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<document>
  <properties>
    <title>Commons Compress User Guide</title>
    <author email="dev@commons.apache.org">Commons Documentation Team</author>
  </properties>
  <body>
    <section name="General Notes">

      <subsection name="Archivers and Compressors">
        <p>Commons Compress calls all formats that compress a single
        stream of data compressor formats while all formats that
        collect multiple entries inside a single (potentially
        compressed) archive are archiver formats.</p>

        <p>The compressor formats supported are gzip, bzip2, xz, lzma,
        Pack200, DEFLATE, Brotli, DEFLATE64, ZStandard and Z, the archiver formats are 7z, ar, arj,
        cpio, dump, tar and zip.  Pack200 is a special case as it can
        only compress JAR files.</p>

        <p>We currently only provide read support for arj,
        dump, Brotli, DEFLATE64 and Z.  arj can only read uncompressed archives, 7z can read
        archives with many compression and encryption algorithms
        supported by 7z but doesn't support encryption when writing
        archives.</p>
      </subsection>

      <subsection name="Buffering">
        <p>The stream classes all wrap around streams provided by the
          calling code and they work on them directly without any
          additional buffering.  On the other hand most of them will
          benefit from buffering so it is highly recommended that
          users wrap their stream
          in <code>Buffered<em>(In|Out)</em>putStream</code>s before
          using the Commons Compress API.</p>

      </subsection>

      <subsection name="Factories">

        <p>Compress provides factory methods to create input/output
          streams based on the names of the compressor or archiver
          format as well as factory methods that try to guess the
          format of an input stream.</p>

        <p>To create a compressor writing to a given output by using
          the algorithm name:</p>
        <source><![CDATA[
CompressorOutputStream gzippedOut = new CompressorStreamFactory()
    .createCompressorOutputStream(CompressorStreamFactory.GZIP, myOutputStream);
]]></source>

        <p>Make the factory guess the input format for a given
        archiver stream:</p>
        <source><![CDATA[
ArchiveInputStream input = new ArchiveStreamFactory()
    .createArchiveInputStream(originalInput);
]]></source>

        <p>Make the factory guess the input format for a given
        compressor stream:</p>
        <source><![CDATA[
CompressorInputStream input = new CompressorStreamFactory()
    .createCompressorInputStream(originalInput);
]]></source>

        <p>Note that there is no way to detect the lzma or Brotli formats so only
        the two-arg version of
        <code>createCompressorInputStream</code> can be used.  Prior
        to Compress 1.9 the .Z format hasn't been auto-detected
        either.</p>

      </subsection>

      <subsection name="Restricting Memory Usage">
        <p>Starting with Compress 1.14
        <code>CompressorStreamFactory</code> has an optional
        constructor argument that can be used to set an upper limit of
        memory that may be used while decompressing or compressing a
        stream. As of 1.14 this setting only affects decompressing Z,
        XZ and LZMA compressed streams.</p>
        <p>Since Compress 1.19 <code>SevenZFile</code> also has an
        optional constructor to pass an upper memory limit which is supported
        in LZMA compressed streams. Since Compress 1.21 this setting
        also is taken into account when reading the metadata of an archive.</p>
        <p>For the Snappy and LZ4 formats the amount of memory used
        during compression is directly proportional to the window
        size.</p>
      </subsection>

      <subsection name="Statistics">
        <p>Starting with Compress 1.17 most of the
        <code>CompressorInputStream</code> implementations as well as
        <code>ZipArchiveInputStream</code> and all streams returned by
        <code>ZipFile.getInputStream</code> implement the
        <code>InputStreamStatistics</code>
        interface. <code>SevenZFile</code> provides statistics for the
        current entry via the
        <code>getStatisticsForCurrentEntry</code> method. This
        interface can be used to track progress while extracting a
        stream or to detect potential <a
        href="https://en.wikipedia.org/wiki/Zip_bomb">zip bombs</a>
        when the compression ratio becomes suspiciously large.</p>
      </subsection>

    </section>
    <section name="Archivers">

      <subsection name="Unsupported Features">
        <p>Many of the supported formats have developed different
        dialects and extensions and some formats allow for features
        (not yet) supported by Commons Compress.</p>

        <p>The <code>ArchiveInputStream</code> class provides a method
        <code>canReadEntryData</code> that will return false if
        Commons Compress can detect that an archive uses a feature
        that is not supported by the current implementation.  If it
        returns false you should not try to read the entry but skip
        over it.</p>

      </subsection>

      <subsection name="Entry Names">
        <p>All archive formats provide meta data about the individual
        archive entries via instances of <code>ArchiveEntry</code> (or
        rather subclasses of it). When reading from an archive the
        information provided the <code>getName</code> method is the
        raw name as stored inside of the archive. There is no
        guarantee the name represents a relative file name or even a
        valid file name on your target operating system at all. You
        should double check the outcome when you try to create file
        names from entry names.</p>
      </subsection>

      <subsection name="Common Extraction Logic">
        <p>Apart from 7z all formats provide a subclass of
        <code>ArchiveInputStream</code> that can be used to create an
        archive. For 7z <code>SevenZFile</code> provides a similar API
        that does not represent a stream as our implementation
        requires random access to the input and cannot be used for
        general streams. The ZIP implementation can benefit a lot from
        random access as well, see the <a
        href="zip.html#ZipArchiveInputStream_vs_ZipFile">zip
        page</a> for details.</p>

        <p>Assuming you want to extract an archive to a target
        directory you'd call <code>getNextEntry</code>, verify the
        entry can be read, construct a sane file name from the entry's
        name, create a <code>File</code> and write all contents to
        it - here <code>IOUtils.copy</code> may come handy. You do so
        for every entry until <code>getNextEntry</code> returns
        <code>null</code>.</p>

