itext7 pdf merger

itext7AddCover.groovy

import com.sap.gateway.ip.core.customdev.util.Message as CpiMsg
import com.itextpdf.kernel.pdf.PdfDocument
import com.itextpdf.kernel.pdf.PdfReader
import com.itextpdf.kernel.pdf.PdfWriter
import com.itextpdf.kernel.utils.PdfMerger

import java.util.zip.ZipInputStream

CpiMsg addCover(CpiMsg msg) {
    ZipInputStream zis = new ZipInputStream(getClass().getResourceAsStream("/lib/hero.jar"))    // zipped new cover
    zis.nextEntry
    PdfDocument cover = new PdfDocument(new PdfReader(zis))
    
    ByteArrayOutputStream dest = new ByteArrayOutputStream()
    PdfDocument pdfDoc = new PdfDocument(new PdfWriter(dest))
    PdfDocument input = new PdfDocument(new PdfReader(msg.getBody(InputStream)))

    PdfMerger merger = new PdfMerger(pdfDoc)
    merger.merge(cover, 1, 1)
    merger.merge(input, 1, input.getNumberOfPages())
    cover.close()
    input.close()
    merger.close()
    dest.close()

    msg.headers."content-type" = "application/pdf"
    msg.setBody(dest.toByteArray())
    
    
    return msg
}