Unable to merge streams with PDFBox - pdf

Question

Currently i am able to merge two PDF files when using java.io.File but unable to do merge them when using input and outputstreams.
Below the code works and generates merged PDF with success.
File mainDoc = new File(path...);
File additionalDoc = new File(path...);
PDFMergerUtility pdfMerger = new PDFMergerUtility();
pdfMerger.setDestinationFileName(path + "/merged.pdf");
pdfMerger.addSource(mainDoc);
pdfMerger.addSource(additionalDoc);
pdfMerger.mergeDocuments(null);
I then tried to do the same by using streams.
ByteArrayOutputStream out = new ByteArrayOutputStream();
InputStream mainDocStream = new FileInputStream(path...);
InputStream additionalDocSteam = new FileInputStream(path...);
PDFMergerUtility pdfMerger = new PDFMergerUtility();
pdfMerger.addSource(mainDocStream);
pdfMerger.addSource(additionalDocSteam);
pdfMerger.setDestinationStream(out);
pdfMerger.mergeDocuments(null);
The code above when reaching line pdfMerger.mergeDocuments(null); throws following exception :
java.io.IOException: Error: End-of-File, expected line at
org.apache.pdfbox.pdfparser.BaseParser.readLine(BaseParser.java:1119)
at
org.apache.pdfbox.pdfparser.COSParser.parseHeader(COSParser.java:2005)
at
org.apache.pdfbox.pdfparser.COSParser.parsePDFHeader(COSParser.java:1988)
at org.apache.pdfbox.pdfparser.PDFParser.parse(PDFParser.java:269)
at org.apache.pdfbox.pdmodel.PDDocument.load(PDDocument.java:1143)
at org.apache.pdfbox.pdmodel.PDDocument.load(PDDocument.java:1059)
at
org.apache.pdfbox.multipdf.PDFMergerUtility.mergeDocuments(PDFMergerUtility.java:263)
At last i tried to follow this answer (Merge Pdf Files Using PDFBox) as an example but my generated pdf does not seem to have merged those two pdfs.
This is the code that i tried.
public InputStream createPDF() {
try{
// Note, i have also tried to use java.io.File instead of an
// InputStream but the result was the same
// File mainDoc = new File(path...);
// PDDocument document = PDDocument.load(mainDoc);
InputStream pdfInputStream = null;
InputStream mainDocStream = new FileInputStream(path...);
PDDocument document = PDDocument.load(mainDocStream);
InputStream additionalDocSteam = new FileInputStream(path...);
PDDocument additionalDocument = PDDocument.load(additionalDocSteam);
PDFMergerUtility pdfMerger = new PDFMergerUtility();
pdfMerger.appendDocument(additionalDocument, document);
document.save(out);
document.close();
PDDocument.load(out.toByteArray());
pdfInputStream = new ByteArrayInputStream(out.toByteArray());
}catch(...){
....
}
return pdfInputStream;
}
The code above does generate a PDF but the newly created PDF contains only the content of the main document and not from the second one. So it looks that i am missing something and the documents are not merged.

Answer 1

I was able to find a solution, but i still cannot understand what is going wrong when using streams. In detail:
While the following code throws an exception (java.io.IOException: Error: End-of-File, expected line) :
ByteArrayOutputStream out = new ByteArrayOutputStream();
InputStream mainDocStream = new FileInputStream(path...);
InputStream additionalDocStream = new FileInputStream(path...);
PDFMergerUtility pdfMerger = new PDFMergerUtility();
pdfMerger.addSource(mainDocStream);
pdfMerger.addSource(additionalDocStream);
pdfMerger.setDestinationStream(out);
pdfMerger.mergeDocuments(null);
When using a File in the addSource method, everything seems to work as required.
public InputStream createPDF() {
InputStream pdfInputStream = null;
try{
File mainDoc = new File(...);
File additionalDoc = new File(path...);
PDFMergerUtility pdfMerger = new PDFMergerUtility();
pdfMerger.addSource(mainDoc);
pdfMerger.addSource(additionalDoc);
pdfMerger.setDestinationStream(out);
pdfMerger.mergeDocuments(null);
pdfInputStream = new ByteArrayInputStream(out.toByteArray());
}catch(...){
...
}
return pdfInputStream;
}
Now, why the first approach using streams throws an exception while using directly the file works, is something i would also like to know.