        <p>A skeleton might look like:</p>

        <source><![CDATA[
File targetDir = ...
try (ArchiveInputStream i = ... create the stream for your format, use buffering...) {
    ArchiveEntry entry = null;
    while ((entry = i.getNextEntry()) != null) {
        if (!i.canReadEntryData(entry)) {
            // log something?
            continue;
        }
        String name = fileName(targetDir, entry);
        File f = new File(name);
        if (entry.isDirectory()) {
            if (!f.isDirectory() && !f.mkdirs()) {
                throw new IOException("failed to create directory " + f);
            }
        } else {
            File parent = f.getParentFile();
            if (!parent.isDirectory() && !parent.mkdirs()) {
                throw new IOException("failed to create directory " + parent);
            }
            try (OutputStream o = Files.newOutputStream(f.toPath())) {
                IOUtils.copy(i, o);
            }
        }
    }
}
]]></source>

        <p>where the hypothetical <code>fileName</code> method is
        written by you and provides the absolute name for the file
        that is going to be written on disk. Here you should perform
        checks that ensure the resulting file name actually is a valid
        file name on your operating system or belongs to a file inside
        of <code>targetDir</code> when using the entry's name as
        input.</p>

        <p>If you want to combine an archive format with a compression
        format - like when reading a "tar.gz" file - you wrap the
        <code>ArchiveInputStream</code> around
        <code>CompressorInputStream</code> for example:</p>

        <source><![CDATA[
try (InputStream fi = Files.newInputStream(Paths.get("my.tar.gz"));
     InputStream bi = new BufferedInputStream(fi);
     InputStream gzi = new GzipCompressorInputStream(bi);
     ArchiveInputStream o = new TarArchiveInputStream(gzi)) {
}
]]></source>

      </subsection>

      <subsection name="Common Archival Logic">
        <p>Apart from 7z all formats that support writing provide a
        subclass of <code>ArchiveOutputStream</code> that can be used
        to create an archive. For 7z <code>SevenZOutputFile</code>
        provides a similar API that does not represent a stream as our
        implementation requires random access to the output and cannot
        be used for general streams. The
        <code>ZipArchiveOutputStream</code> class will benefit from
        random access as well but can be used for non-seekable streams
        - but not all features will be available and the archive size
        might be slightly bigger, see <a
        href="zip.html#ZipArchiveOutputStream">the zip page</a> for
        details.</p>

        <p>Assuming you want to add a collection of files to an
        archive, you can first use <code>createArchiveEntry</code> for
        each file. In general this will set a few flags (usually the
        last modified time, the size and the information whether this
        is a file or directory) based on the <code>File</code> or <code>Path</code>
        instance. Alternatively you can create the
        <code>ArchiveEntry</code> subclass corresponding to your
        format directly. Often you may want to set additional flags
        like file permissions or owner information before adding the
        entry to the archive.</p>

        <p>Next you use <code>putArchiveEntry</code> in order to add
        the entry and then start using <code>write</code> to add the
        content of the entry - here <code>IOUtils.copy</code> may
        come handy. Finally you invoke
        <code>closeArchiveEntry</code> once you've written all content
        and before you add the next entry.</p>

        <p>Once all entries have been added you'd invoke
        <code>finish</code> and finally <code>close</code> the
        stream.</p>

        <p>A skeleton might look like:</p>

        <source><![CDATA[
Collection<File> filesToArchive = ...
try (ArchiveOutputStream o = ... create the stream for your format ...) {
    for (File f : filesToArchive) {
        // maybe skip directories for formats like AR that don't store directories
        ArchiveEntry entry = o.createArchiveEntry(f, entryName(f));
        // potentially add more flags to entry
        o.putArchiveEntry(entry);
        if (f.isFile()) {
            try (InputStream i = Files.newInputStream(f.toPath())) {
                IOUtils.copy(i, o);
            }
        }
        o.closeArchiveEntry();
    }
    o.finish();
}
]]></source>

        <p>where the hypothetical <code>entryName</code> method is
        written by you and provides the name for the entry as it is
        going to be written to the archive.</p>

        <p>If you want to combine an archive format with a compression
        format - like when creating a "tar.gz" file - you wrap the
        <code>ArchiveOutputStream</code> around a
        <code>CompressorOutputStream</code> for example:</p>

        <source><![CDATA[
try (OutputStream fo = Files.newOutputStream(Paths.get("my.tar.gz"));
     OutputStream gzo = new GzipCompressorOutputStream(fo);
     ArchiveOutputStream o = new TarArchiveOutputStream(gzo)) {
}
]]></source>

      </subsection>

      <subsection name="7z">

        <p>Note that Commons Compress currently only supports a subset
        of compression and encryption algorithms used for 7z archives.
        For writing only uncompressed entries, LZMA, LZMA2, BZIP2 and
        Deflate are supported - in addition to those reading supports
        AES-256/SHA-256 and DEFLATE64.</p>

        <p>Writing multipart archives is not supported at
        all. Multipart archives can be read by concatenating the parts
        for example by using
        <code>MultiReadOnlySeekableByteChannel</code>.</p>

        <p>7z archives can use multiple compression and encryption
        methods as well as filters combined as a pipeline of methods
        for its entries.  Prior to Compress 1.8 you could only specify
        a single method when creating archives - reading archives
        using more than one method has been possible before.  Starting
        with Compress 1.8 it is possible to configure the full
        pipeline using the <code>setContentMethods</code> method of
        <code>SevenZOutputFile</code>.  Methods are specified in the
        order they appear inside the pipeline when creating the
        archive, you can also specify certain parameters for some of
        the methods - see the Javadocs of
        <code>SevenZMethodConfiguration</code> for details.</p>

        <p>When reading entries from an archive the
        <code>getContentMethods</code> method of
        <code>SevenZArchiveEntry</code> will properly represent the
        compression/encryption/filter methods but may fail to
        determine the configuration options used.  As of Compress 1.8
        only the dictionary size used for LZMA2 can be read.</p>

        <p>Currently solid compression - compressing multiple files
        as a single block to benefit from patterns repeating across
        files - is only supported when reading archives.  This also
        means compression ratio will likely be worse when using
        Commons Compress compared to the native 7z executable.</p>

