snappy-java/README.md

snappy-java
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=== 
snappy-java is a Java port of the [snappy](https://github.com/google/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`](https://oss.sonatype.org/service/local/repositories/releases/archive/org/xerial/snappy/snappy-java/1.1.8/snappy-java-1.1.8-javadoc.jar/!/org/xerial/snappy/BitShuffle.html)) 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`).
  * 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](https://github.com/google/snappy/blob/master/framing_format.txt) (Since 1.1.0 version)
  * OSGi support
  * [Apache License Version 2.0](http://www.apache.org/licenses/LICENSE-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](https://github.com/ning/jvm-compressor-benchmark/wiki), comparing
 snappy-java and the other compressors
 `LZO-java`/`LZF`/`QuickLZ`/`Gzip`/`Bzip2`. Thanks [Tatu Saloranta @cotowncoder](http://twitter.com/#!/cowtowncoder) for providing the benchmark suite.
  * The benchmark result indicates snappy-java is the fastest compressor/decompressor in Java: https://ning.github.io/jvm-compressor-benchmark/results/canterbury-roundtrip-2011-07-28/index.html
 * The decompression speed is twice as fast as the others: https://ning.github.io/jvm-compressor-benchmark/results/canterbury-uncompress-2011-07-28/index.html


## Download

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 * [Release Notes](Milestone.md)

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:

```java
import org.xerial.snappy.Snappy;
```

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

```java
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](https://github.com/google/snappy/blob/master/framing_format.txt). 

 * See also [Javadoc API](https://oss.sonatype.org/service/local/repositories/releases/archive/org/xerial/snappy/snappy-java/1.1.3-M1/snappy-java-1.1.3-M1-javadoc.jar/!/index.html)

#### 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`:

```java
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](http://static.javadoc.io/org.xerial.snappy/snappy-java/1.1.3-M1/org/xerial/snappy/BitShuffle.html) 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](http://groups.google.com/group/xerial?hl=en)

## 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
    > ~testOnly        # 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](http://xerial.org/blog/2014/03/24/sbt/)

### Building from the source code

See the [build instruction](https://github.com/xerial/snappy-java/blob/master/BUILD.md). 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.

### Creating a new release

GitHub action [https://github.com/xerial/snappy-java/blob/master/.github/workflows/release.yml] will publish a new relase to Maven Central (Sonatype) when a new tag vX.Y.Z is pushed.

## Miscellaneous Notes

### 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) 

----
Snappy-java is developed by [Taro L. Saito](http://www.xerial.org/leo). Twitter  [@taroleo](http://twitter.com/#!/taroleo)