Class Deflater

java.lang.Object

java.util.zip.Deflater

All Implemented Interfaces:: AutoCloseable

public class Deflater extends Object implements AutoCloseable

This class provides support for general purpose compression 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 method in this class will cause a NullPointerException to be thrown.

This class deflates sequences of bytes into ZLIB compressed data format. 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 deflate() methods.

To release the resources used by a Deflater, 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:

Field Summary

Modifier and Type	Field	Description
`static final int`	`BEST_COMPRESSION`	Compression level for best compression.
`static final int`	`BEST_SPEED`	Compression level for fastest compression.
`static final int`	`DEFAULT_COMPRESSION`	Default compression level.
`static final int`	`DEFAULT_STRATEGY`	Default compression strategy.
`static final int`	`DEFLATED`	Compression method for the deflate algorithm (the only one currently supported).
`static final int`	`FILTERED`	Compression strategy best used for data consisting mostly of small values with a somewhat random distribution.
`static final int`	`FULL_FLUSH`	Compression flush mode used to flush out all pending output and reset the deflater.
`static final int`	`HUFFMAN_ONLY`	Compression strategy for Huffman coding only.
`static final int`	`NO_COMPRESSION`	Compression level for no compression.
`static final int`	`NO_FLUSH`	Compression flush mode used to achieve best compression result.
`static final int`	`SYNC_FLUSH`	Compression flush mode used to flush out all pending output; may degrade compression for some compression algorithms.

Constructor Summary

Constructor	Description
`Deflater()`	Creates a new compressor with the default compression level.
`Deflater(int level)`	Creates a new compressor using the specified compression level.
`Deflater(int level, boolean nowrap)`	Creates a new compressor using the specified compression level.

Method Summary

Modifier and Type	Method	Description
`void`	`close()`	Closes and releases the resources held by this `Deflater` and discards any unprocessed input.
`int`	`deflate(byte[] output)`	Compresses the input data and fills specified buffer with compressed data.
`int`	`deflate(byte[] output, int off, int len)`	Compresses the input data and fills specified buffer with compressed data.
`int`	`deflate(byte[] output, int off, int len, int flush)`	Compresses the input data and fills the specified buffer with compressed data.
`int`	`deflate(ByteBuffer output)`	Compresses the input data and fills specified buffer with compressed data.
`int`	`deflate(ByteBuffer output, int flush)`	Compresses the input data and fills the specified buffer with compressed data.
`void`	`end()`	Closes and releases the resources held by this `Deflater` and discards any unprocessed input.
`void`	`finish()`	When called, indicates that compression should end with the current contents of the input buffer.
`boolean`	`finished()`	Returns true if the end of the compressed data output stream has been reached.
`int`	`getAdler()`	Returns the ADLER-32 value of the uncompressed data.
`long`	`getBytesRead()`	Returns the total number of uncompressed bytes input so far.
`long`	`getBytesWritten()`	Returns the total number of compressed bytes output so far.
`int`	`getTotalIn()`	Deprecated. Use `getBytesRead()` instead
`int`	`getTotalOut()`	Deprecated. Use `getBytesWritten()` instead
`boolean`	`needsInput()`	Returns true if no data remains in the input buffer.
`void`	`reset()`	Resets deflater so that a new set of input data can be processed.
`void`	`setDictionary(byte[] dictionary)`	Sets preset dictionary for compression.
`void`	`setDictionary(byte[] dictionary, int off, int len)`	Sets preset dictionary for compression.
`void`	`setDictionary(ByteBuffer dictionary)`	Sets preset dictionary for compression.
`void`	`setInput(byte[] input)`	Sets input data for compression.
`void`	`setInput(byte[] input, int off, int len)`	Sets input data for compression.
`void`	`setInput(ByteBuffer input)`	Sets input data for compression.
`void`	`setLevel(int level)`	Sets the compression level to the specified value.
`void`	`setStrategy(int strategy)`	Sets the compression strategy to the specified value.

Methods declared in class Object

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

Modifier and Type	Method	Description
`protected Object`	`clone()`	Creates and returns a copy of this object.
`boolean`	`equals(Object obj)`	Indicates whether some other object is "equal to" this one.
`protected void`	`finalize()`	Deprecated, for removal: This API element is subject to removal in a future version. Finalization is deprecated and subject to removal in a future release.
`final Class<?>`	`getClass()`	Returns the runtime class of this `Object`.
`int`	`hashCode()`	Returns a hash code value for this object.
`final void`	`notify()`	Wakes up a single thread that is waiting on this object's monitor.
`final void`	`notifyAll()`	Wakes up all threads that are waiting on this object's monitor.
`String`	`toString()`	Returns a string representation of the object.
`final void`	`wait()`	Causes the current thread to wait until it is awakened, typically by being notified or interrupted.
`final void`	`wait(long timeoutMillis)`	Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.
`final void`	`wait(long timeoutMillis, int nanos)`	Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.

Field Details

DEFLATED

public static final int DEFLATED

Compression method for the deflate algorithm (the only one currently supported).

