https://community.cloudera.com/t5/Support-Questions/Nifi-How-to-add-key-value-to-json/m-p/200909#M162924 <P>In addition to <A rel="user" href="https://community.cloudera.com/users/355/bhagan.html" nodeid="355">@bhagan</A>'s answer, as of NiFi 1.2.0 (due to <A target="_blank" href="https://issues.apache.org/jira/browse/NIFI-3010">NIFI-3010</A>), you can use NiFi Expression Language in JOLT specifications, so with a JoltTransformJSON processor you could have the following Chain spec:</P><PRE>[{ "operation": "default", "spec": { "*": { "ctime": "${now()}" } } }]</PRE><P>If you want the <EM>ctime</EM> field to contain a string with the number of milliseconds since Epoch, you can use now():toNumber() instead of just now(). If you want an actual numeric value (rather than a String containing the numeric value), you need an additional operation to change the value to a long:</P><PRE>[{ "operation": "default", "spec": { "*": { "ctime": "${now():toNumber()}" } } }, {   "operation": "modify-overwrite-beta",   "spec": { "*": {      "ctime": "=toLong" }   } }] </PRE> Fri, 09 Jun 2017 01:36:30 GMT mburgess 2017-06-09T01:36:30Z