Chris, Unfortunately, at this time, the EvaluateJsonPath requires that the JSON to evaluate be the content of the FlowFIle. There already does exist a ticket [1] that would allow you to specify an attribute to use as the JSON instead of requiring that it be the content only. Unfortunately, this has not yet been implemented.
Thanks -Mark [1] https://issues.apache.org/jira/browse/NIFI-1567 > On Mar 21, 2016, at 1:48 PM, McDermott, Chris Kevin (MSDU - > STaTS/StorefrontRemote) <[email protected]> wrote: > > Joe, > > Thanks for the reply. I think I was not clear. > > The JSON I need to evaluate is in a FlowFile attribute (kafka.key) which I > need to be able to evaluate without modifying the original FlowFile content > (which was read from the Kafka topic). What I can’t figure out is how to > squirrel away the flowfile content so that I can write the value of the > kafka.key attribute to the FlowFile content, so that I can process it with > EvaluateJsonPath, and then read content I squirreled away back into the > FlowFile content. I considered using the the DistributedMapCache, but there > would be no guarantee what I added to the cache would still be there when I > needed it back. > > > > > On 3/21/16, 1:37 PM, "Joe Witt" <[email protected]> wrote: > >> Chris, >> >> Sounds like you have the right flow in mind already. EvaluateJSONPath >> does not write content. It merely evaluates the given jsonpath >> expression against the content of the flowfile and if appropriate >> creates a flowfile attribute of what it finds. >> >> For example if you have JSON from Twitter you can use EvaluateJsonPath >> and add a property with a name >> 'twitter.user' and a value of '$.user.name' >> >> Once you run the tweets through each flow file will have an attribute >> called 'twitter.user' with the name found in the message. No >> manipulation of content at all. Just promotes things it finds to flow >> file attributes. >> >> Thanks >> Joe >> >> On Mon, Mar 21, 2016 at 1:34 PM, McDermott, Chris Kevin (MSDU - >> STaTS/StorefrontRemote) <[email protected]> wrote: >>> What I need to do is read a file from Kafka. The Kafka key contains a JSON >>> string which I need to turn in FlowFile attributes while preserving the >>> original FlowFile content. Obviously I can use EvaluteJsonPath but that >>> necessitates replacing the FlowFile content with the kaka.key attribute, >>> thus loosing the original FlowFile content. I feel like I’m missing >>> something fundamental.
