How to generate a link inside a footnote with Apache POI?

I am able to create footnotes, and I'm able to make links, but when I try to make a link inside a footnote Word refuses to open the resulting document.

Here's a minimal example that reproduces the problem:

import java.io.File;
import java.io.FileOutputStream;

import org.apache.poi.xwpf.usermodel.XWPFAbstractFootnoteEndnote;
import org.apache.poi.xwpf.usermodel.XWPFDocument;
import org.apache.poi.xwpf.usermodel.XWPFHyperlinkRun;
import org.apache.poi.xwpf.usermodel.XWPFParagraph;
import org.apache.poi.xwpf.usermodel.XWPFRelation;
import org.apache.poi.xwpf.usermodel.XWPFRun;
import org.openxmlformats.schemas.wordprocessingml.x2006.main.CTHyperlink;
import org.openxmlformats.schemas.wordprocessingml.x2006.main.CTR;

public class Test {
  public static void main(String[] argv) throws Exception {
    XWPFDocument document = new XWPFDocument();
    XWPFParagraph para = document.createParagraph();

    XWPFRun tmpRun = para.createRun();
    tmpRun.setText("LALALALAALALAAAA");

    XWPFAbstractFootnoteEndnote note = para.getDocument().createFootnote();

    XWPFParagraph ipara = note.createParagraph();
    XWPFRun irun = ipara.createRun();
    irun.setText("In the footnote");

    String href = "https://www.garshol.priv.no";
    CTHyperlink hyperlink = ipara.getCTP().addNewHyperlink();
    String rId = ipara.getDocument().getPackagePart().addExternalRelationship(href, XWPFRelation.HYPERLINK.getRelation()).getId();
    hyperlink.setId(rId);

    XWPFHyperlinkRun hyperlinkRun = new XWPFHyperlinkRun(
      hyperlink, CTR.Factory.newInstance(), ipara);
    CTR run = hyperlink.addNewR();
    run.addNewT().setStringValue("And here is a link");

    ipara.addRun(hyperlinkRun);

    para.addFootnoteReference(note);

    document.write(new FileOutputStream(new File("fuck.docx")));
    document.close();
  }
}

We've figured out that the problem is that this file is missing inside the .docx: word/_rels/footnotes.xml.rels. It should contain this XML:

<Relationships xmlns="http://schemas.openxmlformats.org/package/2006/relationships">
  <Relationship Id="rId3"
    Type="http://schemas.openxmlformats.org/officeDocument/2006/relationships/hyperlink"
    Target="https://www.garshol.priv.no"
    TargetMode="External"/>
</Relationships>

If I add that, Word will open the document.

The big question is ... why doesn't Apache POI add this file? What can I do to make it add the file with the correct content? (I've tried Apache POI 5.2.5 and 5.5.1, same result.)

Solution

The problem is that you're adding the hyperlink relationship to the wrong package part. When you call:

ipara.getDocument().getPackagePart().addExternalRelationship(...)

This adds the relationship to word/_rels/document.xml.rels (the main document's relationships), but footnotes live in a separate part (word/footnotes.xml) and need their relationships in word/_rels/footnotes.xml.rels.

You need to add the relationship to the footnotes package part, not the document's package part

so instead of

String rId = ipara.getDocument().getPackagePart().addExternalRelationship(href, XWPFRelation.HYPERLINK.getRelation()).getId();

yo need

String rId = document.getFootnotes().getPackagePart().addExternalRelationship(href, XWPFRelation.HYPERLINK.getRelation()).getId();