org.apache.commons.compress.compressors.lz77support

Class AbstractLZ77CompressorInputStream

java.lang.Object

java.io.InputStream

org.apache.commons.compress.compressors.CompressorInputStream

org.apache.commons.compress.compressors.lz77support.AbstractLZ77CompressorInputStream

All Implemented Interfaces:

java.io.Closeable, java.lang.AutoCloseable

Direct Known Subclasses:

BlockLZ4CompressorInputStream, SnappyCompressorInputStream

public abstract class AbstractLZ77CompressorInputStream
extends CompressorInputStream

Encapsulates code common to LZ77 decompressors.

Assumes the stream consists of blocks of literal data and back-references (called copies) in any order. Of course the first block must be a literal block for the scheme to work - unless the prefill method has been used to provide initial data that is never returned by read but only used for back-references.

Subclasses must override the three-arg read method as the no-arg version delegates to it and the default implementation delegates to the no-arg version, leading to infinite mutual recursion and a StackOverflowError otherwise.

The contract for subclasses' read implementation is:

• keep track of the current state of the stream. Is it inside a literal block or a back-reference or in-between blocks?
• Use readOneByte() to access the underlying stream directly.
• If a new literal block starts, use startLiteral(long) to tell this class about it and read the literal data using readLiteral(byte[], int, int) until it returns 0. hasMoreDataInBlock() will return false before the next call to readLiteral(byte[], int, int) would return 0.
• If a new back-reference starts, use startBackReference(int, long) to tell this class about it and read the literal data using readBackReference(byte[], int, int) until it returns 0. hasMoreDataInBlock() will return false before the next call to readBackReference(byte[], int, int) would return 0.
• If the end of the stream has been reached, return -1 as this class' methods will never do so themselves.

readOneByte() and readLiteral(byte[], int, int) update the counter for bytes read.

Since:

1.14

Constructor Summary

Constructors

Constructor and Description
AbstractLZ77CompressorInputStream(java.io.InputStream is, int windowSize) Creates a new LZ77 input stream.

Method Summary

Modifier and Type	Method and Description
int	available()
void	close()
int	getSize() Get the uncompressed size of the stream
void	prefill(byte[] data) Adds some initial data to fill the window with.
int	read()

Methods inherited from class org.apache.commons.compress.compressors.CompressorInputStream

getBytesRead, getCount

Methods inherited from class java.io.InputStream

mark, markSupported, read, read, reset, skip

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

AbstractLZ77CompressorInputStream

public AbstractLZ77CompressorInputStream(java.io.InputStream is,
                                         int windowSize)
                                  throws java.io.IOException

Creates a new LZ77 input stream.

Parameters:

is - An InputStream to read compressed data from

windowSize - Size of the window kept for back-references, must be bigger than the biggest offset expected.

Throws:

java.io.IOException - if reading fails

Method Detail

read

public int read()
         throws java.io.IOException

Specified by:

read in class java.io.InputStream

Throws:

java.io.IOException

close

public void close()
           throws java.io.IOException

Specified by:

close in interface java.io.Closeable

Specified by:

close in interface java.lang.AutoCloseable

Overrides:

close in class java.io.InputStream

Throws:

java.io.IOException

available

public int available()

Overrides:

available in class java.io.InputStream

getSize

public int getSize()

Get the uncompressed size of the stream

Returns:

the uncompressed size

prefill

public void prefill(byte[] data)

Adds some initial data to fill the window with.

This is used if the stream has been cut into blocks and back-references of one block may refer to data of the previous block(s). One such example is the LZ4 frame format using block dependency.

Parameters:

data - the data to fill the window with.

Throws:

java.lang.IllegalStateException - if the stream has already started to read data