snappy-java

snappy-java is a Java port of the snappy, a fast C++ compresser/decompresser developed by Google.

Features

• Fast compression/decompression around 200~400MB/sec.
• Less memory usage. SnappyOutputStream uses only 32KB+ in default.
• JNI-based implementation to achieve comparable performance to the native C++ version.
  • Although snappy-java uses JNI, it can be used safely with multiple class loaders (e.g. Tomcat, etc.).
• Compression/decompression of Java primitive arrays (float[], double[], int[], short[], long[], etc.)
  • To improve the compression ratios of these arrays, you can use a fast data-rearrangement implementation (BitShuffle) before compression
• Portable across various operating systems; Snappy-java contains native libraries built for Window/Mac/Linux, etc. snappy-java loads one of these libraries according to your machine environment (It looks system properties, os.name and os.arch).
  • If no native library for your platform is found, snappy-java will fallback to pure-java implementation.
• Simple usage. Add the snappy-java-(version).jar file to your classpath. Then call compression/decompression methods in org.xerial.snappy.Snappy.
• Framing-format support (Since 1.1.0 version)
• OSGi support
• Apache License Version 2.0. Free for both commercial and non-commercial use.

Performance

• Snappy's main target is very high-speed compression/decompression with reasonable compression size. So the compression ratio of snappy-java is modest and about the same as LZF (ranging 20%-100% according to the dataset).

• Here are some benchmark results, comparing snappy-java and the other compressors LZO-java/LZF/QuickLZ/Gzip/Bzip2. Thanks Tatu Saloranta @cotowncoder for providing the benchmark suite.

• The benchmark result indicates snappy-java is the fastest compreesor/decompressor in Java: http://ning.github.com/jvm-compressor-benchmark/results/canterbury-roundtrip-2011-07-28/index.html

• The decompression speed is twice as fast as the others: http://ning.github.com/jvm-compressor-benchmark/results/canterbury-uncompress-2011-07-28/index.html

Download

• Release Notes

The current stable version is available from here:

• Release version: https://repo1.maven.org/maven2/org/xerial/snappy/snappy-java/
• Snapshot version (the latest beta version): https://oss.sonatype.org/content/repositories/snapshots/org/xerial/snappy/snappy-java/

Using with Maven

Snappy-java is available from Maven's central repository. Add the following dependency to your pom.xml:

<dependency>
  <groupId>org.xerial.snappy</groupId>
  <artifactId>snappy-java</artifactId>
  <version>(version)</version>
  <type>jar</type>
  <scope>compile</scope>
</dependency>

Using with sbt

libraryDependencies += "org.xerial.snappy" % "snappy-java" % "(version)"

Usage

First, import org.xerial.snapy.Snappy in your Java code:

import org.xerial.snappy.Snappy;

Then use Snappy.compress(byte[]) and Snappy.uncompress(byte[]):

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);

In addition, high-level methods (Snappy.compress(String), Snappy.compress(float[] ..) etc. ) and low-level ones (e.g. Snappy.rawCompress(.. ), Snappy.rawUncompress(..), etc.), which minimize memory copies, can be used.

Stream-based API

Stream-based compressor/decompressor SnappyOutputStream/SnappyInputStream are also available for reading/writing large data sets. SnappyFramedOutputStream/SnappyFramedInputStream can be used for the framing format.

• See also Javadoc API

Compatibility Notes

The original Snappy format definition did not define a file format. It later added a "framing" format to define a file format, but by this point major software was already using an industry standard instead -- represented in this library by the SnappyOutputStream and SnappyInputStream methods.

For interoperability with other libraries, check that compatible formats are used. Note that not all libraries support all variants.

