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https://github.com/lz4/lz4-java

LZ4 compression for Java
https://github.com/lz4/lz4-java

compressor decompression java jni-bindings lz4-compression lz4-compressors lz4-java

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LZ4 compression for Java

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README 

        
# LZ4 Java



LZ4 compression for Java, based on Yann Collet's work available at

http://code.google.com/p/lz4/.



This library provides access to two compression methods that both generate a

valid LZ4 stream:

 - fast scan (LZ4):

   - low memory footprint (~ 16 KB),

   - very fast (fast scan with skipping heuristics in case the input looks

     incompressible),

   - reasonable compression ratio (depending on the redundancy of the input).

 - high compression (LZ4 HC):

   - medium memory footprint (~ 256 KB),

   - rather slow (~ 10 times slower than LZ4),

   - good compression ratio (depending on the size and the redundancy of the

     input).

 - interoperable (LZ4 Frame):

   - overlay on top of lz4, that makes it system and library independent

   - this is the version to employ in order to share lz4 compressed data

     with other systems using different lz4 frameworks.



The streams produced by LZ4 and LZ4 HC use the same compression format,

are very fast to decompress and can be decompressed by the same lz4-java decompressor instance.



The streams produced by LZ4 Frame can be read by other independent implementations of LZ4 Frame in any other language, including the `lz4` CLI tool.



## Implementations



For LZ4 compressors, LZ4 HC compressors and decompressors, 3 implementations are

available:

 - JNI bindings to the original C implementation by Yann Collet,

 - a pure Java port of the compression and decompression algorithms,

 - a Java port that uses the sun.misc.Unsafe API in order to achieve compression

   and decompression speeds close to the C implementation.



Have a look at LZ4Factory for more information.



## Compatibility notes



 - Compressors and decompressors are interchangeable: it is perfectly correct

   to compress with the JNI bindings and to decompress with a Java port, or the

   other way around.



 - Compressors might not generate the same compressed streams on all platforms,

   especially if CPU endianness differs, but the compressed streams can be

   safely decompressed by any decompressor implementation on any platform.



## Examples



```java

LZ4Factory factory = LZ4Factory.fastestInstance();



byte[] data = "12345345234572".getBytes("UTF-8");

final int decompressedLength = data.length;



// compress data

LZ4Compressor compressor = factory.fastCompressor();

int maxCompressedLength = compressor.maxCompressedLength(decompressedLength);

byte[] compressed = new byte[maxCompressedLength];

int compressedLength = compressor.compress(data, 0, decompressedLength, compressed, 0, maxCompressedLength);



// decompress data

// - method 1: when the decompressed length is known

LZ4FastDecompressor decompressor = factory.fastDecompressor();

byte[] restored = new byte[decompressedLength];

int compressedLength2 = decompressor.decompress(compressed, 0, restored, 0, decompressedLength);

// compressedLength == compressedLength2



// - method 2: when the compressed length is known (a little slower)

// the destination buffer needs to be over-sized

LZ4SafeDecompressor decompressor2 = factory.safeDecompressor();

int decompressedLength2 = decompressor2.decompress(compressed, 0, compressedLength, restored, 0);

// decompressedLength == decompressedLength2

```



```java

byte[] data = "12345345234572".getBytes("UTF-8");

final int decompressedLength = data.length;



LZ4FrameOutputStream outStream = new LZ4FrameOutputStream(new FileOutputStream(new File("test.lz4")));

outStream.write(data);

outStream.close();



byte[] restored = new byte[decompressedLength];

LZ4FrameInputStream inStream = new LZ4FrameInputStream(new FileInputStream(new File("test.lz4")));

inStream.read(restored);

inStream.close();

```



# xxhash Java



xxhash hashing for Java, based on Yann Collet's work available at https://github.com/Cyan4973/xxHash (old version

http://code.google.com/p/xxhash/). xxhash is a non-cryptographic, extremly fast

and high-quality ([SMHasher](http://code.google.com/p/smhasher/wiki/SMHasher)

score of 10) hash function.



