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| java.lang.Object | |
| ↳ | java.util.zip.Deflater |
This class compresses data using the DEFLATE algorithm (see specification).
It is usually more convenient to use DeflaterOutputStream.
To compress an in-memory byte[] to another in-memory byte[] manually:
byte[] originalBytes = ...
Deflater deflater = new Deflater();
deflater.setInput(originalBytes);
deflater.finish();
ByteArrayOutputStream baos = new ByteArrayOutputStream();
byte[] buf = new byte[8192];
while (!deflater.finished()) {
int byteCount = deflater.deflate(buf);
baos.write(buf, 0, byteCount);
}
deflater.end();
byte[] compressedBytes = baos.toByteArray();
In situations where you don't have all the input in one array (or have so much
input that you want to feed it to the deflater in chunks), it's possible to call
setInput repeatedly, but you're much better off using
DeflaterOutputStream to handle all this for you. DeflaterOutputStream also helps
minimize memory requirements — the sample code above is very expensive.
Compression levels
A compression level must be DEFAULT_COMPRESSION to compromise between speed and
compression (currently equivalent to level 6), or between 0 (NO_COMPRESSION, where
the input is simply copied) and 9 (BEST_COMPRESSION). Level 1 (BEST_SPEED)
performs some compression, but with minimal speed overhead.
| Constants | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| int | BEST_COMPRESSION | This compression level gives the best compression, but takes the most time. | |||||||||
| int | BEST_SPEED | This compression level gives minimal compression,
but takes the least time (of any level that actually performs compression;
see NO_COMPRESSION). |
|||||||||
| int | DEFAULT_COMPRESSION | The default compression level. | |||||||||
| int | DEFAULT_STRATEGY | The default compression strategy. | |||||||||
| int | DEFLATED | The default compression method. | |||||||||
| int | FILTERED | A compression strategy. | |||||||||
| int | FULL_FLUSH | Flush buffers so recipients can immediately decode the data sent thus far. | |||||||||
| int | HUFFMAN_ONLY | A compression strategy. | |||||||||
| int | NO_COMPRESSION | This compression level does no compression. | |||||||||
| int | NO_FLUSH | Use buffering for best compression. | |||||||||
| int | SYNC_FLUSH | Flush buffers so recipients can immediately decode the data sent thus far. | |||||||||
| Public Constructors | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
Constructs a new
Deflater instance using the
default compression level. | |||||||||||
Constructs a new
Deflater instance with the
given compression level. | |||||||||||
Constructs a new
Deflater instance with the
given compression level. | |||||||||||
| Public Methods | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
Deflates data (previously passed to
setInput) into a specific
region within the supplied buffer, optionally flushing the input buffer. | |||||||||||
Deflates data (previously passed to
setInput) into a specific
region within the supplied buffer. | |||||||||||
Deflates the data (previously passed to
setInput) into the
supplied buffer. | |||||||||||
Frees all resources held onto by this deflating algorithm.
| |||||||||||
Indicates to the
Deflater that all uncompressed input has been provided
to it. | |||||||||||
Returns the
Adler32 checksum of the uncompressed data read so far. | |||||||||||
Returns the total number of bytes read by the
Deflater. | |||||||||||
Returns a the total number of bytes written by this
Deflater. | |||||||||||
Returns the total number of bytes of input read by this
Deflater. | |||||||||||
Returns the total number of bytes written to the output buffer by this
Deflater. | |||||||||||
Returns true if
setInput must be called before deflation can continue. | |||||||||||
Resets the
Deflater to accept new input without affecting any
previous compression strategy or level settings. | |||||||||||
Sets the dictionary to be used for compression by this
Deflater. | |||||||||||
Sets the dictionary to be used for compression by this
Deflater. | |||||||||||
Sets the input buffer the
Deflater will use to extract uncompressed bytes
for later compression. | |||||||||||
Sets the input buffer the
Deflater will use to extract uncompressed bytes
for later compression. | |||||||||||
Sets the given compression level
to be used when compressing data.
| |||||||||||
Sets the compression strategy to be used.
| |||||||||||
| Protected Methods | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
Invoked when the garbage collector has detected that this instance is no longer reachable.
| |||||||||||
|
[Expand]
Inherited Methods | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
From class
java.lang.Object
| |||||||||||
This compression level gives the best compression, but takes the most time.
This compression level gives minimal compression,
but takes the least time (of any level that actually performs compression;
see NO_COMPRESSION).
The default compression level. This is a trade-off between speed and compression, currently equivalent to level 6.
The default compression strategy.
The default compression method.
A compression strategy.
Flush buffers so recipients can immediately decode the data sent thus far. The compression state is also reset to permit random access and recovery for clients who have discarded or damaged their own copy. This mode may degrade compression.
