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From Mark Payne <>
Subject Re: Coding a Processor that writes to multiple output flowfiles at once
Date Mon, 23 Nov 2015 14:18:35 GMT
Hey Salvatore,

I think the key piece that you are missing is the ProcessSession.append() method. You can
use this efficiently append to FlowFile A, then to FlowFile B, then to FlowFile A, then to
FlowFile C,
or what-have-you. A good example that comes to mind is the RouteText Processor. This is available
on the 'master' branch.

So the overall logic would look something like:

List<FlowFile> flowFiles = new ArrayList<>();
for (int i=0; i < numColumns; i++) {
    FlowFile colFlowFile = session.create(originalFlowFile);

// read line of text, new InputStreamCallback() {
      void process(final InputStream rawIn) {
          try (final BufferedReader in = new BufferedReader(new InputStreamReader(rawIn)))
		String line = in.readLine();

		String[] columns = line.split(",");
		for (int i=0; i < columns.length; i++) {
			FlowFile colFlowFile = flowFiles.get(i);
			colFlowFile = session.append(colFlowFile, new OutputStreamCallback() {
         			void process(final OutputStream out) {

			flowFiles.set(i, colFlowFile);

But as mentioned, the RouteText processor is a great full processor to use as an example.

Let us know if you run into any more problems!


> On Nov 23, 2015, at 2:40 AM, Salvatore Papa <> wrote:
> Heya NiFi devs,
> I'm having a bit of trouble trying to wrap my head around a valid way of
> tackling this problem with the available Processor templates. I'd like to
> split an input flowfile into N different flowfiles, 1 going into 1 of N
> relationships.
> A simplistic way of viewing it would be: A very large CSV file, with N
> columns, and I want to split each column into its own flowfile, and each of
> these flowfiles to its own relationship (or with an attribute saying which
> column it belongs to).
> Basic premise is for an example with two columns, and only two lines:
> * Read a line, write first column value to flowfile A, write second column
> value to flowfile B
> * Read next line, appending first column value to flowfile A, appending
> second column value to flowfile B
> Followed by one of:
> * Send flowfile A to relationship A, and send flowfile B to relationship B
> or
> * Set attribute "A" to flowfile A, attribute "B" to flowfile B, then send
> both A and B to a 'success' relationship.
> Unfortunately, I can't seem to find a way to write to multiple flowfiles at
> once, or at least, write to an outputstream for one flowfile, then write to
> another outputstream for another flowfile, then continue writing to the
> first flowfile.
> If they weren't such large files, i'd be okay with reading the input file N
> times, pulling out the different part each time, but i'd like to only have
> to read each line (by extension, the file) only once.
> I've written AbstractProcessors before for simple One-to-One
> transformations, and even Merge processors which use are an extension of
> AbstractSessionFactoryProcessors to do Many-to-One, and even Split
> AbstractProcessors for One-to-Many in serial (splitting at different
> places, even clone(flowfile, start, size); But I can't work out a way to do
> this One-to-Many in parallel.
> Any ideas? Am I missing something useful? Do I just have to do it reading
> it multiple times? Just a really simple proof of concept explaining the
> design would be enough to get me started.
> Kind regards,
> Salvatore

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