How to use LZMA SDK to compress/decompress in Java

问题:

http://www.7-zip.org/sdk.html This site provide a LZMA SDK for compress/decompress files, I would like to give it a shot but I am lost.

Anyone got experience on this? Or a tutorial? Thanks.

回答1:

Short answer: don't

The 7zip sdk is old and unmaintained and it's just a JNI wrapper around the C++ library. A pure Java implementation on a modern JVM (1.7+) is as fast as a C++ one and has less dependecies and portability issues.

Have a look at http://tukaani.org/xz/java.html

XZ is a file format based on LZMA2 (an improved version of LZMA)

The guys that invented the XZ format build a pure java implementation of the XZ archive compression / extraction algorithms

The XZ file format is designed to store 1 file only. Thus you need to zip/tar the source folder(s) into a single uncompressed file first.

Using the java library is as easy as this:

FileInputStream inFile = new FileInputStream("src.tar");
FileOutputStream outfile = new FileOutputStream("src.tar.xz");

LZMA2Options options = new LZMA2Options();

options.setPreset(7); // play with this number: 6 is default but 7 works better for mid sized archives ( > 8mb)

XZOutputStream out = new XZOutputStream(outfile, options);

byte[] buf = new byte[8192];
int size;
while ((size = inFile.read(buf)) != -1)
   out.write(buf, 0, size);

out.finish();

回答2:

Check out the LzmaAlone.java and LzmaBench.java files in the Java/SevenZip folder of the zip file from that link you posted.

回答3:

Use J7Zip. Its a java port of the LZMA SDK. You find it here:

http://sourceforge.net/projects/p7zip/files/J7Zip/

alternative

Use the lzmajio.jar with LzmaInputStream and LzmaOutputStream classes

you find it on github:

http://github.com/league/lzmajio/downloads

回答4:

You can use this library instead. It is "outdated" but still works fine.

Maven dependency

<dependency>
    <groupId>com.github.jponge</groupId>
    <artifactId>lzma-java</artifactId>
    <version>1.2</version>
</dependency>

Utility class

import lzma.sdk.lzma.Decoder;
import lzma.streams.LzmaInputStream;
import lzma.streams.LzmaOutputStream;
import org.apache.commons.compress.utils.IOUtils;

import java.io.*;
import java.nio.file.Path;

public class LzmaCompressor
{
    private Path rawFilePath;
    private Path compressedFilePath;

    public LzmaCompressor(Path rawFilePath, Path compressedFilePath)
    {
        this.rawFilePath = rawFilePath;
        this.compressedFilePath = compressedFilePath;
    }

    public void compress() throws IOException
    {
        try (LzmaOutputStream outputStream = new LzmaOutputStream.Builder(
                new BufferedOutputStream(new FileOutputStream(compressedFilePath.toFile())))
                .useMaximalDictionarySize()
                .useMaximalFastBytes()
                .build();
             InputStream inputStream = new BufferedInputStream(new FileInputStream(rawFilePath.toFile())))
        {
            IOUtils.copy(inputStream, outputStream);
        }
    }

    public void decompress() throws IOException
    {
        try (LzmaInputStream inputStream = new LzmaInputStream(
                new BufferedInputStream(new FileInputStream(compressedFilePath.toFile())),
                new Decoder());
             OutputStream outputStream = new BufferedOutputStream(
                     new FileOutputStream(rawFilePath.toFile())))
        {
            IOUtils.copy(inputStream, outputStream);
        }
    }
}

Firstly you have to create a file with content to start compressing. You can use this website to generate random text.

Example compression and decompression

Path rawFile = Paths.get("raw.txt");
Path compressedFile = Paths.get("compressed.lzma");

LzmaCompressor lzmaCompressor = new LzmaCompressor(rawFile, compressedFile);
lzmaCompressor.compress();
lzmaCompressor.decompress();

回答5:

Here are tested examples of using XZ Utils pure java library to pack and unpack XZ archives with LZMA2 compression algorithm with great ratio.

import org.tukaani.xz.*;

// CompressXz
public static void main(String[] args) throws Exception {
    String from = args[0];
    String to = args[1];
    try (FileOutputStream fileStream = new FileOutputStream(to);
         XZOutputStream xzStream = new XZOutputStream(
                 fileStream, new LZMA2Options(LZMA2Options.PRESET_MAX), BasicArrayCache.getInstance())) {

        Files.copy(Paths.get(from), xzStream);
    }
}

// DecompressXz
public static void main(String[] args) throws Exception {
    String from = args[0];
    String to = args[1];
    try (FileInputStream fileStream = new FileInputStream(from);
         XZInputStream xzStream = new XZInputStream(fileStream, BasicArrayCache.getInstance())) {

        Files.copy(xzStream, Paths.get(to), StandardCopyOption.REPLACE_EXISTING);
    }
}

// DecompressXzSeekable (partial)
public static void main(String[] args) throws Exception {
    String from = args[0];
    String to = args[1];
    int offset = Integer.parseInt(args[2]);
    int size = Integer.parseInt(args[3]);
    try (SeekableInputStream fileStream = new SeekableFileInputStream(from);
         SeekableXZInputStream xzStream = new SeekableXZInputStream(fileStream, BasicArrayCache.getInstance())) {

        xzStream.seek(offset);
        byte[] buf = new byte[size];
        if (size != xzStream.read(buf)) {
            xzStream.available(); // let it throw the last exception, if any
            throw new IOException("Truncated stream");
        }
        Files.write(Paths.get(to), buf);
    }
}