org.aredis.io

Class CompressibleByteArrayOutputStream

java.lang.Object

java.io.OutputStream

org.aredis.io.CompressibleByteArrayOutputStream

All Implemented Interfaces:

Closeable, Flushable, AutoCloseable

public class CompressibleByteArrayOutputStream
extends OutputStream

An OutputStream that compresses the data once the size crosses a certain threshold. The setCompressionEnabled can be used to turn off compressions for sections that are not part of the data and should not be compressed. When compressionEnabled is flipped from false to true a new compression session is started and the data size is counted from that point and when it exceeds the threshold the stream is reset to that point, a GZIPOutputStream is started and the data in session is written to the GZIPOutputStream. compressionEnabled is false for commands and keys. It is turned on by the DataHandler if it supports compression.

When gzip compression is on the stream does not store the original data. To avoid compressing data that is already compressed by gzip or other means a compression ratio check is made after every 1024 bytes. If the compression ratio is above the abandonCompressionRatio then the compression is abandoned. This is done by closing the GZIPOutputStream resetting the stream back to the start of the compression session, writing back the original data by uncompressing the data written and continuing with future writes without compression.

Author:

Suresh

Field Summary

Fields

Modifier and Type	Field and Description
static int	DEFAULT_COMPRESSION_THRESHOLD Default Compression Threshold.

Constructor Summary

Constructors

Constructor and Description
CompressibleByteArrayOutputStream() Creates a new CompressibleByteArrayOutputStream with the default compression threshold of 1024 bytes.
CompressibleByteArrayOutputStream(int pcompressionThreshold) Creates a new CompressibleByteArrayOutputStream.
CompressibleByteArrayOutputStream(int size, int pcompressionThreshold) Creates a new CompressibleByteArrayOutputStream.

Method Summary

Methods

Modifier and Type	Method and Description
boolean	clearCompressionInfo()
void	close()
double	getAbandonCompressionRatio() Gets the abandon compression ratio.
byte[]	getBuf() Gets the underlying buffer.
String	getCompressionInfo() Returns the current compression info as a String.
int	getCompressionThreshold() Gets the compression threshold.
int	getCount() Low level method to get the count of the data in the buffer.
int	getCountAtSessionStart() Low level method to get the count at the start of the current compression session.
PrintStream	getPrintStream(String charSet) Gets a printStream that writes to this Stream corresponding to a given Charset.
boolean	isAbandonCompressionEnabled() Checks if abandon compression is enabled.
boolean	isCompressed() Checks if compression is currently in effect.
boolean	isCompressionEnabled() Checks if compression is enabled.
void	reset() Resets the stream by clearing any existing data.
void	setAbandonCompressionEnabled(boolean pabandonCompressionEnabled) Sets if abandon compression should be enabled.
void	setAbandonCompressionRatio(double ratio) Sets the abandon compression ratio.
void	setCompressionEnabled(boolean pcompressionEnabled) Sets if compression is enabled.
void	setCompressionThreshold(int pcompressionThreshold) Sets the compression threshold.
void	setCount(int pcount) Low level method to set the count in the buffer.
void	write(byte[] b, int off, int len)
void	write(int b)
void	writeTo(OutputStream op) Writes the data in the Stream to an OutputStream

Methods inherited from class java.io.OutputStream

flush, write

Methods inherited from class java.lang.Object

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

Field Detail

DEFAULT_COMPRESSION_THRESHOLD

public static final int DEFAULT_COMPRESSION_THRESHOLD

Default Compression Threshold.

See Also:

Constant Field Values

Constructor Detail

CompressibleByteArrayOutputStream

public CompressibleByteArrayOutputStream(int pcompressionThreshold)

Creates a new CompressibleByteArrayOutputStream.

Parameters:

pcompressionThreshold - Compression Threshold in bytes

CompressibleByteArrayOutputStream

public CompressibleByteArrayOutputStream(int size,
                                 int pcompressionThreshold)

Creates a new CompressibleByteArrayOutputStream.

