Java. BarCode Ean-13 to String

I have a project, that draws a price tag, which has a barcode in it. To draw a barcode i use a JLabel with EAN-13 font set in. The input data, from which the price tag is generated, consists of two barcode attributes: the barcode number

080432402184 for example

and the encoded version, which is passed to the previosly mentioned JLabel

!h04324|PRQXTp for that barcode number

The problem is that i dont have access to the code, which generates the encoded version, and the algorithm that generates it has bugs. Because of that i want to write that thing from scrap, but having trouble finding the encoding algorithm.

Can someone point me to where i can find instructions on encoding it? Thanks.

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The Barcode4J problem. Trying to create a Graphics2D object and draw a barcode on it(cant really use a file out, because the barcode is only a part of the price tag).

Trying to do this using Java2DCanvasProvider:

EAN13Bean bean = new EAN13Bean();

    final int dpi = 150;

    //Configure the barcode generator
    bean.setModuleWidth(UnitConv.in2mm(13.3f / dpi)); //makes the narrow bar 
                                                     //width exactly one pixel
    bean.doQuietZone(true);

    bean.setHeight(chart.getBarcodeMainHeight()-10);
    bean.setFontSize(10f);

    BufferedImage bi = new BufferedImage(chart.getBarcodeMainWidth(), chart.getBarcodeMainHeight(), BufferedImage.TYPE_INT_RGB);
    Graphics2D graphics = bi.createGraphics();

    //graphics.fillRect(0, 0, chart.getBarcodeMainWidth(), chart.getBarcodeMainHeight());
    Java2DCanvasProvider canv = new Java2DCanvasProvider(graphics, 0);

    bean.generateBarcode(canv, priceTag.getBarCodeNumber());

    barCodeLabel.setIcon(new ImageIcon(bi));

but i recieve an inverted image block(i'm really new to Graphics2D).

Barcode4J has your back on this. It can also generate the images, so you can let go of the JLabel and the special font.