Protege 3.4.8

edu.stanford.smi.protege.server.socket.deflate
Class CompressingOutputStream

java.lang.Object
  extended by java.io.OutputStream
      extended by edu.stanford.smi.protege.server.socket.deflate.CompressingOutputStream
All Implemented Interfaces:
Closeable, Flushable
Direct Known Subclasses:
HybridCompressingOutputStream

public class CompressingOutputStream
extends OutputStream

This code is based on the ideas presented in http://javatechniques.com/blog/compressing-data-sent-over-a-socket/ 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).

Author:
tredmond

Field Summary
protected  byte[] buffer
           
static int BUFFER_SIZE
           
static int COMPRESSION_PAD
           
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 java.io.OutputStream
close, write, write
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Field Detail

COMPRESSION_PAD

public static int COMPRESSION_PAD

BUFFER_SIZE

public static int BUFFER_SIZE

KB

public static int KB

os

protected OutputStream os

buffer

protected byte[] buffer

offset

protected int offset
Constructor Detail

CompressingOutputStream

public CompressingOutputStream(OutputStream os)
Method Detail

write

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

flush

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

logPacket

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

Protege 3.4.8

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