Parameters:

size - Initial buffer capacity

pcompressionThreshold - Compression Threshold in bytes

CompressibleByteArrayOutputStream

public CompressibleByteArrayOutputStream()

Creates a new CompressibleByteArrayOutputStream with the default compression threshold of 1024 bytes.

Method Detail

reset

public void reset()

Resets the stream by clearing any existing data. The compressionEnabled flag is unchanged.

getPrintStream

public PrintStream getPrintStream(String charSet)

Gets a printStream that writes to this Stream corresponding to a given Charset. The returned PrintStream is a sub-class of PrintStream that ignores closing of the stream. The same PrintStream is returned for the Same charSet for calls to getPrintStream on a given CompressionbleByteArrayOutputStream.

Parameters:

charSet - CharSet to use

Returns:

PrintStream that writes to this stream

write

public void write(byte[] b,
         int off,
         int len)

Overrides:

write in class OutputStream

write

public void write(int b)

Specified by:

write in class OutputStream

close

public void close()
           throws IOException

Specified by:

close in interface Closeable

Specified by:

close in interface AutoCloseable

Overrides:

close in class OutputStream

Throws:

IOException

writeTo

public void writeTo(OutputStream op)
             throws IOException

Writes the data in the Stream to an OutputStream

Parameters:

op - OutputStream to write the data to

Throws:

IOException - In case of an error during write

IllegalStateException - if compression is currently in effect on the stream

isCompressed

public boolean isCompressed()

Checks if compression is currently in effect. It might return false even if compressionEnabled is set but the data size is less than the compressionThreshold. It will also return false if the compression has been abandoned.

Returns:

true if compression is happening on the stream, false otherwise

getCount

public int getCount()

Low level method to get the count of the data in the buffer.

Returns:

Count

setCount

public void setCount(int pcount)

Low level method to set the count in the buffer.

Parameters:

pcount - New count

Throws:

IllegalStateException - if compression is currently in effect on the stream

getBuf

public byte[] getBuf()

Gets the underlying buffer.

Returns:

buffer used to store the data

getCompressionThreshold

public int getCompressionThreshold()

Gets the compression threshold.

Returns:

CompressionThreshold

setCompressionThreshold

public void setCompressionThreshold(int pcompressionThreshold)

Sets the compression threshold.

Parameters:

pcompressionThreshold - New Compression Threshold

isCompressionEnabled

public boolean isCompressionEnabled()

Checks if compression is enabled.

Returns:

true if compression is enabled

getCompressionInfo

public String getCompressionInfo()

Returns the current compression info as a String. Returns info on the data sizes before and after the compression. Also returns info regarding abandoning compression. Returns null if no compression was done. This should be called after the current compression session has been ended by calling setCompressionEnabled(false).

Returns:

Compression Info

clearCompressionInfo

public boolean clearCompressionInfo()

setCompressionEnabled

public void setCompressionEnabled(boolean pcompressionEnabled)

Sets if compression is enabled. If compression was previously disabled then a new compression session is started.

Parameters:

pcompressionEnabled - whether compression should be enabled

isAbandonCompressionEnabled

public boolean isAbandonCompressionEnabled()

Checks if abandon compression is enabled.

Returns:

true if abandon compression is enabled. False otherwise

setAbandonCompressionEnabled

public void setAbandonCompressionEnabled(boolean pabandonCompressionEnabled)

Sets if abandon compression should be enabled. This flag is automatically set if compression is re-enabled by calling setCompressionEnabled(true).

Parameters:

pabandonCompressionEnabled - true if abandon compression should be enabled, false otherwise.

getCountAtSessionStart

public int getCountAtSessionStart()

Low level method to get the count at the start of the current compression session.

Returns:

count value when compression was last enabled on this stream

getAbandonCompressionRatio

public double getAbandonCompressionRatio()

Gets the abandon compression ratio. If the compression ratio goes above this the compression is abandoned. The default is 0.7.

Returns:

Abandon Compression Ratio

setAbandonCompressionRatio

public void setAbandonCompressionRatio(double ratio)

Sets the abandon compression ratio. Only 2 decimal places are considered.

Parameters:

ratio - New Abandon Compression ratio