## Implementations



Similarly to LZ4, 3 implementations are available: JNI bindings, pure Java port

and pure Java port that uses sun.misc.Unsafe.



Have a look at XXHashFactory for more information.



## Compatibility notes



 - All implementation return the same hash for the same input bytes:

   - on any JVM,

   - on any platform (even if the endianness or integer size differs).



## Example



```java

XXHashFactory factory = XXHashFactory.fastestInstance();



byte[] data = "12345345234572".getBytes("UTF-8");

ByteArrayInputStream in = new ByteArrayInputStream(data);



int seed = 0x9747b28c; // used to initialize the hash value, use whatever

                       // value you want, but always the same

StreamingXXHash32 hash32 = factory.newStreamingHash32(seed);

byte[] buf = new byte[8]; // for real-world usage, use a larger buffer, like 8192 bytes

for (;;) {

  int read = in.read(buf);

  if (read == -1) {

    break;

  }

  hash32.update(buf, 0, read);

}

int hash = hash32.getValue();

```



# Download



You can download released artifacts from [Maven Central](https://search.maven.org/search?q=g:org.lz4%20a:lz4-java).



You can download pure-Java lz4-java from [Maven Central](https://search.maven.org/search?q=g:org.lz4%20a:lz4-pure-java). These artifacts include the Safe and Unsafe Java versions but not JNI bindings. (Experimental)



# Documentation



 - [lz4](https://lz4.github.io/lz4-java/1.8.0/docs/net/jpountz/lz4/package-summary.html)

 - [xxhash](https://lz4.github.io/lz4-java/1.8.0/docs/net/jpountz/xxhash/package-summary.html)

 - [changelog](https://github.com/lz4/lz4-java/blob/master/CHANGES.md)



# Performance



Both lz4 and xxhash focus on speed. Although compression, decompression and

hashing performance can depend a lot on the input (there are lies, damn lies

and benchmarks), here are some benchmarks that try to give a sense of the

speed at which they compress/decompress/hash bytes.



 - [lz4 compression](https://lz4.github.io/lz4-java/1.8.0/lz4-compression-benchmark/)

 - [lz4 decompression](https://lz4.github.io/lz4-java/1.8.0/lz4-decompression-benchmark/)

 - [xxhash hashing](https://lz4.github.io/lz4-java/1.3.0/xxhash-benchmark/)



# Build



## Requirements



 - JDK version 7 or newer,

 - ant version 1.10.2 or newer,

 - ivy.



If ivy is not installed yet, ant can take care of it for you, just run

`ant ivy-bootstrap`. The library will be installed under ${user.home}/.ant/lib.



You might hit an error like the following when the ivy in ${user.home}/.ant/lib is old. You can delete it and then run `ant ivy-bootstrap` again to install the latest version.

```

[ivy:resolve] 		::::::::::::::::::::::::::::::::::::::::::::::

[ivy:resolve] 		::          UNRESOLVED DEPENDENCIES         ::

[ivy:resolve] 		::::::::::::::::::::::::::::::::::::::::::::::

```



## Instructions



For lz4-java 1.5.0 or newer, first run `git submodule init` and then `git submodule update`

to initialize the `lz4` submodule in `src/lz4`.



Then run `ant`. It will:



 - generate some Java source files in `build/java` from the templates that are

   located under `src/build`,

 - compile the lz4 and xxhash libraries and their JNI (Java Native Interface)

   bindings,

 - compile Java sources in `src/java` (normal sources), `src/java-unsafe`

   (sources that make use of `sun.misc.Unsafe`) and `build/java`

   (auto-generated sources) to `build/classes`, `build/unsafe-classes` and

   `build/generated-classes`,

 - generate a JAR file called lz4-${version}.jar under the `dist` directory.



The JAR file that is generated contains Java class files, the native library

and the JNI bindings. If you add this JAR to your classpath, the native library

will be copied to a temporary directory and dynamically linked to your Java

application.