Size of GZIPOutputStream

[Tom Henricksen]

Is there any way to tell the size of GZIPOutputStream? We are trying to figure out how much the compression is helping us. I see nothing in the javadoc and I can understand this would be difficult if not impossible. We are trying to use a compression filter and see if we are adding any value.

Thanks,
Tom

[Paul Clapham]

When in the java.io package, use the Decorator pattern. Here's a CountingOutputStream that lets you count the bytes written to an output stream:

public class CountingOutputStream extends OutputStream {
 
  OutputStream stream;
  int bytes = 0;
 
  public CountingOutputStream(OutputStream stream) {
    this.stream = stream;
  }
 
  public void close() throws IOException {
    stream.close();
  }
  public void flush() throws IOException {
    stream.flush();
  }
  public void write(byte[] b) throws IOException {
    stream.write(b);
    bytes += b.length;
  }
  public void write(byte[] b, int offset, int len) throws IOException {
    stream.write(b, offset, len);
    bytes += len;
  }
  public void write(int b) throws IOException {
    stream.write(b);
    bytes += 1;
  }
  public int getBytesWritten() {
    return bytes;
  }
 
}

You would use one of these to see how many bytes the GZipOutputStream wrote to the output, and another to see how many bytes you wrote to the GZipOutputStream:

CountingOutputStream coso = new CountingOutputStream(response.getOutputStream());
CountingOutputStream cosi = new CountingOutputStream(new GZipOutputStream(coso));
 
... code goes here
 
int bytesOut = coso.getBytesWritten();
int bytesIn = cosi.getBytesWritten();

[Tom Henricksen]

Thanks Paul that looks like it will do the trick!

[Jim Yingst]

Often decorators in java.io (e.g. PrintStream and BufferedOutputStream) are expressed using FilterOutputStream or other FilterXXX classes. These give you the standard functionality of wrapping another stream, and forwarding methods calls like flush() and close(). And write(byte[] arr) just calls write(arr, 0, arr.length). So you just add the new functionality:

public class CountingOutputStream extends FilterOutputStream {
    
    private int count;
 
    public CountingOutputStream(OutputStream out) { super(out); }
 
    public void write(int b) throws IOException { 
        super.write(b);   
        count++;
    }
 
    public void write(byte b[], int off, int len) throws IOException {
        super.write(b, off, len); 
        count += len;
    }
 
    public int getCount() { return count; }
}

[ May 11, 2007: Message edited by: Jim Yingst ]