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Class Inflater

java.lang.Object

java.util.zip.Inflater

public class Inflater extends Object

This class provides support for general purpose decompression using the popular ZLIB compression library. The ZLIB compression library was initially developed as part of the PNG graphics standard and is not protected by patents. It is fully described in the specifications at the java.util.zip package description.

This class inflates sequences of ZLIB compressed bytes. The input byte sequence is provided in either byte array or byte buffer, via one of the setInput() methods. The output byte sequence is written to the output byte array or byte buffer passed to the inflate() methods.

The following code fragment demonstrates a trivial compression and decompression of a string using Deflater and Inflater.

 try {
     // Encode a String into bytes
     String inputString = "blahblahblahâ¬â¬";
     byte[] input = inputString.getBytes("UTF-8");

     // Compress the bytes
     byte[] output = new byte[100];
     Deflater compresser = new Deflater();
     compresser.setInput(input);
     compresser.finish();
     int compressedDataLength = compresser.deflate(output);

     // Decompress the bytes
     Inflater decompresser = new Inflater();
     decompresser.setInput(output, 0, compressedDataLength);
     byte[] result = new byte[100];
     int resultLength = decompresser.inflate(result);
     decompresser.end();

     // Decode the bytes into a String
     String outputString = new String(result, 0, resultLength, "UTF-8");
 } catch (java.io.UnsupportedEncodingException ex) {
     // handle
 } catch (java.util.zip.DataFormatException ex) {
     // handle
 }

API Note:

To release resources used by this Inflater, the end() method should be called explicitly. Subclasses are responsible for the cleanup of resources acquired by the subclass. Subclasses that override Object.finalize() in order to perform cleanup should be modified to use alternative cleanup mechanisms such as Cleaner and remove the overriding finalize method.

Since:

1.1

See Also:

Constructor Summary

Constructor	Description
`Inflater()`	Creates a new decompressor.
`Inflater(boolean nowrap)`	Creates a new decompressor.

Method Summary

Modifier and Type	Method	Description
`void`	`end()`	Closes the decompressor and discards any unprocessed input.
`boolean`	`finished()`	Returns true if the end of the compressed data stream has been reached.
`int`	`getAdler()`	Returns the ADLER-32 value of the uncompressed data.
`long`	`getBytesRead()`	Returns the total number of compressed bytes input so far.
`long`	`getBytesWritten()`	Returns the total number of uncompressed bytes output so far.
`int`	`getRemaining()`	Returns the total number of bytes remaining in the input buffer.
`int`	`getTotalIn()`	Returns the total number of compressed bytes input so far.
`int`	`getTotalOut()`	Returns the total number of uncompressed bytes output so far.
`int`	`inflate(byte[] output)`	Uncompresses bytes into specified buffer.
`int`	`inflate(byte[] output, int off, int len)`	Uncompresses bytes into specified buffer.
`int`	`inflate(ByteBuffer output)`	Uncompresses bytes into specified buffer.
`boolean`	`needsDictionary()`	Returns true if a preset dictionary is needed for decompression.
`boolean`	`needsInput()`	Returns true if no data remains in the input buffer.
`void`	`reset()`	Resets inflater so that a new set of input data can be processed.
`void`	`setDictionary(byte[] dictionary)`	Sets the preset dictionary to the given array of bytes.
`void`	`setDictionary(byte[] dictionary, int off, int len)`	Sets the preset dictionary to the given array of bytes.
`void`	`setDictionary(ByteBuffer dictionary)`	Sets the preset dictionary to the bytes in the given buffer.
`void`	`setInput(byte[] input)`	Sets input data for decompression.
`void`	`setInput(byte[] input, int off, int len)`	Sets input data for decompression.
`void`	`setInput(ByteBuffer input)`	Sets input data for decompression.

Methods declared in class java.lang.Object

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

Constructor Details

Inflater

public Inflater(boolean nowrap)

Creates a new decompressor. If the parameter 'nowrap' is true then the ZLIB header and checksum fields will not be used. This provides compatibility with the compression format used by both GZIP and PKZIP.

Note: When using the 'nowrap' option it is also necessary to provide an extra "dummy" byte as input. This is required by the ZLIB native library in order to support certain optimizations.

Parameters:: nowrap - if true then support GZIP compatible compression

Inflater

public Inflater()

Creates a new decompressor.

Method Details

setInput

public void setInput(byte[] input, int off, int len)

Sets input data for decompression.

One of the setInput() methods should be called whenever needsInput() returns true indicating that more input data is required.

Parameters:

input - the input data bytes

off - the start offset of the input data

len - the length of the input data

See Also:

setInput

public void setInput(byte[] input)

Sets input data for decompression.

One of the setInput() methods should be called whenever needsInput() returns true indicating that more input data is required.

Parameters:

input - the input data bytes

See Also:

setInput

public void setInput(ByteBuffer input)

Sets input data for decompression.

One of the setInput() methods should be called whenever needsInput() returns true indicating that more input data is required.

The given buffer's position will be advanced as inflate operations are performed, up to the buffer's limit. The input buffer may be modified (refilled) between inflate operations; doing so is equivalent to creating a new buffer and setting it with this method.

