org.tukaani.xz
Class XZOutputStream

java.lang.Object
  extended by java.io.OutputStream
      extended by org.tukaani.xz.FinishableOutputStream
          extended by org.tukaani.xz.XZOutputStream
All Implemented Interfaces:
java.io.Closeable, java.io.Flushable

public class XZOutputStream
extends FinishableOutputStream

Compresses into the .xz file format.

Examples

Getting an output stream to compress with LZMA2 using the default settings and the default integrity check type (CRC64):

 FileOutputStream outfile = new FileOutputStream("foo.xz");
 XZOutputStream outxz = new XZOutputStream(outfile, new LZMA2Options());
 

Using the preset level 8 for LZMA2 (the default is 6) and SHA-256 instead of CRC64 for integrity checking:

 XZOutputStream outxz = new XZOutputStream(outfile, new LZMA2Options(8),
                                           XZ.CHECK_SHA256);
 

Using the x86 BCJ filter together with LZMA2 to compress x86 executables and printing the memory usage information before creating the XZOutputStream:

 X86Options x86 = new X86Options();
 LZMA2Options lzma2 = new LZMA2Options();
 FilterOptions[] options = { x86, lzma2 };
 System.out.println("Encoder memory usage: "
                    + FilterOptions.getEncoderMemoryUsage(options)
                    + " KiB");
 System.out.println("Decoder memory usage: "
                    + FilterOptions.getDecoderMemoryUsage(options)
                    + " KiB");
 XZOutputStream outxz = new XZOutputStream(outfile, options);
 


Constructor Summary
XZOutputStream(java.io.OutputStream out, FilterOptions filterOptions)
          Creates a new XZ compressor using one filter and CRC64 as the integrity check.
XZOutputStream(java.io.OutputStream out, FilterOptions[] filterOptions)
          Creates a new XZ compressor using 1-4 filters and CRC64 as the integrity check.
XZOutputStream(java.io.OutputStream out, FilterOptions[] filterOptions, int checkType)
          Creates a new XZ compressor using 1-4 filters and the specified integrity check type.
XZOutputStream(java.io.OutputStream out, FilterOptions filterOptions, int checkType)
          Creates a new XZ compressor using one filter and the specified integrity check type.
 
Method Summary
 void close()
          Finishes compression and closes the underlying stream.
 void endBlock()
          Finishes the current XZ Block (but not the whole XZ Stream).
 void finish()
          Finishes compression without closing the underlying stream.
 void flush()
          Flushes the encoder and calls out.flush().
 void updateFilters(FilterOptions filterOptions)
          Updates the filter chain with a single filter.
 void updateFilters(FilterOptions[] filterOptions)
          Updates the filter chain with 1-4 filters.
 void write(byte[] buf, int off, int len)
          Writes an array of bytes to be compressed.
 void write(int b)
          Writes one byte to be compressed.
 
Methods inherited from class java.io.OutputStream
write
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Constructor Detail

XZOutputStream

public XZOutputStream(java.io.OutputStream out,
                      FilterOptions filterOptions)
               throws java.io.IOException
Creates a new XZ compressor using one filter and CRC64 as the integrity check. This constructor is equivalent to passing a single-member FilterOptions array to XZOutputStream(OutputStream, FilterOptions[]).

Parameters:
out - output stream to which the compressed data will be written
filterOptions - filter options to use
Throws:
UnsupportedOptionsException - invalid filter chain
java.io.IOException - may be thrown from out

XZOutputStream

public XZOutputStream(java.io.OutputStream out,
                      FilterOptions filterOptions,
                      int checkType)
               throws java.io.IOException
Creates a new XZ compressor using one filter and the specified integrity check type. This constructor is equivalent to passing a single-member FilterOptions array to XZOutputStream(OutputStream, FilterOptions[], int).

Parameters:
out - output stream to which the compressed data will be written
filterOptions - filter options to use
checkType - type of the integrity check, for example XZ.CHECK_CRC32
Throws:
UnsupportedOptionsException - invalid filter chain
java.io.IOException - may be thrown from out

XZOutputStream

public XZOutputStream(java.io.OutputStream out,
                      FilterOptions[] filterOptions)
               throws java.io.IOException
Creates a new XZ compressor using 1-4 filters and CRC64 as the integrity check. This constructor is equivalent XZOutputStream(out, filterOptions, XZ.CHECK_CRC64).

Parameters:
out - output stream to which the compressed data will be written
filterOptions - array of filter options to use
Throws:
UnsupportedOptionsException - invalid filter chain
java.io.IOException - may be thrown from out

XZOutputStream

public XZOutputStream(java.io.OutputStream out,
                      FilterOptions[] filterOptions,
                      int checkType)
               throws java.io.IOException
Creates a new XZ compressor using 1-4 filters and the specified integrity check type.

