iText 7.0.2 Java合并PdfDocument列表为单PDF的问题求助

Let's break down why your previous attempts failed and fix this step by step:

• First attempt error: You tried copying pages from PdfDocument instances that were still attached to a PdfWriter (they were in an active "writing" state). iText blocks copying indirect objects from a document that’s still being written to.
• Second attempt error: Every PdfPage is tightly bound to its parent PdfDocument—you can’t directly move or add a page from one document to another without proper copying logic.
• Third attempt issue: When you re-read the PDFs without first finalizing the filled forms, the form data wasn’t persisted correctly, leading to lost content.

The Core Fix: Store Completed PDF Byte Arrays, Not Open PdfDocument Instances #

The root problem is you’re storing open, write-bound PdfDocument objects. Instead, you need to fully finalize each filled PDF (close the document, capture its byte content) and store those byte arrays. Then use PdfMerger to combine them properly.

Step 1: Modify Form Filling to Store Byte Arrays

ArrayList<byte[]> pdfBytesList = new ArrayList<>();
while (rs.next()) {
    URL fullPath = context.getResource("/formulare/kontrollbogen.pdf");
    ByteArrayOutputStream bos = new ByteArrayOutputStream();
    PdfWriter writer = new PdfWriter(bos);
    PdfReader reader = new PdfReader(fullPath.getFile());
    PdfDocument doc = new PdfDocument(reader, writer);
    
    // Fill your form fields
    PdfAcroForm form = PdfAcroForm.getAcroForm(doc, true);
    String firma = rs.getString("firma");
    if (firma != null && !firma.isEmpty()) {
        form.getField("firma").setValue(firma);
    }
    // Add other form field population logic here...
    
    // Critical: Close the document to finalize all content
    doc.close();
    // Store the completed PDF as a byte array
    pdfBytesList.add(bos.toByteArray());
}

Step 2: Merge Byte Arrays with PdfMerger

ByteArrayOutputStream mergedBos = new ByteArrayOutputStream();
PdfWriter mergedWriter = new PdfWriter(mergedBos);
PdfDocument mergedDoc = new PdfDocument(mergedWriter);
PdfMerger merger = new PdfMerger(mergedDoc);

for (byte[] pdfBytes : pdfBytesList) {
    // Create a reader from the stored byte array
    PdfReader reader = new PdfReader(new ByteArrayInputStream(pdfBytes));
    PdfDocument tempDoc = new PdfDocument(reader);
    // Merge all pages from the temp document into the merged one
    merger.merge(tempDoc, 1, tempDoc.getNumberOfPages());
    tempDoc.close();
}

// Finalize the merged document
mergedDoc.close();

// mergedBos now contains your complete merged PDF with all form data intact

Why This Works #

• Closing each filled PdfDocument ensures all form data and PDF structure is properly written to the ByteArrayOutputStream.
• Storing byte arrays means you’re working with complete, finalized PDFs—not open, stateful document instances.
• PdfMerger handles page copying and indirect object management correctly, avoiding the errors you ran into earlier.

内容的提问来源于stack exchange，提问作者Dennis Weinmann