org.tukaani.xz

Class XZInputStream

java.lang.Object

java.io.InputStream

org.tukaani.xz.XZInputStream

All Implemented Interfaces:

Closeable, AutoCloseable

public class XZInputStream
extends InputStream

Decompresses a .xz file in streamed mode (no seeking).

Use this to decompress regular standalone .xz files. This reads from its input stream until the end of the input or until an error occurs. This supports decompressing concatenated .xz files.

Typical use cases

Getting an input stream to decompress a .xz file:

 InputStream infile = new FileInputStream("foo.xz");
 XZInputStream inxz = new XZInputStream(infile);
 

It's important to keep in mind that decompressor memory usage depends on the settings used to compress the file. The worst-case memory usage of XZInputStream is currently 1.5 GiB. Still, very few files will require more than about 65 MiB because that's how much decompressing a file created with the highest preset level will need, and only a few people use settings other than the predefined presets.

It is possible to specify a memory usage limit for XZInputStream. If decompression requires more memory than the specified limit, MemoryLimitException will be thrown when reading from the stream. For example, the following sets the memory usage limit to 100 MiB:

 InputStream infile = new FileInputStream("foo.xz");
 XZInputStream inxz = new XZInputStream(infile, 100 * 1024);
 

When uncompressed size is known beforehand

If you are decompressing complete files and your application knows exactly how much uncompressed data there should be, it is good to try reading one more byte by calling read() and checking that it returns -1. This way the decompressor will parse the file footers and verify the integrity checks, giving the caller more confidence that the uncompressed data is valid. (This advice seems to apply to java.util.zip.GZIPInputStream too.)

See Also:

SingleXZInputStream

Constructor Summary

Constructors

Constructor and Description
XZInputStream(InputStream in) Creates a new XZ decompressor without a memory usage limit.
XZInputStream(InputStream in, ArrayCache arrayCache) Creates a new XZ decompressor without a memory usage limit.
XZInputStream(InputStream in, int memoryLimit) Creates a new XZ decompressor with an optional memory usage limit.
XZInputStream(InputStream in, int memoryLimit, ArrayCache arrayCache) Creates a new XZ decompressor with an optional memory usage limit.
XZInputStream(InputStream in, int memoryLimit, boolean verifyCheck) Creates a new XZ decompressor with an optional memory usage limit and ability to disable verification of integrity checks.
XZInputStream(InputStream in, int memoryLimit, boolean verifyCheck, ArrayCache arrayCache) Creates a new XZ decompressor with an optional memory usage limit and ability to disable verification of integrity checks.

Method Summary

Methods

Modifier and Type	Method and Description
int	available() Returns the number of uncompressed bytes that can be read without blocking.
void	close() Closes the stream and calls in.close().
void	close(boolean closeInput) Closes the stream and optionally calls in.close().
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

Constructor Detail

XZInputStream

public XZInputStream(InputStream in)
              throws IOException

Creates a new XZ decompressor without a memory usage limit.

This constructor reads and parses the XZ Stream Header (12 bytes) from in. The header of the first Block is not read until read is called.

Parameters:

in - input stream from which XZ-compressed data is read

Throws:

XZFormatException - input is not in the XZ format

CorruptedInputException - XZ header CRC32 doesn't match

UnsupportedOptionsException - XZ header is valid but specifies options not supported by this implementation

EOFException - less than 12 bytes of input was available from in

IOException - may be thrown by in

XZInputStream

public XZInputStream(InputStream in,
             ArrayCache arrayCache)
              throws IOException

Creates a new XZ decompressor without a memory usage limit.

This is identical to XZInputStream(InputStream) except that this takes also the arrayCache argument.

Parameters:

in - input stream from which XZ-compressed data is read

arrayCache - cache to be used for allocating large arrays

Throws:

XZFormatException - input is not in the XZ format

CorruptedInputException - XZ header CRC32 doesn't match

UnsupportedOptionsException - XZ header is valid but specifies options not supported by this implementation

EOFException - less than 12 bytes of input was available from in

IOException - may be thrown by in

Since:

1.7

XZInputStream

public XZInputStream(InputStream in,
             int memoryLimit)
              throws IOException

Creates a new XZ decompressor with an optional memory usage limit.

This is identical to XZInputStream(InputStream) except that this takes also the memoryLimit argument.

