStream fo = null;SnappyOutputStream sout = null;try{    fi = new FileInputStream(file);     fo = new FileOutputStream(out);    sout = new SnappyOutputStream(fo);    while(true)    {        int count = fi.read(buffer, 0, buffer.length);        if(count == -1) { break; }        sout.write(buffer, 0, count);    }    sout.flush();}catch(Throwable ex){    ex.printStackTrace();}finally {    if(sout != null) {
  try { sout.close();} catch (Exception e) {}}    if(fi != null) { try { fi.close(); } catch(Exception x) {} }    if(fo != null) { try { fo.close(); } catch(Exception x) {} }}

SnappyInputStream 继承自java.io InputStream,重写了常用的read,close方法等

File file = new File("xxx"); //待解压文件File out = new File("xxx");  //解压后文件byte[] buffer = new byte[1024 * 1024 * 8];FileInputStream  fi = null;FileOutputStream fo = null;SnappyInputStream sin = null;try{    fo = new FileOutputStream(out);    fi = new FileInputStream(file.getPath());    sin = new SnappyInputStream(fi);            while(true)    {        int count = sin.read(buffer, 0, buffer.length);        if(count == -1) { break; }        fo.write(buffer, 0, count);    }    fo.flush();}catch(Throwable ex){    ex.printStackTrace();}finally {    if(sin != null) { try { sin.close(); } catch(Exception x) {} }    if(fi != null) { try { fi.close(); } catch(Exception x) {} }    if(fo != null) { try { fo.close(); } catch(Exception x) {} }}

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