        <p>Reading or writing requires a
        <code>SeekableByteChannel</code> that will be obtained
        transparently when reading from or writing to a file. The
        class
        <code>org.apache.commons.compress.utils.SeekableInMemoryByteChannel</code>
        allows you to read from or write to an in-memory archive.</p>

        <p>Some 7z archives don't contain any names for the archive
        entries. The native 7zip tools derive a default name from the
        name of the archive itself for such entries. Starting with
        Compress 1.19 <code>SevenZFile</code> has an option to mimic
        this behavior, but by default unnamed archive entries will
        return <code>null</code> from
        <code>SevenZArchiveEntry#getName</code>.</p>

        <p>Adding an entry to a 7z archive:</p>
<source><![CDATA[
SevenZOutputFile sevenZOutput = new SevenZOutputFile(file);
SevenZArchiveEntry entry = sevenZOutput.createArchiveEntry(fileToArchive, name);
sevenZOutput.putArchiveEntry(entry);
sevenZOutput.write(contentOfEntry);
sevenZOutput.closeArchiveEntry();
]]></source>

        <p>Uncompressing a given 7z archive (you would
          certainly add exception handling and make sure all streams
          get closed properly):</p>
<source><![CDATA[
SevenZFile sevenZFile = new SevenZFile(new File("archive.7z"));
SevenZArchiveEntry entry = sevenZFile.getNextEntry();
byte[] content = new byte[entry.getSize()];
LOOP UNTIL entry.getSize() HAS BEEN READ {
    sevenZFile.read(content, offset, content.length - offset);
}
]]></source>

          <p>Uncompressing a given in-memory 7z archive:</p>
          <source><![CDATA[
byte[] inputData; // 7z archive contents
SeekableInMemoryByteChannel inMemoryByteChannel = new SeekableInMemoryByteChannel(inputData);
SevenZFile sevenZFile = new SevenZFile(inMemoryByteChannel);
SevenZArchiveEntry entry = sevenZFile.getNextEntry();
sevenZFile.read();  // read current entry's data
]]></source>

          <h4><a name="Encrypted 7z Archives"></a>Encrypted 7z Archives</h4>

          <p>Currently Compress supports reading but not writing of
          encrypted archives. When reading an encrypted archive a
          password has to be provided to one of
          <code>SevenZFile</code>'s constructors. If you try to read
          an encrypted archive without specifying a password a
          <code>PasswordRequiredException</code> (a subclass of
          <code>IOException</code>) will be thrown.</p>

          <p>When specifying the password as a <code>byte[]</code> one
          common mistake is to use the wrong encoding when creating
          the <code>byte[]</code> from a <code>String</code>. The
          <code>SevenZFile</code> class expects the bytes to
          correspond to the UTF16-LE encoding of the password. An
          example of reading an encrypted archive is</p>

<source><![CDATA[
SevenZFile sevenZFile = new SevenZFile(new File("archive.7z"), "secret".getBytes(StandardCharsets.UTF_16LE));
SevenZArchiveEntry entry = sevenZFile.getNextEntry();
byte[] content = new byte[entry.getSize()];
LOOP UNTIL entry.getSize() HAS BEEN READ {
    sevenZFile.read(content, offset, content.length - offset);
}
]]></source>

        <p>Starting with Compress 1.17 new constructors have been
        added that accept the password as <code>char[]</code> rather
        than a <code>byte[]</code>. We recommend you use these in
        order to avoid the problem above.</p>

<source><![CDATA[
SevenZFile sevenZFile = new SevenZFile(new File("archive.7z"), "secret".toCharArray());
SevenZArchiveEntry entry = sevenZFile.getNextEntry();
byte[] content = new byte[entry.getSize()];
LOOP UNTIL entry.getSize() HAS BEEN READ {
    sevenZFile.read(content, offset, content.length - offset);
}
]]></source>

        <h4><a name="Random-Access to 7z Archives"></a>Random-Access to 7z Archives</h4>

        <p>Prior to Compress 1.20 7z archives could only be read
        sequentially. The
        <code>getInputStream(SevenZArchiveEntry)</code> method
        introduced with Compress 1.20 now provides random access but
        at least when the archive uses solid compression random access
        will likely be significantly slower than sequential
        access.</p>

        <h4><a name="Recovering from Certain Broken 7z Archives"></a>Recovering from Certain Broken 7z Archives</h4>

        <p>Starting with Compress 1.19 <code>SevenZFile</code> tries
        to recover archives that look as if they were part of a
        multi-volume archive where the first volume has been removed
        too early.</p>

        <p>Starting with Compress 1.21 this option has to be enabled
        explicitly in <code>SevenZFileOptions</code>. The way recovery
        works is by Compress scanning an archive from the end for
        something that might look like valid 7z metadata and use that,
        if it can successfully parse the block of data. When doing so
        Compress may encounter blocks of metadata that look like the
        metadata of very large archives which in turn may make
        Compress allocate a lot of memory. Therefore we strongly
        recommend you also set a memory limit inside the
        <code>SevenZFileOptions</code> if you enable recovery.</p>
      </subsection>

      <subsection name="ar">

        <p>In addition to the information stored
          in <code>ArchiveEntry</code> a <code>ArArchiveEntry</code>
          stores information about the owner user and group as well as
          Unix permissions.</p>

        <p>Adding an entry to an ar archive:</p>
<source><![CDATA[
ArArchiveEntry entry = new ArArchiveEntry(name, size);
arOutput.putArchiveEntry(entry);
arOutput.write(contentOfEntry);
arOutput.closeArchiveEntry();
]]></source>

        <p>Reading entries from an ar archive:</p>
<source><![CDATA[
ArArchiveEntry entry = (ArArchiveEntry) arInput.getNextEntry();
byte[] content = new byte[entry.getSize()];
LOOP UNTIL entry.getSize() HAS BEEN READ {
    arInput.read(content, offset, content.length - offset);
}
]]></source>