Parameters:

in - input stream from which XZ-compressed data is read

memoryLimit - memory usage limit in kibibytes (KiB) or -1 to impose no memory usage limit

Throws:

XZFormatException - input is not in the XZ format

CorruptedInputException - XZ header CRC32 doesn't match

UnsupportedOptionsException - XZ header is valid but specifies options not supported by this implementation

EOFException - less than 12 bytes of input was available from in

IOException - may be thrown by in

XZInputStream

public XZInputStream(InputStream in,
             int memoryLimit,
             ArrayCache arrayCache)
              throws IOException

Creates a new XZ decompressor with an optional memory usage limit.

This is identical to XZInputStream(InputStream) except that this takes also the memoryLimit and arrayCache arguments.

Parameters:

in - input stream from which XZ-compressed data is read

memoryLimit - memory usage limit in kibibytes (KiB) or -1 to impose no memory usage limit

arrayCache - cache to be used for allocating large arrays

Throws:

XZFormatException - input is not in the XZ format

CorruptedInputException - XZ header CRC32 doesn't match

UnsupportedOptionsException - XZ header is valid but specifies options not supported by this implementation

EOFException - less than 12 bytes of input was available from in

IOException - may be thrown by in

Since:

1.7

XZInputStream

public XZInputStream(InputStream in,
             int memoryLimit,
             boolean verifyCheck)
              throws IOException

Creates a new XZ decompressor with an optional memory usage limit and ability to disable verification of integrity checks.

This is identical to XZInputStream(InputStream,int) except that this takes also the verifyCheck argument.

Note that integrity check verification should almost never be disabled. Possible reasons to disable integrity check verification:

• Trying to recover data from a corrupt .xz file.
• Speeding up decompression. This matters mostly with SHA-256 or with files that have compressed extremely well. It's recommended that integrity checking isn't disabled for performance reasons unless the file integrity is verified externally in some other way.

verifyCheck only affects the integrity check of the actual compressed data. The CRC32 fields in the headers are always verified.

Parameters:

in - input stream from which XZ-compressed data is read

memoryLimit - memory usage limit in kibibytes (KiB) or -1 to impose no memory usage limit

verifyCheck - if true, the integrity checks will be verified; this should almost never be set to false

Throws:

XZFormatException - input is not in the XZ format

CorruptedInputException - XZ header CRC32 doesn't match

UnsupportedOptionsException - XZ header is valid but specifies options not supported by this implementation

EOFException - less than 12 bytes of input was available from in

IOException - may be thrown by in

Since:

1.6

XZInputStream

public XZInputStream(InputStream in,
             int memoryLimit,
             boolean verifyCheck,
             ArrayCache arrayCache)
              throws IOException

Creates a new XZ decompressor with an optional memory usage limit and ability to disable verification of integrity checks.

This is identical to XZInputStream(InputStream,int,boolean) except that this takes also the arrayCache argument.

Parameters:

in - input stream from which XZ-compressed data is read

memoryLimit - memory usage limit in kibibytes (KiB) or -1 to impose no memory usage limit

verifyCheck - if true, the integrity checks will be verified; this should almost never be set to false

arrayCache - cache to be used for allocating large arrays

Throws:

XZFormatException - input is not in the XZ format

CorruptedInputException - XZ header CRC32 doesn't match

UnsupportedOptionsException - XZ header is valid but specifies options not supported by this implementation

EOFException - less than 12 bytes of input was available from in

IOException - may be thrown by in

Since:

1.7

Method Detail

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 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

UnsupportedOptionsException

MemoryLimitException

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 try to decompress len bytes of uncompressed data. Less than len bytes may be read only in the following situations:

• The end of the compressed data was reached successfully.
• An error is detected after at least one but less len bytes have already been successfully decompressed. The next call with non-zero len will immediately throw the pending exception.
• 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

UnsupportedOptionsException

MemoryLimitException

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.

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.

This is equivalent to close(true).

Specified by:

close in interface Closeable

Specified by:

close in interface AutoCloseable

Overrides:

close in class InputStream

Throws:

IOException - if thrown by in.close()

close

public void close(boolean closeInput)
           throws IOException

Closes the stream and optionally calls in.close(). If the stream was already closed, this does nothing. If close(false) has been called, a further call of close(true) does nothing (it doesn't call in.close()).

If you don't want to close the underlying InputStream, there is usually no need to worry about closing this stream either; it's fine to do nothing and let the garbage collector handle it. However, if you are using ArrayCache, close(false) can be useful to put the allocated arrays back to the cache without closing the underlying InputStream.

Note that if you successfully reach the end of the stream (read returns -1), the arrays are automatically put back to the cache by that read call. In this situation close(false) is redundant (but harmless).

Throws:

IOException - if thrown by in.close()

Since:

1.7