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

    java.lang.Object
      java.io.OutputStream
          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)

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