        <p>Traditionally the AR format doesn't allow file names longer
          than 16 characters.  There are two variants that circumvent
          this limitation in different ways, the GNU/SRV4 and the BSD
          variant.  Commons Compress 1.0 to 1.2 can only read archives
          using the GNU/SRV4 variant, support for the BSD variant has
          been added in Commons Compress 1.3.  Commons Compress 1.3
          also optionally supports writing archives with file names
          longer than 16 characters using the BSD dialect, writing
          the SVR4/GNU dialect is not supported.</p>

        <table>
          <thead>
            <tr>
              <th>Version of Apache Commons Compress</th>
              <th>Support for Traditional AR Format</th>
              <th>Support for GNU/SRV4 Dialect</th>
              <th>Support for BSD Dialect</th>
            </tr>
          </thead>
          <tbody>
            <tr>
              <td>1.0 to 1.2</td>
              <td>read/write</td>
              <td>read</td>
              <td>-</td>
            </tr>
            <tr>
              <td>1.3 and later</td>
              <td>read/write</td>
              <td>read</td>
              <td>read/write</td>
            </tr>
          </tbody>
        </table>

        <p>It is not possible to detect the end of an AR archive in a
        reliable way so <code>ArArchiveInputStream</code> will read
        until it reaches the end of the stream or fails to parse the
        stream's content as AR entries.</p>

      </subsection>

      <subsection name="arj">

        <p>Note that Commons Compress doesn't support compressed,
        encrypted or multi-volume ARJ archives, yet.</p>

        <p>Uncompressing a given arj archive (you would
          certainly add exception handling and make sure all streams
          get closed properly):</p>
<source><![CDATA[
ArjArchiveEntry entry = arjInput.getNextEntry();
byte[] content = new byte[entry.getSize()];
LOOP UNTIL entry.getSize() HAS BEEN READ {
    arjInput.read(content, offset, content.length - offset);
}
]]></source>
      </subsection>

      <subsection name="cpio">

        <p>In addition to the information stored
          in <code>ArchiveEntry</code> a <code>CpioArchiveEntry</code>
          stores various attributes including information about the
          original owner and permissions.</p>

        <p>The cpio package supports the "new portable" as well as the
          "old" format of CPIO archives in their binary, ASCII and
          "with CRC" variants.</p>

        <p>Adding an entry to a cpio archive:</p>
<source><![CDATA[
CpioArchiveEntry entry = new CpioArchiveEntry(name, size);
cpioOutput.putArchiveEntry(entry);
cpioOutput.write(contentOfEntry);
cpioOutput.closeArchiveEntry();
]]></source>

        <p>Reading entries from an cpio archive:</p>
<source><![CDATA[
CpioArchiveEntry entry = cpioInput.getNextCPIOEntry();
byte[] content = new byte[entry.getSize()];
LOOP UNTIL entry.getSize() HAS BEEN READ {
    cpioInput.read(content, offset, content.length - offset);
}
]]></source>

        <p>Traditionally CPIO archives are written in blocks of 512
        bytes - the block size is a configuration parameter of the
        <code>Cpio*Stream</code>'s constructors.  Starting with version
        1.5 <code>CpioArchiveInputStream</code> will consume the
        padding written to fill the current block when the end of the
        archive is reached.  Unfortunately many CPIO implementations
        use larger block sizes so there may be more zero-byte padding
        left inside the original input stream after the archive has
        been consumed completely.</p>

      </subsection>

      <subsection name="jar">
        <p>In general, JAR archives are ZIP files, so the JAR package
          supports all options provided by the <a href="#zip">ZIP</a> package.</p>

        <p>To be interoperable JAR archives should always be created
          using the UTF-8 encoding for file names (which is the
          default).</p>

        <p>Archives created using <code>JarArchiveOutputStream</code>
          will implicitly add a <code>JarMarker</code> extra field to
          the very first archive entry of the archive which will make
          Solaris recognize them as Java archives and allows them to
          be used as executables.</p>

        <p>Note that <code>ArchiveStreamFactory</code> doesn't
          distinguish ZIP archives from JAR archives, so if you use
          the one-argument <code>createArchiveInputStream</code>
          method on a JAR archive, it will still return the more
          generic <code>ZipArchiveInputStream</code>.</p>

        <p>The <code>JarArchiveEntry</code> class contains fields for
          certificates and attributes that are planned to be supported
          in the future but are not supported as of Compress 1.0.</p>

        <p>Adding an entry to a jar archive:</p>
<source><![CDATA[
JarArchiveEntry entry = new JarArchiveEntry(name, size);
entry.setSize(size);
jarOutput.putArchiveEntry(entry);
jarOutput.write(contentOfEntry);
jarOutput.closeArchiveEntry();
]]></source>

        <p>Reading entries from an jar archive:</p>
<source><![CDATA[
JarArchiveEntry entry = jarInput.getNextJarEntry();
byte[] content = new byte[entry.getSize()];
LOOP UNTIL entry.getSize() HAS BEEN READ {
    jarInput.read(content, offset, content.length - offset);
}
]]></source>
      </subsection>

      <subsection name="dump">

        <p>In addition to the information stored
          in <code>ArchiveEntry</code> a <code>DumpArchiveEntry</code>
          stores various attributes including information about the
          original owner and permissions.</p>

        <p>As of Commons Compress 1.3 only dump archives using the
          new-fs format - this is the most common variant - are
          supported.  Right now this library supports uncompressed and
          ZLIB compressed archives and can not write archives at
          all.</p>

        <p>Reading entries from an dump archive:</p>
<source><![CDATA[
DumpArchiveEntry entry = dumpInput.getNextDumpEntry();
byte[] content = new byte[entry.getSize()];
LOOP UNTIL entry.getSize() HAS BEEN READ {
    dumpInput.read(content, offset, content.length - offset);
}
]]></source>

        <p>Prior to version 1.5 <code>DumpArchiveInputStream</code>
        would close the original input once it had read the last
        record.  Starting with version 1.5 it will not close the
        stream implicitly.</p>

      </subsection>

      <subsection name="tar">

        <p>The TAR package has a <a href="tar.html">dedicated
            documentation page</a>.</p>

