org.tukaani.xz
Class LZMA2InputStream

java.lang.Object
  extended by java.io.InputStream
      extended by org.tukaani.xz.LZMA2InputStream
All Implemented Interfaces:
Closeable

public class LZMA2InputStream
extends InputStream

Decompresses a raw LZMA2 stream (no XZ headers).


Field Summary
static int DICT_SIZE_MAX
          Largest dictionary size supported by this implementation.
static int DICT_SIZE_MIN
          Smallest valid LZMA2 dictionary size.
 
Constructor Summary
LZMA2InputStream(InputStream in, int dictSize)
          Creates a new input stream that decompresses raw LZMA2 data from in.
LZMA2InputStream(InputStream in, int dictSize, byte[] presetDict)
          Creates a new LZMA2 decompressor using a preset dictionary.
 
Method Summary
 int available()
          Returns the number of uncompressed bytes that can be read without blocking.
 void close()
          Closes the stream and calls in.close().
static int getMemoryUsage(int dictSize)
          Gets approximate decompressor memory requirements as kibibytes for the given dictionary size.
 int read()
          Decompresses the next byte from this input stream.
 int read(byte[] buf, int off, int len)
          Decompresses into an array of bytes.
 
Methods inherited from class java.io.InputStream
mark, markSupported, read, reset, skip
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Field Detail

DICT_SIZE_MIN

public static final int DICT_SIZE_MIN
Smallest valid LZMA2 dictionary size.

Very tiny dictionaries would be a performance problem, so the minimum is 4 KiB.

See Also:
Constant Field Values

DICT_SIZE_MAX

public static final int DICT_SIZE_MAX
Largest dictionary size supported by this implementation.

The LZMA2 algorithm allows dictionaries up to one byte less than 4 GiB. This implementation supports only 16 bytes less than 2 GiB for raw LZMA2 streams, and for .xz files the maximum is 1.5 GiB. This limitation is due to Java using signed 32-bit integers for array indexing. The limitation shouldn't matter much in practice since so huge dictionaries are not normally used.

See Also:
Constant Field Values
Constructor Detail

LZMA2InputStream

public LZMA2InputStream(InputStream in,
                        int dictSize)
Creates a new input stream that decompresses raw LZMA2 data from in.

The caller needs to know the dictionary size used when compressing; the dictionary size isn't stored as part of a raw LZMA2 stream.

Specifying a too small dictionary size will prevent decompressing the stream. Specifying a too big dictionary is waste of memory but decompression will work.

There is no need to specify a dictionary bigger than the uncompressed size of the data even if a bigger dictionary was used when compressing. If you know the uncompressed size of the data, this might allow saving some memory.

Parameters:
in - input stream from which LZMA2-compressed data is read
dictSize - LZMA2 dictionary size as bytes, must be in the range [DICT_SIZE_MIN, DICT_SIZE_MAX]

LZMA2InputStream

public LZMA2InputStream(InputStream in,
                        int dictSize,
                        byte[] presetDict)
Creates a new LZMA2 decompressor using a preset dictionary.

This is like LZMAInputStream(InputStream, int) except that the dictionary may be initialized using a preset dictionary. If a preset dictionary was used when compressing the data, the same preset dictionary must be provided when decompressing.

Parameters:
in - input stream from which LZMA2-compressed data is read
dictSize - LZMA2 dictionary size as bytes, must be in the range [DICT_SIZE_MIN, DICT_SIZE_MAX]
presetDict - preset dictionary or null to use no preset dictionary
Method Detail

getMemoryUsage

public static int getMemoryUsage(int dictSize)
Gets approximate decompressor memory requirements as kibibytes for the given dictionary size.

Parameters:
dictSize - LZMA2 dictionary size as bytes, must be in the range [DICT_SIZE_MIN, DICT_SIZE_MAX]
Returns:
approximate memory requirements as kibibytes (KiB)

read

public int read()
         throws IOException
Decompresses the next byte from this input stream.

Reading lots of data with read() from this input stream may be inefficient. Wrap it in java.io.BufferedInputStream if you need to read lots of data one byte at a time.

Specified by:
read in class InputStream
Returns:
the next decompressed byte, or -1 to indicate the end of the compressed stream
Throws:
CorruptedInputException
XZIOException - if the stream has been closed
EOFException - compressed input is truncated or corrupt
IOException - may be thrown by in

read

public int read(byte[] buf,
                int off,
                int len)
         throws IOException
Decompresses into an array of bytes.

If len is zero, no bytes are read and 0 is returned. Otherwise this will block until len bytes have been decompressed, the end of LZMA2 stream is reached, or an exception is thrown.

Overrides:
read in class InputStream
Parameters:
buf - target buffer for uncompressed data
off - start offset in buf
len - maximum number of uncompressed bytes to read
Returns:
number of bytes read, or -1 to indicate the end of the compressed stream
Throws:
CorruptedInputException
XZIOException - if the stream has been closed
EOFException - compressed input is truncated or corrupt
IOException - may be thrown by in

available

public int available()
              throws IOException
Returns the number of uncompressed bytes that can be read without blocking. The value is returned with an assumption that the compressed input data will be valid. If the compressed data is corrupt, CorruptedInputException may get thrown before the number of bytes claimed to be available have been read from this input stream.

In LZMAInputStream, the return value will be non-zero when the decompressor is in the middle of an LZMA2 chunk. The return value will then be the number of uncompressed bytes remaining from that chunk.

Overrides:
available in class InputStream
Returns:
the number of uncompressed bytes that can be read without blocking
Throws:
IOException

close

public void close()
           throws IOException
Closes the stream and calls in.close(). If the stream was already closed, this does nothing.

Specified by:
close in interface Closeable
Overrides:
close in class InputStream
Throws:
IOException - if thrown by in.close()