如何合并具有相同图层名称的多个 PDF 并为 output 获取更短的图层列表

Question

I'm using iText to merge several PDFs with layer. Each pdf file contains two layers: 'Cut' and 'Crease'.

Code:

public void testMergePdfMerger() throws Exception {

    String[] srcPdfs = new String[]{
            resourceFile("pdf/4901.pdf"),
            resourceFile("pdf/4902.pdf"),
            // more files here...

    };

    String destPdf = targetFile("MergerSimple.pdf");

    try (PdfDocument tgt = new PdfDocument(new PdfWriter(destPdf))) {
        PdfMerger merger = new PdfMerger(tgt);
        for (String srcPdf : srcPdfs) {
            try (PdfDocument src = new PdfDocument(new PdfReader(srcPdf))) {
                merger.merge(src, 1, src.getNumberOfPages());

            }
        }
    }
}

The target pdf contains the correct content. However, the layer list contains many layers with similar names.

Can I change some code so that the merged file only contains two layers: 'Cut' and 'Crease'?

With the following code, I can remove the layer name postfix.

        List<PdfLayer> layers = tgt.getCatalog().getOCProperties(false).getLayers();
        for(PdfLayer layer: layers) {
            String currentLayerName = layer.getPdfObject().get(PdfName.Name).toString();
            layer.setName(currentLayerName.replaceAll("_\\d+$", ""));
        }

But still not clear how to reuse the layer name from the first input pdf file.

Answer 1

You can set the smart mode on the PdfWriter to enable the reuse of resources (see https://api.itextpdf.com/iText7/java/7.1.14/com/itextpdf/kernel/pdf/PdfWriter.html#setSmartMode-boolean- )

try (PdfDocument tgt = new PdfDocument(new PdfWriter(destPdf).setSmartMode(true))) {
    [...]
}