        <p>Adding an entry to a tar archive:</p>
<source><![CDATA[
TarArchiveEntry entry = new TarArchiveEntry(name);
entry.setSize(size);
tarOutput.putArchiveEntry(entry);
tarOutput.write(contentOfEntry);
tarOutput.closeArchiveEntry();
]]></source>

        <p>Reading entries from an tar archive:</p>
<source><![CDATA[
TarArchiveEntry entry = tarInput.getNextTarEntry();
byte[] content = new byte[entry.getSize()];
LOOP UNTIL entry.getSize() HAS BEEN READ {
    tarInput.read(content, offset, content.length - offset);
}
]]></source>
      </subsection>

      <subsection name="zip">
        <p>The ZIP package has a <a href="zip.html">dedicated
            documentation page</a>.</p>

        <p>Adding an entry to a zip archive:</p>
<source><![CDATA[
ZipArchiveEntry entry = new ZipArchiveEntry(name);
entry.setSize(size);
zipOutput.putArchiveEntry(entry);
zipOutput.write(contentOfEntry);
zipOutput.closeArchiveEntry();
]]></source>

        <p><code>ZipArchiveOutputStream</code> can use some internal
          optimizations exploiting <code>SeekableByteChannel</code> if it
          knows it is writing to a seekable output rather than a non-seekable
          stream.  If you are writing to a file, you should use the
          constructor that accepts a <code>File</code> or
          <code>SeekableByteChannel</code> argument rather
          than the one using an <code>OutputStream</code> or the
          factory method in <code>ArchiveStreamFactory</code>.</p>

        <p>Reading entries from an zip archive:</p>
<source><![CDATA[
ZipArchiveEntry entry = zipInput.getNextZipEntry();
byte[] content = new byte[entry.getSize()];
LOOP UNTIL entry.getSize() HAS BEEN READ {
    zipInput.read(content, offset, content.length - offset);
}
]]></source>

        <p>Reading entries from an zip archive using the
          recommended <code>ZipFile</code> class:</p>
<source><![CDATA[
ZipArchiveEntry entry = zipFile.getEntry(name);
InputStream content = zipFile.getInputStream(entry);
try {
    READ UNTIL content IS EXHAUSTED
} finally {
    content.close();
}
]]></source>

          <p>Reading entries from an in-memory zip archive using
              <code>SeekableInMemoryByteChannel</code> and <code>ZipFile</code> class:</p>
<source><![CDATA[
byte[] inputData; // zip archive contents
SeekableInMemoryByteChannel inMemoryByteChannel = new SeekableInMemoryByteChannel(inputData);
ZipFile zipFile = new ZipFile(inMemoryByteChannel);
ZipArchiveEntry archiveEntry = zipFile.getEntry("entryName");
InputStream inputStream = zipFile.getInputStream(archiveEntry);
inputStream.read() // read data from the input stream
]]></source>

          <p>Creating a zip file with multiple threads:</p>

          A simple implementation to create a zip file might look like this:

<source><![CDATA[
public class ScatterSample {

  ParallelScatterZipCreator scatterZipCreator = new ParallelScatterZipCreator();
  ScatterZipOutputStream dirs = ScatterZipOutputStream.fileBased(File.createTempFile("scatter-dirs", "tmp"));

  public ScatterSample() throws IOException {
  }

  public void addEntry(ZipArchiveEntry zipArchiveEntry, InputStreamSupplier streamSupplier) throws IOException {
     if (zipArchiveEntry.isDirectory() && !zipArchiveEntry.isUnixSymlink())
        dirs.addArchiveEntry(ZipArchiveEntryRequest.createZipArchiveEntryRequest(zipArchiveEntry, streamSupplier));
     else
        scatterZipCreator.addArchiveEntry( zipArchiveEntry, streamSupplier);
  }

  public void writeTo(ZipArchiveOutputStream zipArchiveOutputStream)
  throws IOException, ExecutionException, InterruptedException {
     dirs.writeTo(zipArchiveOutputStream);
     dirs.close();
     scatterZipCreator.writeTo(zipArchiveOutputStream);
  }
}
]]></source>
      </subsection>

    </section>
    <section name="Compressors">

      <subsection name="Concatenated Streams">
        <p>For the bzip2, gzip and xz formats as well as the framed
        lz4 format a single compressed file
        may actually consist of several streams that will be
        concatenated by the command line utilities when decompressing
        them.  Starting with Commons Compress 1.4 the
        <code>*CompressorInputStream</code>s for these formats support
        concatenating streams as well, but they won't do so by
        default.  You must use the two-arg constructor and explicitly
        enable the support.</p>
      </subsection>

      <subsection name="Brotli">

        <p>The implementation of this package is provided by the
          <a href="https://github.com/google/brotli">Google Brotli dec</a> library.</p>

        <p>Uncompressing a given Brotli compressed file (you would
          certainly add exception handling and make sure all streams
          get closed properly):</p>
<source><![CDATA[
InputStream fin = Files.newInputStream(Paths.get("archive.tar.br"));
BufferedInputStream in = new BufferedInputStream(fin);
OutputStream out = Files.newOutputStream(Paths.get("archive.tar"));
BrotliCompressorInputStream brIn = new BrotliCompressorInputStream(in);
final byte[] buffer = new byte[buffersize];
int n = 0;
while (-1 != (n = brIn.read(buffer))) {
    out.write(buffer, 0, n);
}
out.close();
brIn.close();
]]></source>
      </subsection>

      <subsection name="bzip2">

        <p>Note that <code>BZipCompressorOutputStream</code> keeps
          hold of some big data structures in memory.  While it is
          recommended for <em>any</em> stream that you close it as soon as
          you no longer need it, this is even more important
          for <code>BZipCompressorOutputStream</code>.</p>

