使用Sejda合并PDF失败，流输出

Question

Using Sejda 1.0.0.RELEASE, I basically followed the tutorial for splitting a PDF but tried merging instead ( org.sejda.impl.itext5.MergeTask , MergeParameters , ...). All works great with the FileTaskOutput :

parameters.setOutput(new FileTaskOutput(new File("/some/path/merged.pdf")));

However I am unable to change this to StreamTaskOutput correctly:

OutputStream os = new FileOutputStream("/some/path/merged.pdf");
parameters.setOutput(new StreamTaskOutput(os));
parameters.setOutputName("merged.pdf");

No error is reported, but the resulting file cannot be read by Preview.app and is approximately 31 kB smaller (out of the ~1.2 MB total result) than the file saved above.

My first idea was: stream is not being closed properly! So I added os.close(); to the end of CompletionListener , still the same problem.

Remarks:

• The reason I need to use StreamTaskOutput is that this merge logic will live in a web app, and the merged PDF will be sent directly over HTTP. I could store the temporary file and serve that one, but that is a hack.
• Due to licencing issues, I cannot use the iText 5 version of the task.

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Edit

Turns out, the reason is that StreamTaskOutput zips the result into a ZIP file! OutputWriterHelper.copyToStream() is the culprit. If I rename merged.pdf to merged.zip , it's a valid ZIP file containing a perfectly valid merged.pdf file!

Could anyone (dear authors of the library) comment on why this is happening?

Answer 1

The idea is that when a task consumes a MultipleOutputTaskParameters producing multiple output documents, the StreamTaskOutput has to group them to be able to write all of them to a stream output. Unfortunately Sejda currently applies the same logic to SingleOutputTaskParameters , hence your issue. We can fix this in Sejda 2.0 because it makes more sense to directly stream the out document in case of SingleOutputTaskParameters . For Sejda 1.x I'm not sure how to address this remaining compatible with the existing behaviour.