code: protected void initializeFilter( InputStream filterInput, OutputStream filterOutput)
      {
      try
        {
        // Create Transformer object.
        Source transform = getTransform();
        if( transform == null)
          {
          throw new IllegalStateException( "No XSLT transform specified");
          }
        TransformerFactory factory = TransformerFactory.newInstance();
        factory.setErrorListener( this);
        
        transformer_ = factory.newTransformer( transform);
        transformer_.setErrorListener( this);
        if( transformParams_ != null)
          {
          for( String paramName : transformParams_.keySet())
            {
            transformer_.setParameter( paramName, transformParams_.get( paramName));
            }
          }
        
        transformSource_ = new StreamSource( filterInput);
        transformResult_ = new StreamResult( filterOutput);
        }
      catch( Exception e)
        {
        throw new RuntimeException( "Can't initialize filter", e);
        } 
      }
docs: Initializes the filter.