        <p>Uncompressing a given bzip2 compressed file (you would
          certainly add exception handling and make sure all streams
          get closed properly):</p>
<source><![CDATA[
InputStream fin = Files.newInputStream(Paths.get("archive.tar.bz2"));
BufferedInputStream in = new BufferedInputStream(fin);
OutputStream out = Files.newOutputStream(Paths.get("archive.tar"));
BZip2CompressorInputStream bzIn = new BZip2CompressorInputStream(in);
final byte[] buffer = new byte[buffersize];
int n = 0;
while (-1 != (n = bzIn.read(buffer))) {
    out.write(buffer, 0, n);
}
out.close();
bzIn.close();
]]></source>

        <p>Compressing a given file using bzip2 (you would
          certainly add exception handling and make sure all streams
          get closed properly):</p>
<source><![CDATA[
InputStream in = Files.newInputStream(Paths.get("archive.tar"));
OutputStream fout = Files.newOutputStream(Paths.get("archive.tar.bz2"));
BufferedOutputStream out = new BufferedOutputStream(fout);
BZip2CompressorOutputStream bzOut = new BZip2CompressorOutputStream(out);
final byte[] buffer = new byte[buffersize];
int n = 0;
while (-1 != (n = in.read(buffer))) {
    bzOut.write(buffer, 0, n);
}
bzOut.close();
in.close();
]]></source>

      </subsection>

      <subsection name="DEFLATE">

        <p>The implementation of the DEFLATE/INFLATE code used by this
        package is provided by the <code>java.util.zip</code> package
        of the Java class library.</p>

        <p>Uncompressing a given DEFLATE compressed file (you would
          certainly add exception handling and make sure all streams
          get closed properly):</p>
<source><![CDATA[
InputStream fin = Files.newInputStream(Paths.get("some-file"));
BufferedInputStream in = new BufferedInputStream(fin);
OutputStream out = Files.newOutputStream(Paths.get("archive.tar"));
DeflateCompressorInputStream defIn = new DeflateCompressorInputStream(in);
final byte[] buffer = new byte[buffersize];
int n = 0;
while (-1 != (n = defIn.read(buffer))) {
    out.write(buffer, 0, n);
}
out.close();
defIn.close();
]]></source>

        <p>Compressing a given file using DEFLATE (you would
          certainly add exception handling and make sure all streams
          get closed properly):</p>
<source><![CDATA[
InputStream in = Files.newInputStream(Paths.get("archive.tar"));
OutputStream fout = Files.newOutputStream(Paths.get("some-file"));
BufferedOutputStream out = new BufferedOutputStream(fout);
DeflateCompressorOutputStream defOut = new DeflateCompressorOutputStream(out);
final byte[] buffer = new byte[buffersize];
int n = 0;
while (-1 != (n = in.read(buffer))) {
    defOut.write(buffer, 0, n);
}
defOut.close();
in.close();
]]></source>

      </subsection>

      <subsection name="DEFLATE64">

        <p>Uncompressing a given DEFLATE64 compressed file (you would
          certainly add exception handling and make sure all streams
          get closed properly):</p>
<source><![CDATA[
InputStream fin = Files.newInputStream(Paths.get("some-file"));
BufferedInputStream in = new BufferedInputStream(fin);
OutputStream out = Files.newOutputStream(Paths.get("archive.tar"));
Deflate64CompressorInputStream defIn = new Deflate64CompressorInputStream(in);
final byte[] buffer = new byte[buffersize];
int n = 0;
while (-1 != (n = defIn.read(buffer))) {
    out.write(buffer, 0, n);
}
out.close();
defIn.close();
]]></source>

      </subsection>

      <subsection name="gzip">

        <p>The implementation of the DEFLATE/INFLATE code used by this
        package is provided by the <code>java.util.zip</code> package
        of the Java class library.</p>

        <p>Uncompressing a given gzip compressed file (you would
          certainly add exception handling and make sure all streams
          get closed properly):</p>
<source><![CDATA[
InputStream fin = Files.newInputStream(Paths.get("archive.tar.gz"));
BufferedInputStream in = new BufferedInputStream(fin);
OutputStream out = Files.newOutputStream(Paths.get("archive.tar"));
GzipCompressorInputStream gzIn = new GzipCompressorInputStream(in);
final byte[] buffer = new byte[buffersize];
int n = 0;
while (-1 != (n = gzIn.read(buffer))) {
    out.write(buffer, 0, n);
}
out.close();
gzIn.close();
]]></source>

        <p>Compressing a given file using gzip (you would
          certainly add exception handling and make sure all streams
          get closed properly):</p>
<source><![CDATA[
InputStream in = Files.newInputStream(Paths.get("archive.tar"));
OutputStream fout = Files.newOutputStream(Paths.get("archive.tar.gz"));
BufferedOutputStream out = new BufferedOutputStream(fout);
GzipCompressorOutputStream gzOut = new GzipCompressorOutputStream(out);
final byte[] buffer = new byte[buffersize];
int n = 0;
while (-1 != (n = in.read(buffer))) {
    gzOut.write(buffer, 0, n);
}
gzOut.close();
in.close();
]]></source>

      </subsection>

      <subsection name="LZ4">

        <p>There are two different "formats" used for <a
        href="http://lz4.github.io/lz4/">lz4</a>. The format called
        "block format" only contains the raw compressed data while the
        other provides a higher level "frame format" - Commons
        Compress offers two different stream classes for reading or
        writing either format.</p>

        <p>Uncompressing a given framed LZ4 file (you would
          certainly add exception handling and make sure all streams
          get closed properly):</p>
<source><![CDATA[
InputStream fin = Files.newInputStream(Paths.get("archive.tar.lz4"));
BufferedInputStream in = new BufferedInputStream(fin);
OutputStream out = Files.newOutputStream(Paths.get("archive.tar"));
FramedLZ4CompressorInputStream zIn = new FramedLZ4CompressorInputStream(in);
final byte[] buffer = new byte[buffersize];
int n = 0;
while (-1 != (n = zIn.read(buffer))) {
    out.write(buffer, 0, n);
}
out.close();
zIn.close();
]]></source>

