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Class Inflater

java.lang.Object
java.util.zip.Inflater
All Implemented Interfaces:
AutoCloseable
public class Inflater extends Object implements AutoCloseable
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.

Unless otherwise noted, passing a null argument to a constructor or method in this class will cause a NullPointerException to be thrown.

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

To release the resources used by an Inflater, an application must close it by invoking its end() or close() method.

API Note:
This class implements AutoCloseable to facilitate its usage with try-with-resources statement. The close() method simply calls end().

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


// Encode a String into bytes
String inputString = "blahblahblah\u20AC\u20AC";
byte[] input = inputString.getBytes(StandardCharsets.UTF_8);

// Compress the bytes
ByteArrayOutputStream compressedBaos = new ByteArrayOutputStream();
try (Deflater compressor = new Deflater()) {
    compressor.setInput(input);
    // Let the compressor know that the complete input
    // has been made available
    compressor.finish();
    // Keep compressing the input till the compressor
    // is finished compressing
    while (!compressor.finished()) {
        // Use some reasonable size for the temporary buffer
        // based on the data being compressed
        byte[] tmpBuffer = new byte[100];
        int numCompressed = compressor.deflate(tmpBuffer);
        // Copy over the compressed bytes from the temporary
        // buffer into the final byte array
        compressedBaos.write(tmpBuffer, 0, numCompressed);
    }
}

// Decompress the bytes
ByteArrayOutputStream decompressedBaos = new ByteArrayOutputStream();
try (Inflater decompressor = new Inflater()) {
    byte[] compressed = compressedBaos.toByteArray();
    decompressor.setInput(compressed, 0, compressed.length);
    while (!decompressor.finished()) {
        // Use some reasonable size for the temporary buffer,
        // based on the data being decompressed; in this example,
        // we use a small buffer size
        byte[] tmpBuffer = new byte[100];
        int numDecompressed = 0;
        try {
            numDecompressed = decompressor.inflate(tmpBuffer);
        } catch (DataFormatException dfe) {
            // Handle the exception suitably, in this example
            // we just rethrow it
            throw new RuntimeException(dfe);
        }
        // Copy over the decompressed bytes from the temporary
        // buffer into the final byte array
        decompressedBaos.write(tmpBuffer, 0, numDecompressed);
    }
}
// Decode the bytes into a String
String outputString = decompressedBaos.toString(StandardCharsets.UTF_8);
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 close()
Closes and releases the resources held by this Inflater and discards any unprocessed input.
void end()
Closes and releases the resources held by this Inflater 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()
Deprecated.
Use getBytesRead() instead
int getTotalOut()
Deprecated.
Use getBytesWritten() instead
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 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:
11
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
Throws:
IllegalStateException - if the Inflater is closed
See Also:

setDictionary

public void setDictionary(byte[] dictionary)
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
Throws:
IllegalStateException - if the Inflater is closed
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
Throws:
IllegalStateException - if the Inflater is closed
Since:
11
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
IllegalStateException - if the Inflater is closed
See Also:

inflate

public int inflate(byte[] output) 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.

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
Returns:
the actual number of uncompressed bytes
Throws:
DataFormatException - if the compressed data format is invalid
IllegalStateException - if the Inflater is closed
See Also:

inflate

public int inflate(ByteBuffer output) 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.

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.

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
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
IllegalStateException - if the Inflater is closed
Since:
11
See Also:

getAdler

public int getAdler()
Returns the ADLER-32 value of the uncompressed data.
Returns:
the ADLER-32 value of the uncompressed data
Throws:
IllegalStateException - if the Inflater is closed

getTotalIn

@Deprecated(since="23") public int getTotalIn()
Deprecated.
Use getBytesRead() instead
Returns the total number of compressed bytes input so far.
Implementation Requirements:
This method returns the equivalent of (int) getBytesRead() and therefore cannot return the correct value when it is greater than Integer.MAX_VALUE.
Returns:
the total number of compressed bytes input so far
Throws:
IllegalStateException - if the Inflater is closed

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
Throws:
IllegalStateException - if the Inflater is closed
Since:
1.5

getTotalOut

@Deprecated(since="23") public int getTotalOut()
Deprecated.
Use getBytesWritten() instead
Returns the total number of uncompressed bytes output so far.
Implementation Requirements:
This method returns the equivalent of (int) getBytesWritten() and therefore cannot return the correct value when it is greater than Integer.MAX_VALUE.
Returns:
the total number of uncompressed bytes output so far
Throws:
IllegalStateException - if the Inflater is closed

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
Throws:
IllegalStateException - if the Inflater is closed
Since:
1.5

reset

public void reset()
Resets inflater so that a new set of input data can be processed.
Throws:
IllegalStateException - if the Inflater is closed

end

public void end()
Closes and releases the resources held by this Inflater and discards any unprocessed input.

If the Inflater is already closed then invoking this method has no effect.

Implementation Requirements:
Subclasses should override this method to clean up the resources acquired by the subclass.
See Also:

close

public void close()
Closes and releases the resources held by this Inflater and discards any unprocessed input.
Specified by:
close in interface AutoCloseable
Implementation Requirements:
This method calls the end() method.
Since:
25

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Documentation extracted from Debian's OpenJDK Development Kit package.
Licensed under the GNU General Public License, version 2, with the Classpath Exception.
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https://docs.oracle.com/en/java/javase/25/docs/api/java.base/java/util/zip/Inflater.html