itext7-自动调整图像大小

Question

I use iText (Version 7.1.1) to convert html to pdf using HtmlConverter (html2pdf version 2.0.1) :

public static ByteArrayOutputStream htmlToPDFStream(String htmlBody)
        throws DocumentException, IOException {
ConverterProperties props = new ConverterProperties();

FontProvider fp = new DefaultFontProvider(true, false, false);
for (String font : FONTS) {
    FontProgram fontProgram = FontProgramFactory.createFont(font);
    fp.addFont(fontProgram);
}

props.setFontProvider(fp);

com.itextpdf.kernel.pdf.PdfWriter writer = new com.itextpdf.kernel.pdf.PdfWriter(outputStream);
PdfDocument pdf = new PdfDocument(writer);
Document document = new Document(pdf);

List<IElement> elements = HtmlConverter.convertToElements(new ByteArrayInputStream(htmlBody.getBytes(StandardCharsets.UTF_8)), props);
for (IElement element : elements) {
    document.add((IBlockElement)element);
}
document.close();
return  outputStream;
}

It works good if the HTML string has small images (smaller than default page size A4). But if I have an image bigger than default page width, the result will be cropped image in pdf.

Is there any way to tell iText to make auto resizing if the image is bigger than default pdf page size to be fit?

Answer 1

Images in layout have autoscale property which should result in desired behavior. You would need to define a custom ITagWorker to actually add this property to the produced image elements.

You would also have to define a custom ITagWorkerFactory to use new ITagWorker for images.

The code is very simple, you just have to tie everything together carefully:

class CustomImageWorker extends ImgTagWorker {
    public CustomImageWorker(IElementNode element, ProcessorContext context) {
        super(element, context);
    }

    @Override
    public IPropertyContainer getElementResult() {
        return ((Image)super.getElementResult()).setAutoScale(true);
    }
}

ITagWorkerFactory customFactory = new DefaultTagWorkerFactory() {
    @Override
    public ITagWorker getCustomTagWorker(IElementNode tag, ProcessorContext context) {
        if (TagConstants.IMG.equals(tag.name())) {
            return new CustomImageWorker(tag, context);
        } else {
            return null;
        }
    }
};

After that, just set your tag factory to the props: props.setTagWorkerFactory(customFactory);

Another solution at the CSS level would be to specify different image widths and heights depending on the media device settings, such as device width and height. See @media CSS rule documentation.

UPD If you don't have any width or height CSS properties defined for images, you can compare their sizes to page sizes directly, but keep in mind px to pt conversion rate. Example:

@Override
public IPropertyContainer getElementResult() {
    Image result = ((Image)super.getElementResult());
    if (!processed) {
        float imageWidth = result.getImageScaledWidth();
        float pageMargin = 36 * 2;
        float maxWidth = PageSize.A4.getWidth() - pageMargin;
        float maxHeight = PageSize.A4.getHeight() - pageMargin;
        if (imageWidth * 0.75 > maxWidth) {
            result.scaleToFit(maxWidth / 0.75f, maxHeight / 0.75f);
        }
        processed = true;
    }
    return result;
}