        <p>Compressing a given file using the LZ4 frame format (you would
          certainly add exception handling and make sure all streams
          get closed properly):</p>
<source><![CDATA[
InputStream in = Files.newInputStream(Paths.get("archive.tar"));
OutputStream fout = Files.newOutputStream(Paths.get("archive.tar.lz4"));
BufferedOutputStream out = new BufferedOutputStream(fout);
FramedLZ4CompressorOutputStream lzOut = new FramedLZ4CompressorOutputStream(out);
final byte[] buffer = new byte[buffersize];
int n = 0;
while (-1 != (n = in.read(buffer))) {
    lzOut.write(buffer, 0, n);
}
lzOut.close();
in.close();
]]></source>

      </subsection>

      <subsection name="lzma">

        <p>The implementation of this package is provided by the
          public domain <a href="https://tukaani.org/xz/java.html">XZ
          for Java</a> library.</p>

        <p>Uncompressing a given lzma compressed file (you would
          certainly add exception handling and make sure all streams
          get closed properly):</p>
<source><![CDATA[
InputStream fin = Files.newInputStream(Paths.get("archive.tar.lzma"));
BufferedInputStream in = new BufferedInputStream(fin);
OutputStream out = Files.newOutputStream(Paths.get("archive.tar"));
LZMACompressorInputStream lzmaIn = new LZMACompressorInputStream(in);
final byte[] buffer = new byte[buffersize];
int n = 0;
while (-1 != (n = xzIn.read(buffer))) {
    out.write(buffer, 0, n);
}
out.close();
lzmaIn.close();
]]></source>

        <p>Compressing a given file using lzma (you would
          certainly add exception handling and make sure all streams
          get closed properly):</p>
<source><![CDATA[
InputStream in = Files.newInputStream(Paths.get("archive.tar"));
OutputStream fout = Files.newOutputStream(Paths.get("archive.tar.lzma"));
BufferedOutputStream out = new BufferedOutputStream(fout);
LZMACompressorOutputStream lzOut = new LZMACompressorOutputStream(out);
final byte[] buffer = new byte[buffersize];
int n = 0;
while (-1 != (n = in.read(buffer))) {
    lzOut.write(buffer, 0, n);
}
lzOut.close();
in.close();
]]></source>

      </subsection>

      <subsection name="Pack200">

        <p>The Pack200 package has a <a href="pack200.html">dedicated
          documentation page</a>.</p>

        <p>The implementation of this package used to be provided by
          the <code>java.util.zip</code> package of the Java class
          library. Starting with Compress 1.21 the implementation uses
          a copy of the pack200 code of the now retired Apache
          Harmony&#x2122; project that ships with Compress itself.</p>

        <p>Uncompressing a given pack200 compressed file (you would
          certainly add exception handling and make sure all streams
          get closed properly):</p>
<source><![CDATA[
InputStream fin = Files.newInputStream(Paths.get("archive.pack"));
BufferedInputStream in = new BufferedInputStream(fin);
OutputStream out = Files.newOutputStream(Paths.get("archive.jar"));
Pack200CompressorInputStream pIn = new Pack200CompressorInputStream(in);
final byte[] buffer = new byte[buffersize];
int n = 0;
while (-1 != (n = pIn.read(buffer))) {
    out.write(buffer, 0, n);
}
out.close();
pIn.close();
]]></source>

        <p>Compressing a given jar using pack200 (you would
          certainly add exception handling and make sure all streams
          get closed properly):</p>
<source><![CDATA[
InputStream in = Files.newInputStream(Paths.get("archive.jar"));
OutputStream fout = Files.newOutputStream(Paths.get("archive.pack"));
BufferedOutputStream out = new BufferedInputStream(fout);
Pack200CompressorOutputStream pOut = new Pack200CompressorOutputStream(out);
final byte[] buffer = new byte[buffersize];
int n = 0;
while (-1 != (n = in.read(buffer))) {
    pOut.write(buffer, 0, n);
}
pOut.close();
in.close();
]]></source>

      </subsection>

      <subsection name="Snappy">

        <p>There are two different "formats" used for <a
        href="https://github.com/google/snappy/">Snappy</a>, one only
        contains the raw compressed data while the other provides a
        higher level "framing format" - Commons Compress offers two
        different stream classes for reading either format.</p>

        <p>Starting with 1.12 we've added support for different
        dialects of the framing format that can be specified when
        constructing the stream. The <code>STANDARD</code> dialect
        follows the "framing format" specification while the
        <code>IWORK_ARCHIVE</code> dialect can be used to parse IWA
        files that are part of Apple's iWork 13 format. If no dialect
        has been specified, <code>STANDARD</code> is used. Only the
        <code>STANDARD</code> format can be detected by
        <code>CompressorStreamFactory</code>.</p>

        <p>Uncompressing a given framed Snappy file (you would
          certainly add exception handling and make sure all streams
          get closed properly):</p>
<source><![CDATA[
InputStream fin = Files.newInputStream(Paths.get("archive.tar.sz"));
BufferedInputStream in = new BufferedInputStream(fin);
OutputStream out = Files.newOutputStream(Paths.get("archive.tar"));
FramedSnappyCompressorInputStream zIn = new FramedSnappyCompressorInputStream(in);
final byte[] buffer = new byte[buffersize];
int n = 0;
while (-1 != (n = zIn.read(buffer))) {
    out.write(buffer, 0, n);
}
out.close();
zIn.close();
]]></source>

        <p>Compressing a given file using framed Snappy (you would
          certainly add exception handling and make sure all streams
          get closed properly):</p>
<source><![CDATA[
InputStream in = Files.newInputStream(Paths.get("archive.tar"));
OutputStream fout = Files.newOutputStream(Paths.get("archive.tar.sz"));
BufferedOutputStream out = new BufferedOutputStream(fout);
FramedSnappyCompressorOutputStream snOut = new FramedSnappyCompressorOutputStream(out);
final byte[] buffer = new byte[buffersize];
int n = 0;
while (-1 != (n = in.read(buffer))) {
    snOut.write(buffer, 0, n);
}
snOut.close();
in.close();
]]></source>