A compression strategy.
This compression level does no compression.
It is even faster than BEST_SPEED.
Use buffering for best compression.
Flush buffers so recipients can immediately decode the data sent thus far. This mode may degrade compression.
Constructs a new Deflater instance using the
default compression level.
The compression strategy can be specified with setStrategy(int). A
header is added to the output by default; use Deflater(int, boolean) if you need to omit the header.
Constructs a new Deflater instance with the
given compression level.
The compression strategy can be specified with setStrategy(int).
A header is added to the output by default; use
Deflater(int, boolean) if you need to omit the header.
Constructs a new Deflater instance with the
given compression level.
If noHeader is true, no ZLIB header is added to the
output. In a zip file, every entry (compressed file) comes with such a
header. The strategy can be specified using setStrategy(int).
Deflates data (previously passed to setInput) into a specific
region within the supplied buffer, optionally flushing the input buffer.
| flush | one of NO_FLUSH, SYNC_FLUSH or FULL_FLUSH. |
|---|
buf. If this
equals byteCount, the number of bytes of input to be flushed
may have exceeded the output buffer's capacity. In this case,
finishing a flush will require the output buffer to be drained
and additional calls to deflate(byte[]) to be made.| IllegalArgumentException | if flush is invalid. |
|---|
Deflates data (previously passed to setInput) into a specific
region within the supplied buffer.
buf.
Deflates the data (previously passed to setInput) into the
supplied buffer.
buf.
Frees all resources held onto by this deflating algorithm. Any unused
input or output is discarded. This method should be called explicitly in
order to free native resources as soon as possible. After end() is
called, other methods will typically throw IllegalStateException.
Indicates to the Deflater that all uncompressed input has been provided
to it.
Returns the Adler32 checksum of the uncompressed data read so far.
Returns the total number of bytes read by the Deflater. This
method is the same as getTotalIn() except that it returns a
long value instead of an integer.
Returns a the total number of bytes written by this Deflater. This
method is the same as getTotalOut except it returns a
long value instead of an integer.
Returns the total number of bytes of input read by this Deflater. This
method is limited to 32 bits; use getBytesRead() instead.
Returns the total number of bytes written to the output buffer by this Deflater. The method is limited to 32 bits; use getBytesWritten() instead.
Resets the Deflater to accept new input without affecting any
previous compression strategy or level settings. This
operation must be called after finished() returns
true if the Deflater is to be reused.
Sets the dictionary to be used for compression by this Deflater.
This method can only be called if this Deflater supports the writing
of ZLIB headers. This is the default, but can be overridden
using Deflater(int, boolean).
Sets the dictionary to be used for compression by this Deflater.
This method can only be called if this Deflater supports the writing
of ZLIB headers. This is the default, but can be overridden
using Deflater(int, boolean).
Sets the input buffer the Deflater will use to extract uncompressed bytes
for later compression.
Sets the input buffer the Deflater will use to extract uncompressed bytes
for later compression.
Sets the given compression level
to be used when compressing data. This value must be set
prior to calling setInput.
| IllegalArgumentException | If the compression level is invalid. |
|---|
Sets the compression strategy to be used. The strategy must be one of
FILTERED, HUFFMAN_ONLY or DEFAULT_STRATEGY. This value must be set prior
to calling setInput.
| IllegalArgumentException | If the strategy specified is not one of FILTERED, HUFFMAN_ONLY or DEFAULT_STRATEGY. |
|---|
Invoked when the garbage collector has detected that this instance is no longer reachable. The default implementation does nothing, but this method can be overridden to free resources.
Note that objects that override finalize are significantly more expensive than
objects that don't. Finalizers may be run a long time after the object is no longer
reachable, depending on memory pressure, so it's a bad idea to rely on them for cleanup.
Note also that finalizers are run on a single VM-wide finalizer thread,
so doing blocking work in a finalizer is a bad idea. A finalizer is usually only necessary
for a class that has a native peer and needs to call a native method to destroy that peer.
Even then, it's better to provide an explicit close method (and implement
Closeable), and insist that callers manually dispose of instances. This
works well for something like files, but less well for something like a BigInteger
where typical calling code would have to deal with lots of temporaries. Unfortunately,
code that creates lots of temporaries is the worst kind of code from the point of view of
the single finalizer thread.
If you must use finalizers, consider at least providing your own
ReferenceQueue and having your own thread process that queue.
Unlike constructors, finalizers are not automatically chained. You are responsible for
calling super.finalize() yourself.
Uncaught exceptions thrown by finalizers are ignored and do not terminate the finalizer thread. See Effective Java Item 7, "Avoid finalizers" for more.