• SnappyOutputStream and SnappyInputStream use [magic header:16 bytes]([block size:int32][compressed data:byte array])* format. You can read the result of Snappy.compress with SnappyInputStream, but you cannot read the compressed data generated by SnappyOutputStream with Snappy.uncompress.
• SnappyHadoopCompatibleOutputStream does not emit a file header but write out the current block size as a preemble to each block

Data format compatibility matrix:

Write\Read	Snappy.uncompress	SnappyInputStream	SnappyFramedInputStream	org.apache.hadoop.io.compress.SnappyCodec
Snappy.compress	ok	ok	x	x
SnappyOutputStream	x	ok	x	x
SnappyFramedOutputStream	x	x	ok	x
SnappyHadoopCompatibleOutputStream	x	x	x	ok

BitShuffle API (Since 1.1.3-M2)

BitShuffle is an algorithm that reorders data bits (shuffle) for efficient compression (e.g., a sequence of integers, float values, etc.). To use BitShuffle routines, import org.xerial.snapy.BitShuffle:

import org.xerial.snappy.BitShuffle;

int[] data = new int[] {1, 3, 34, 43, 34};
byte[] shuffledByteArray = BitShuffle.shuffle(data);
byte[] compressed = Snappy.compress(shuffledByteArray);
byte[] uncompressed = Snappy.uncompress(compressed);
int[] result = BitShuffle.unshuffleIntArray(uncompress);

System.out.println(result);

Shuffling and unshuffling of primitive arrays (e.g., short[], long[], float[], double[], etc.) are supported. See Javadoc for the details.

Setting classpath

If you have snappy-java-(VERSION).jar in the current directory, use -classpath option as follows:

$ javac -classpath ".;snappy-java-(VERSION).jar" Sample.java  # in Windows
or
$ javac -classpath ".:snappy-java-(VERSION).jar" Sample.java  # in Mac or Linux

Public discussion group

Post bug reports or feature request to the Issue Tracker: https://github.com/xerial/snappy-java/issues

Public discussion forum is here: Xerial Public Discussion Group

For developers

snappy-java uses sbt (simple build tool for Scala) as a build tool. Here is a simple usage

$ ./sbt            # enter sbt console
> ~test            # run tests upon source code change
> ~test-only *     # run tests that matches a given name pattern  
> publishM2        # publish jar to $HOME/.m2/repository
> package          # create jar file
> findbugs         # Produce findbugs report in target/findbugs
> jacoco:cover     # Report the code coverage of tests to target/jacoco folder    

If you need to see detailed debug messages, launch sbt with -Dloglevel=debug option:

$ ./sbt -Dloglevel=debug

For the details of sbt usage, see my blog post: Building Java Projects with sbt

Building from the source code

See the build instruction. Building from the source code is an option when your OS platform and CPU architecture is not supported. To build snappy-java, you need Git, JDK (1.6 or higher), g++ compiler (mingw in Windows) etc.

$ git clone https://github.com/xerial/snappy-java.git
$ cd snappy-java
$ make

When building on Solaris, use gmake:

$ gmake

A file target/snappy-java-$(version).jar is the product additionally containing the native library built for your platform.

Miscellaneous Notes

Using pure-java Snappy implementation

snappy-java can optionally use a pure-java implementation of Snappy based on aircompressor. This implementation is selected when no native Snappy library for your platform is found. You can also force using this pure-java implementation by setting a JVM property org.xerial.snappy.purejava=true before loading any class of Snappy (e.g., using -Dorg.xerial.snappy.purejava=true option when launching JVM).

Using snappy-java with Tomcat 6 (or higher) Web Server

Simply put the snappy-java's jar to WEB-INF/lib folder of your web application. Usual JNI-library specific problem no longer exists since snappy-java version 1.0.3 or higher can be loaded by multiple class loaders.

Configure snappy-java using property file

Prepare org-xerial-snappy.properties file (under the root path of your library) in Java's property file format. Here is a list of the available properties:

• org.xerial.snappy.lib.path (directory containing a snappyjava's native library)
• org.xerial.snappy.lib.name (library file name)
• org.xerial.snappy.tempdir (temporary directory to extract a native library bundled in snappy-java)
• org.xerial.snappy.use.systemlib (if this value is true, use system installed libsnappyjava.so looking the path specified by java.library.path)

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Snappy-java is developed by Taro L. Saito. Twitter @taroleo