      </subsection>

      <subsection name="XZ">

        <p>The implementation of this package is provided by the
          public domain <a href="https://tukaani.org/xz/java.html">XZ
          for Java</a> library.</p>

        <p>When you try to open an XZ stream for reading using
        <code>CompressorStreamFactory</code>, Commons Compress will
        check whether the XZ for Java library is available.  Starting
        with Compress 1.9 the result of this check will be cached
        unless Compress finds OSGi classes in its classpath.  You can
        use <code>XZUtils#setCacheXZAvailability</code> to override
        this default behavior.</p>

        <p>Uncompressing a given XZ compressed file (you would
          certainly add exception handling and make sure all streams
          get closed properly):</p>
<source><![CDATA[
InputStream fin = Files.newInputStream(Paths.get("archive.tar.xz"));
BufferedInputStream in = new BufferedInputStream(fin);
OutputStream out = Files.newOutputStream(Paths.get("archive.tar"));
XZCompressorInputStream xzIn = new XZCompressorInputStream(in);
final byte[] buffer = new byte[buffersize];
int n = 0;
while (-1 != (n = xzIn.read(buffer))) {
    out.write(buffer, 0, n);
}
out.close();
xzIn.close();
]]></source>

        <p>Compressing a given file using XZ (you would
          certainly add exception handling and make sure all streams
          get closed properly):</p>
<source><![CDATA[
InputStream in = Files.newInputStream(Paths.get("archive.tar"));
OutputStream fout = Files.newOutputStream(Paths.get("archive.tar.xz"));
BufferedOutputStream out = new BufferedInputStream(fout);
XZCompressorOutputStream xzOut = new XZCompressorOutputStream(out);
final byte[] buffer = new byte[buffersize];
int n = 0;
while (-1 != (n = in.read(buffer))) {
    xzOut.write(buffer, 0, n);
}
xzOut.close();
in.close();
]]></source>

      </subsection>

      <subsection name="Z">

        <p>Uncompressing a given Z compressed file (you would
          certainly add exception handling and make sure all streams
          get closed properly):</p>
<source><![CDATA[
InputStream fin = Files.newInputStream(Paths.get("archive.tar.Z"));
BufferedInputStream in = new BufferedInputStream(fin);
OutputStream out = Files.newOutputStream(Paths.get("archive.tar"));
ZCompressorInputStream zIn = new ZCompressorInputStream(in);
final byte[] buffer = new byte[buffersize];
int n = 0;
while (-1 != (n = zIn.read(buffer))) {
    out.write(buffer, 0, n);
}
out.close();
zIn.close();
]]></source>

      </subsection>

      <subsection name="Zstandard">

        <p>The implementation of this package is provided by the
          <a href="https://github.com/luben/zstd-jni">Zstandard JNI</a> library.</p>

        <p>Uncompressing a given Zstandard compressed file (you would
          certainly add exception handling and make sure all streams
          get closed properly):</p>
<source><![CDATA[
InputStream fin = Files.newInputStream(Paths.get("archive.tar.zstd"));
BufferedInputStream in = new BufferedInputStream(fin);
OutputStream out = Files.newOutputStream(Paths.get("archive.tar"));
ZstdCompressorInputStream zsIn = new ZstdCompressorInputStream(in);
final byte[] buffer = new byte[buffersize];
int n = 0;
while (-1 != (n = zsIn.read(buffer))) {
    out.write(buffer, 0, n);
}
out.close();
zsIn.close();
]]></source>

        <p>Compressing a given file using the Zstandard format (you
        would certainly add exception handling and make sure all
        streams get closed properly):</p>
<source><![CDATA[
InputStream in = Files.newInputStream(Paths.get("archive.tar"));
OutputStream fout = Files.newOutputStream(Paths.get("archive.tar.zstd"));
BufferedOutputStream out = new BufferedOutputStream(fout);
ZstdCompressorOutputStream zOut = new ZstdCompressorOutputStream(out);
final byte[] buffer = new byte[buffersize];
int n = 0;
while (-1 != (n = in.read(buffer))) {
    zOut.write(buffer, 0, n);
}
zOut.close();
in.close();
]]></source>

      </subsection>
    </section>

    <section name="Extending Commons Compress">

        <p>
          Starting in release 1.13, it is now possible to add Compressor- and ArchiverStream implementations using the 
          Java's <a href="https://docs.oracle.com/javase/7/docs/api/java/util/ServiceLoader.html">ServiceLoader</a> 
          mechanism.
        </p>

    <subsection name="Extending Commons Compress Compressors">

        <p>
          To provide your own compressor, you must make available on the classpath a file called 
          <code>META-INF/services/org.apache.commons.compress.compressors.CompressorStreamProvider</code>.
        </p>
        <p>
          This file MUST contain one fully-qualified class name per line.
        </p>
        <p>
          For example:
        </p>
        <pre>org.apache.commons.compress.compressors.TestCompressorStreamProvider</pre>
        <p>
          This class MUST implement the Commons Compress interface 
          <a href="apidocs/org/apache/commons/compress/compressors/CompressorStreamProvider.html">org.apache.commons.compress.compressors.CompressorStreamProvider</a>.
        </p>
    </subsection>

    <subsection name="Extending Commons Compress Archivers">

        <p>
          To provide your own compressor, you must make available on the classpath a file called 
          <code>META-INF/services/org.apache.commons.compress.archivers.ArchiveStreamProvider</code>.
        </p>
        <p>
          This file MUST contain one fully-qualified class name per line.
        </p>
        <p>
          For example:
        </p>
        <pre>org.apache.commons.compress.archivers.TestArchiveStreamProvider</pre>
        <p>
          This class MUST implement the Commons Compress interface 
          <a href="apidocs/org/apache/commons/compress/archivers/ArchiveStreamProvider.html">org.apache.commons.compress.archivers.ArchiveStreamProvider</a>.
        </p>
    </subsection>

    </section>
  </body>
</document>
