Protege 3.4.8

Class CompressingOutputStream

  extended by
      extended by edu.stanford.smi.protege.server.socket.deflate.CompressingOutputStream
All Implemented Interfaces:
Closeable, Flushable
Direct Known Subclasses:

public class CompressingOutputStream
extends OutputStream

This code is based on the ideas presented in by Philip Isenhour. I am very grateful for the approach that he presented. The key idea is to avoid using the GZip and the Zip streams and to use the Deflater and Inflater methods directly. In addition, Philip Isenhour essentially defines a packet type that has a header indicating the size and compressed size of the packet contents. I took these two key ideas and wrote the following code by scratch without reference to Philip Isenhour's documents. I think that some version of Philip Isenhour's ideas should find their way into the core java libraries because otherwise people will continue struggling with this problem.

I have tried several other approaches to a compressing input and compressing output stream. The first approach was to base the input and output streams on the GZip input and output stream. There are web pages on the internet that suggest that calling the GZipOutputStream's finish() method during the flush() will work. I had trouble with this approach when a write occurs on the stream after the flush() (which calls finish()). I would get exceptions indicating that the GZip Output stream was finished and therefore unwriteable.

I then tried to use the ZIPInput/OutputStreams. I would flush data by creating a ZipEntry and writing it out. This approach actually worked very well. But it had a mysterious bug where some data was either not fully written out or not read. In the rmi context things would hang. This bug was relatively rare and only happened on certain machines. I never found out what the problem was.

The beauty of Philip Isenhour's approach is that the developer can completely control how data is flushed and fully written out. The developer can also ensure that on the read method all the data is fully read. So there should not be any more rmi hangs. The only issue is whether the deflate/inflate logic is correct. This is pretty thoroughly tested in our server-client testing (though there are *always* bugs hidden somewhere).


Field Summary
protected  byte[] buffer
static int BUFFER_SIZE
static int KB
protected  int offset
protected  OutputStream os
Constructor Summary
CompressingOutputStream(OutputStream os)
Method Summary
 void flush()
protected  void logPacket(byte[] compressedBuffer, int compressedSize)
 void write(int b)
Methods inherited from class
close, write, write
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail


public static int COMPRESSION_PAD


public static int BUFFER_SIZE


public static int KB


protected OutputStream os


protected byte[] buffer


protected int offset
Constructor Detail


public CompressingOutputStream(OutputStream os)
Method Detail


public void write(int b)
           throws IOException
Specified by:
write in class OutputStream


public void flush()
           throws IOException
Specified by:
flush in interface Flushable
flush in class OutputStream


protected void logPacket(byte[] compressedBuffer,
                         int compressedSize)

Protege 3.4.8

Submit a bug report or feature request
Protégé is a trademark of Stanford University.
Copyright (c) 1998-2012 Stanford University.