org.tentackle.util
Class CompressedOutputStream

java.lang.Object
  java.io.OutputStream
      java.io.FilterOutputStream
          org.tentackle.util.CompressedOutputStream

All Implemented Interfaces:

Closeable, Flushable

public class CompressedOutputStream
extends FilterOutputStream

Stream to write compressed data to the underlying output stream.

Replacement for GZIPOutputStream and ZipOutputStream of java.util.zip capable for communication link streams like tcp-sockets. The standard classes are only file-capable (relying on EOF-detection). In comlinks, however, there are several packets instead of a single file. Hence, the stream must be blocked, i.e. the (varying) blocksize must become part of the protocol to allow the corresponding input stream to detect the end of the packets. Furthermore, we optimize to compress only packets larger than a certain size. All smaller packets will be transferred uncompressed. For the packet size we use the first two bytes in the packet (short), while MSBit signals whether the packet is compressed or not. Because of this, the maximum buffer size is limited to 32K - 1.

Field Summary

static int

MAX_BUFFER_SIZE The maximum compression buffer size.

Fields inherited from class java.io.FilterOutputStream

out

Constructor Summary

CompressedOutputStream(OutputStream out)
Creates a compressed output stream with maximum allowed buffersize (32K-1) and a default minCompressSize of 64.

CompressedOutputStream(OutputStream out, int bufSize, int minCompressSize)
Creates a compressed output stream.

Method Summary

void	close() Overridden to print stats only
void	flush() Flushes this output stream and forces any buffered output bytes to be written out to the stream.
boolean	isClosed()
void	write(byte[] b, int off, int len) Writes len bytes from the specified byte array starting at offset off to this output stream.
void	write(int b) Writes the specified byte to this output stream.

Methods inherited from class java.io.FilterOutputStream

write

Methods inherited from class java.lang.Object

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

Field Detail

MAX_BUFFER_SIZE

public static final int MAX_BUFFER_SIZE

The maximum compression buffer size. The larger the buffer, the better the compression.

See Also:

Constant Field Values

Constructor Detail

CompressedOutputStream

public CompressedOutputStream(OutputStream out,
                              int bufSize,
                              int minCompressSize)

Creates a compressed output stream.

Parameters:

out - the underlying output stream (e.g. from a socket)

bufSize - the buffer size for compression. Packets larger than bufSize are split.

minCompressSize - the minimum compressed packet size. Smaller packets pass the stream uncompressed.

CompressedOutputStream

public CompressedOutputStream(OutputStream out)

Creates a compressed output stream with maximum allowed buffersize (32K-1) and a default minCompressSize of 64.

Parameters:

out - the underlying output stream

Method Detail

write

public void write(int b)
           throws IOException

Writes the specified byte to this output stream.

Overrides:

write in class FilterOutputStream

Parameters:

b - the byte.

Throws:

IOException - if an I/O error occurs.

write

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

Writes len bytes from the specified byte array starting at offset off to this output stream.

Packets larger than the buffer size will be split and written to the underlying output stream as separate packets.

Overrides:

write in class FilterOutputStream

Parameters:

b - the data.

off - the start offset in the data.

len - the number of bytes to write.

Throws:

IOException - if an I/O error occurs.

See Also:

FilterOutputStream.write(int)

flush

public void flush()
           throws IOException

Flushes this output stream and forces any buffered output bytes to be written out to the stream.

Specified by:

flush in interface Flushable

Overrides:

flush in class FilterOutputStream

Throws:

IOException - if an I/O error occurs.

See Also:

FilterOutputStream.out

close

public void close()
           throws IOException

Overridden to print stats only

Specified by:

close in interface Closeable

Overrides:

close in class FilterOutputStream

Throws:

IOException - if an I/O error occurs.

See Also:

FilterOutputStream.flush(), FilterOutputStream.out

isClosed

public boolean isClosed()

Returns:

true if closed