Parameters:
out - output stream to which the compressed data will be written
filterOptions - array of filter options to use
checkType - type of the integrity check, for example XZ.CHECK_CRC32
Throws:
UnsupportedOptionsException - invalid filter chain
java.io.IOException - may be thrown from out
Method Detail

updateFilters

public void updateFilters(FilterOptions filterOptions)
                   throws XZIOException
Updates the filter chain with a single filter. This is equivalent to passing a single-member FilterOptions array to updateFilters(FilterOptions[]).

Parameters:
filterOptions - new filter to use
Throws:
UnsupportedOptionsException - unsupported filter chain, or trying to change the filter chain in the middle of a Block
XZIOException

updateFilters

public void updateFilters(FilterOptions[] filterOptions)
                   throws XZIOException
Updates the filter chain with 1-4 filters.

Currently this cannot be used to update e.g. LZMA2 options in the middle of a XZ Block. Use endBlock() to finish the current XZ Block before calling this function. The new filter chain will then be used for the next XZ Block.

Parameters:
filterOptions - new filter chain to use
Throws:
UnsupportedOptionsException - unsupported filter chain, or trying to change the filter chain in the middle of a Block
XZIOException

write

public void write(int b)
           throws java.io.IOException
Writes one byte to be compressed.

Specified by:
write in class java.io.OutputStream
Throws:
XZIOException - XZ Stream has grown too big
XZIOException - finish() or close() was already called
java.io.IOException - may be thrown by the underlying output stream

write

public void write(byte[] buf,
                  int off,
                  int len)
           throws java.io.IOException
Writes an array of bytes to be compressed. The compressors tend to do internal buffering and thus the written data won't be readable from the compressed output immediately. Use flush() to force everything written so far to be written to the underlaying output stream, but be aware that flushing reduces compression ratio.

Overrides:
write in class java.io.OutputStream
Parameters:
buf - buffer of bytes to be written
off - start offset in buf
len - number of bytes to write
Throws:
XZIOException - XZ Stream has grown too big: total file size about 8 EiB or the Index field exceeds 16 GiB; you shouldn't reach these sizes in practice
XZIOException - finish() or close() was already called and len > 0
java.io.IOException - may be thrown by the underlying output stream

endBlock

public void endBlock()
              throws java.io.IOException
Finishes the current XZ Block (but not the whole XZ Stream). This doesn't flush the stream so it's possible that not all data will be decompressible from the output stream when this function returns. Call also flush() if flushing is wanted in addition to finishing the current XZ Block.

If there is no unfinished Block open, this function will do nothing. (No empty XZ Block will be created.)

This function can be useful, for example, to create random-accessible .xz files.

Starting a new XZ Block means that the encoder state is reset. Doing this very often will increase the size of the compressed file a lot (more than plain flush() would do).

Throws:
XZIOException - XZ Stream has grown too big
XZIOException - stream finished or closed
java.io.IOException - may be thrown by the underlying output stream

flush

public void flush()
           throws java.io.IOException
Flushes the encoder and calls out.flush(). All buffered pending data will then be decompressible from the output stream.

Calling this function very often may increase the compressed file size a lot. The filter chain options may affect the size increase too. For example, with LZMA2 the HC4 match finder has smaller penalty with flushing than BT4.

Some filters don't support flushing. If the filter chain has such a filter, flush() will call endBlock() before flushing.

Specified by:
flush in interface java.io.Flushable
Overrides:
flush in class java.io.OutputStream
Throws:
XZIOException - XZ Stream has grown too big
XZIOException - stream finished or closed
java.io.IOException - may be thrown by the underlying output stream

finish

public void finish()
            throws java.io.IOException
Finishes compression without closing the underlying stream. No more data can be written to this stream after finishing (calling write with an empty buffer is OK).

Repeated calls to finish() do nothing unless an exception was thrown by this stream earlier. In that case the same exception is thrown again.

After finishing, the stream may be closed normally with close(). If the stream will be closed anyway, there usually is no need to call finish() separately.

Overrides:
finish in class FinishableOutputStream
Throws:
XZIOException - XZ Stream has grown too big
java.io.IOException - may be thrown by the underlying output stream

close

public void close()
           throws java.io.IOException
Finishes compression and closes the underlying stream. The underlying stream out is closed even if finishing fails. If both finishing and closing fail, the exception thrown by finish() is thrown and the exception from the failed out.close() is lost.

Specified by:
close in interface java.io.Closeable
Overrides:
close in class java.io.OutputStream
Throws:
XZIOException - XZ Stream has grown too big
java.io.IOException - may be thrown by the underlying output stream