code: public static Iterator<ImageWriter> getImageWritersByFormatName(String formatName) {
  		if (formatName == null) {
  			throw new IllegalArgumentException("formatName == null!");
  		}
  		Iterator iter;
  		// Ensure category is present
  		try {
  			iter = theRegistry.getServiceProviders(ImageWriterSpi.class, new ContainsFilter(writerFormatNamesMethod, formatName), true);
  		} catch (IllegalArgumentException e) {
  			return new HashSet().iterator();
  		}
  		return new ImageWriterIterator(iter);
  	}
docs: Returns an <code>Iterator</code> containing all currently registered <code>ImageWriter</code>s that
  claim to be able to encode the named format.
  
  @param formatName
  a <code>String</code> containing the informal name of a format (<i>e.g.</i>, "jpeg" or
  "tiff".
  
  @return an <code>Iterator</code> containing <code>ImageWriter</code>s.
  
  @exception IllegalArgumentException
  if <code>formatName</code> is <code>null</code>.
  
  @see javax.imageio.spi.ImageWriterSpi#getFormatNames