See Also:

NO_COMPRESSION

public static final int NO_COMPRESSION

Compression level for no compression.

See Also:

BEST_SPEED

public static final int BEST_SPEED

Compression level for fastest compression.

See Also:

BEST_COMPRESSION

public static final int BEST_COMPRESSION

Compression level for best compression.

See Also:

DEFAULT_COMPRESSION

public static final int DEFAULT_COMPRESSION

Default compression level.

See Also:

FILTERED

public static final int FILTERED

Compression strategy best used for data consisting mostly of small values with a somewhat random distribution. Forces more Huffman coding and less string matching.

See Also:

HUFFMAN_ONLY

public static final int HUFFMAN_ONLY

Compression strategy for Huffman coding only.

See Also:

DEFAULT_STRATEGY

public static final int DEFAULT_STRATEGY

Default compression strategy.

See Also:

NO_FLUSH

public static final int NO_FLUSH

Compression flush mode used to achieve best compression result.

Since:

1.7

See Also:

SYNC_FLUSH

public static final int SYNC_FLUSH

Compression flush mode used to flush out all pending output; may degrade compression for some compression algorithms.

Since:

1.7

See Also:

FULL_FLUSH

public static final int FULL_FLUSH

Compression flush mode used to flush out all pending output and reset the deflater. Using this mode too often can seriously degrade compression.

Since:

1.7

See Also:

Constructor Details

Deflater

public Deflater(int level, boolean nowrap)

Creates a new compressor using the specified compression level. If 'nowrap' is true then the ZLIB header and checksum fields will not be used in order to support the compression format used in both GZIP and PKZIP.

Parameters:: level - the compression level (0-9); nowrap - if true then use GZIP compatible compression

Deflater

public Deflater(int level)

Creates a new compressor using the specified compression level. Compressed data will be generated in ZLIB format.

Parameters:: level - the compression level (0-9)

Deflater

public Deflater()

Creates a new compressor with the default compression level. Compressed data will be generated in ZLIB format.

Method Details

setInput

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

Sets input data for compression.

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 data

len - the length of the data

See Also:

setInput

public void setInput(byte[] input)

Sets input data for compression.

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 compression.

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 deflate operations are performed, up to the buffer's limit. The input buffer may be modified (refilled) between deflate 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 deflate 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 preset dictionary for compression. A preset dictionary is used when the history buffer can be predetermined. When the data is later uncompressed with Inflater.inflate(), Inflater.getAdler() can be called in order to get the Adler-32 value of the dictionary required for decompression.

Parameters:

dictionary - the dictionary data bytes

off - the start offset of the data

len - the length of the data

Throws:

IllegalStateException - if the Deflater is closed

See Also:

setDictionary

public void setDictionary(byte[] dictionary)

Parameters:

dictionary - the dictionary data bytes

Throws:

IllegalStateException - if the Deflater is closed

See Also:

setDictionary

public void setDictionary(ByteBuffer dictionary)

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 Deflater is closed

Since:

See Also:

setStrategy

public void setStrategy(int strategy)

Sets the compression strategy to the specified value.

If the compression strategy is changed, the next invocation of deflate will compress the input available so far with the old strategy (and may be flushed); the new strategy will take effect only after that invocation.

Parameters:: strategy - the new compression strategy
Throws:: IllegalArgumentException - if the compression strategy is invalid

setLevel

public void setLevel(int level)

Sets the compression level to the specified value.

If the compression level is changed, the next invocation of deflate will compress the input available so far with the old level (and may be flushed); the new level will take effect only after that invocation.

Parameters:: level - the new compression level (0-9)
Throws:: IllegalArgumentException - if the compression level is invalid

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 the input data buffer is empty and setInput() should be called in order to provide more input

finish

public void finish()

When called, indicates that compression should end with the current contents of the input buffer.

finished

public boolean finished()

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

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

deflate

public int deflate(byte[] output, int off, int len)

Compresses the input data and fills specified buffer with compressed data. Returns actual number of bytes of compressed data. A return value of 0 indicates that needsInput should be called in order to determine if more input data is required.

This method uses NO_FLUSH as its compression flush mode. An invocation of this method of the form deflater.deflate(b, off, len) yields the same result as the invocation of deflater.deflate(b, off, len, Deflater.NO_FLUSH).

Parameters:: output - the buffer for the compressed data; off - the start offset of the data; len - the maximum number of bytes of compressed data
Returns:: the actual number of bytes of compressed data written to the output buffer
Throws:: IllegalStateException - if the Deflater is closed

deflate

public int deflate(byte[] output)

This method uses NO_FLUSH as its compression flush mode. An invocation of this method of the form deflater.deflate(b) yields the same result as the invocation of deflater.deflate(b, 0, b.length, Deflater.NO_FLUSH).

Parameters:: output - the buffer for the compressed data
Returns:: the actual number of bytes of compressed data written to the output buffer
Throws:: IllegalStateException - if the Deflater is closed

deflate

public int deflate(ByteBuffer output)

This method uses NO_FLUSH as its compression flush mode. An invocation of this method of the form deflater.deflate(output) yields the same result as the invocation of deflater.deflate(output, Deflater.NO_FLUSH).

