@renuu You have to build the final values you want as separate key value pairs like this: UpdateAttribute Next you will use these attributes  to create a json object attribute using AttributesToJson:   AttributesToJson flowfile-attribute   After that, if you inspect the flowfile you will see the json object as JSONAttributes:   FlowFile Attribute JSONAttributes   From here you can use it as ${JSONAttributes} or if you need it to be called ${attributes} you just use another UpdateAttribute:   ... View more

@renuu  Create your attributes how you need them to be in UpdateAttribute.   Next use attributesToJson to combine the attributes you want, and put them together into a single json object. In this processor set to flowfile-attribute if you need to use them as attributes later.   If you need to POST the json, use flowfile-content.   Once you have set your attributes in UpdateAttribute, test the flow and view the attributes, or the flowfile content.  You may notice the strings are escaped.  If they are escaped, and you need them to not be escaped, that is when you must use unescapeJson.  You can use unescapeJson anywhere you are allowed to use expression language. You could use it in another UpdateAttribute process to make a new attribute that is unescaped.  You can use it in replaceText if you want to unescape the content of the flowfile before posting.      ... View more

After you posted this new issue, I created a sample like yours, and I had the same error you have above.  Then I added the DistributedMapCacheServer, enabled it, and re-tested my flow.   I created a template for DetectDuplicate which you can find here:   https://github.com/steven-dfheinz/NiFi-Templates/blob/master/DetectDuplicate_DistributedMapCache_Demo.xml   If you install the template, you still have to + ADD the Map Cache Server in the Template's Process Group Controller Services.  The NiFI Template system does not include the server (known bug), it only includes the client.   ... View more