Modifying the input buffer's contents, position, or limit concurrently with an inflate operation will result in undefined behavior, which may include incorrect operation results or operation failure.

Parameters:

input - the input data bytes

Since:

See Also:

setDictionary

public void setDictionary(byte[] dictionary, int off, int len)

Sets the preset dictionary to the given array of bytes. Should be called when inflate() returns 0 and needsDictionary() returns true indicating that a preset dictionary is required. The method getAdler() can be used to get the Adler-32 value of the dictionary needed.

Parameters:

dictionary - the dictionary data bytes

off - the start offset of the data

len - the length of the data

See Also:

setDictionary

public void setDictionary(byte[] dictionary)

Parameters:

dictionary - the dictionary data bytes

See Also:

setDictionary

public void setDictionary(ByteBuffer dictionary)

Sets the preset dictionary to the bytes in the given buffer. Should be called when inflate() returns 0 and needsDictionary() returns true indicating that a preset dictionary is required. The method getAdler() can be used to get the Adler-32 value of the dictionary needed.

The bytes in given byte buffer will be fully consumed by this method. On return, its position will equal its limit.

Parameters:

dictionary - the dictionary data bytes

Since:

See Also:

getRemaining

public int getRemaining()

Returns the total number of bytes remaining in the input buffer. This can be used to find out what bytes still remain in the input buffer after decompression has finished.

Returns:: the total number of bytes remaining in the input buffer

needsInput

public boolean needsInput()

Returns true if no data remains in the input buffer. This can be used to determine if one of the setInput() methods should be called in order to provide more input.

Returns:: true if no data remains in the input buffer

needsDictionary

public boolean needsDictionary()

Returns true if a preset dictionary is needed for decompression.

Returns:

true if a preset dictionary is needed for decompression

See Also:

finished

public boolean finished()

Returns true if the end of the compressed data stream has been reached.

Returns:: true if the end of the compressed data stream has been reached

inflate

public int inflate(byte[] output, int off, int len) throws DataFormatException

Uncompresses bytes into specified buffer. Returns actual number of bytes uncompressed. A return value of 0 indicates that needsInput() or needsDictionary() should be called in order to determine if more input data or a preset dictionary is required. In the latter case, getAdler() can be used to get the Adler-32 value of the dictionary required.

If the setInput(ByteBuffer) method was called to provide a buffer for input, the input buffer's position will be advanced by the number of bytes consumed by this operation, even in the event that a DataFormatException is thrown.

The remaining byte count will be reduced by the number of consumed input bytes. If the setInput(ByteBuffer) method was called to provide a buffer for input, the input buffer's position will be advanced the number of consumed bytes.

These byte totals, as well as the total bytes read and the total bytes written values, will be updated even in the event that a DataFormatException is thrown to reflect the amount of data consumed and produced before the exception occurred.

Parameters:

output - the buffer for the uncompressed data

off - the start offset of the data

len - the maximum number of uncompressed bytes

Returns:

the actual number of uncompressed bytes

Throws:

DataFormatException - if the compressed data format is invalid

See Also:

inflate

public int inflate(byte[] output) throws DataFormatException

Parameters:

output - the buffer for the uncompressed data

Returns:

the actual number of uncompressed bytes

Throws:

DataFormatException - if the compressed data format is invalid

See Also:

inflate

public int inflate(ByteBuffer output) throws DataFormatException

On success, the position of the given output byte buffer will be advanced by as many bytes as were produced by the operation, which is equal to the number returned by this method. Note that the position of the output buffer will be advanced even in the event that a DataFormatException is thrown.

Parameters:

output - the buffer for the uncompressed data

Returns:

the actual number of uncompressed bytes

Throws:

DataFormatException - if the compressed data format is invalid

ReadOnlyBufferException - if the given output buffer is read-only

Since:

See Also:

getAdler

public int getAdler()

Returns the ADLER-32 value of the uncompressed data.

Returns:: the ADLER-32 value of the uncompressed data

getTotalIn

public int getTotalIn()

Returns the total number of compressed bytes input so far.

Since the number of bytes may be greater than Integer.MAX_VALUE, the getBytesRead() method is now the preferred means of obtaining this information.

Returns:: the total number of compressed bytes input so far

getBytesRead

public long getBytesRead()

Returns the total number of compressed bytes input so far.

Returns:: the total (non-negative) number of compressed bytes input so far
Since:: 1.5

getTotalOut

public int getTotalOut()

Returns the total number of uncompressed bytes output so far.

Since the number of bytes may be greater than Integer.MAX_VALUE, the getBytesWritten() method is now the preferred means of obtaining this information.

Returns:: the total number of uncompressed bytes output so far

getBytesWritten

public long getBytesWritten()

Returns the total number of uncompressed bytes output so far.

Returns:: the total (non-negative) number of uncompressed bytes output so far
Since:: 1.5

reset

public void reset()

Resets inflater so that a new set of input data can be processed.

end

public void end()

Closes the decompressor and discards any unprocessed input. This method should be called when the decompressor is no longer being used. Once this method is called, the behavior of the Inflater object is undefined.

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