Parameters:: output - the buffer for the compressed data
Returns:: the actual number of bytes of compressed data written to the output buffer
Throws:: ReadOnlyBufferException - if the given output buffer is read-only; IllegalStateException - if the Deflater is closed
Since:: 11

deflate

public int deflate(byte[] output, int off, int len, int flush)

Compresses the input data and fills the specified buffer with compressed data. Returns actual number of bytes of data compressed.

Compression flush mode is one of the following three modes:

NO_FLUSH: allows the deflater to decide how much data to accumulate, before producing output, in order to achieve the best compression (should be used in normal use scenario). A return value of 0 in this flush mode indicates that needsInput() should be called in order to determine if more input data is required.
SYNC_FLUSH: all pending output in the deflater is flushed, to the specified output buffer, so that an inflater that works on compressed data can get all input data available so far (In particular the needsInput() returns true after this invocation if enough output space is provided). Flushing with SYNC_FLUSH may degrade compression for some compression algorithms and so it should be used only when necessary.
FULL_FLUSH: all pending output is flushed out as with SYNC_FLUSH. The compression state is reset so that the inflater that works on the compressed output data can restart from this point if previous compressed data has been damaged or if random access is desired. Using FULL_FLUSH too often can seriously degrade compression.

In the case of FULL_FLUSH or SYNC_FLUSH, if the return value is len, the space available in output buffer b, this method should be invoked again with the same flush parameter and more output space. Make sure that len is greater than 6 to avoid flush marker (5 bytes) being repeatedly output to the output buffer every time this method is invoked.

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.

Parameters:: output - the buffer for the compressed data; off - the start offset of the data; len - the maximum number of bytes of compressed data; flush - the compression flush mode
Returns:: the actual number of bytes of compressed data written to the output buffer
Throws:: IllegalArgumentException - if the flush mode is invalid; IllegalStateException - if the Deflater is closed
Since:: 1.7

deflate

public int deflate(ByteBuffer output, int flush)

Compresses the input data and fills the specified buffer with compressed data. Returns actual number of bytes of data compressed.

Compression flush mode is one of the following three modes:

NO_FLUSH: allows the deflater to decide how much data to accumulate, before producing output, in order to achieve the best compression (should be used in normal use scenario). A return value of 0 in this flush mode indicates that needsInput() should be called in order to determine if more input data is required.
SYNC_FLUSH: all pending output in the deflater is flushed, to the specified output buffer, so that an inflater that works on compressed data can get all input data available so far (In particular the needsInput() returns true after this invocation if enough output space is provided). Flushing with SYNC_FLUSH may degrade compression for some compression algorithms and so it should be used only when necessary.
FULL_FLUSH: all pending output is flushed out as with SYNC_FLUSH. The compression state is reset so that the inflater that works on the compressed output data can restart from this point if previous compressed data has been damaged or if random access is desired. Using FULL_FLUSH too often can seriously degrade compression.

In the case of FULL_FLUSH or SYNC_FLUSH, if the return value is equal to the remaining space of the buffer, this method should be invoked again with the same flush parameter and more output space. Make sure that the buffer has at least 6 bytes of remaining space to avoid the flush marker (5 bytes) being repeatedly output to the output buffer every time this method is invoked.

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.

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.

Parameters:: output - the buffer for the compressed data; flush - the compression flush mode
Returns:: the actual number of bytes of compressed data written to the output buffer
Throws:: IllegalArgumentException - if the flush mode is invalid; ReadOnlyBufferException - if the given output buffer is read-only; IllegalStateException - if the Deflater is closed
Since:: 11

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 Deflater is closed

getTotalIn

@Deprecated(since="23") public int getTotalIn()

Deprecated.

Use getBytesRead() instead

Returns the total number of uncompressed 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 uncompressed bytes input so far
Throws:: IllegalStateException - if the Deflater is closed

getBytesRead

public long getBytesRead()

Returns the total number of uncompressed bytes input so far.

Returns:: the total (non-negative) number of uncompressed bytes input so far
Throws:: IllegalStateException - if the Deflater is closed
Since:: 1.5

getTotalOut

@Deprecated(since="23") public int getTotalOut()

Deprecated.

Use getBytesWritten() instead

Returns the total number of compressed 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 compressed bytes output so far
Throws:: IllegalStateException - if the Deflater is closed

getBytesWritten

public long getBytesWritten()

Returns the total number of compressed bytes output so far.

Returns:: the total (non-negative) number of compressed bytes output so far
Throws:: IllegalStateException - if the Deflater is closed
Since:: 1.5

reset

public void reset()

Resets deflater so that a new set of input data can be processed. Keeps current compression level and strategy settings.

Throws:: IllegalStateException - if the Deflater is closed

end

public void end()

Closes and releases the resources held by this Deflater and discards any unprocessed input.

If the Deflater 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 Deflater 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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