ExecuteScript - JSON-to-JSON Revisited (with Javascript)

A question came in on the Apache NiFi users group about doing things with ExecuteScript using something other than Groovy (specifically, Javascript). I put a fairly trivial example inside a previous post, but it doesn't cover one of the most important features, overwriting flow file content.

One major difference between Groovy and Javascript here is that you will want to get a reference to Java objects using Java.type(), in order to create new objects, invoke static methods, etc. I use the following in the script below:

var StreamCallback =  Java.type("org.apache.nifi.processor.io.StreamCallback")
var IOUtils = Java.type("org.apache.commons.io.IOUtils")
var StandardCharsets = Java.type("java.nio.charset.StandardCharsets")

Also, the Javascript engine has something very much like closure coercion in Groovy. If you are creating a new anonymous object from a class/interface, and that class/interface has a single method, you can provide a Javascript function (with the appropriate arguments) in the object constructor. So to create an implementation of StreamCallback (used in session.write() to overwrite the contents of a flowfile), you have:

new StreamCallback(function(inputStream, outputStream) { /* Do stuff */ })

With that in mind, I recreated the JSON-to-JSON example from my previous post, this time using Javascript as the language.  The script is as follows:

var flowFile = session.get();
if (flowFile != null) {

  var StreamCallback =  Java.type("org.apache.nifi.processor.io.StreamCallback")
  var IOUtils = Java.type("org.apache.commons.io.IOUtils")
  var StandardCharsets = Java.type("java.nio.charset.StandardCharsets")

  flowFile = session.write(flowFile,
    new StreamCallback(function(inputStream, outputStream) {
        var text = IOUtils.toString(inputStream, StandardCharsets.UTF_8)
        var obj = JSON.parse(text)
        var newObj = {
          "Range": 5,
          "Rating": obj.rating.primary.value,
          "SecondaryRatings": {}
        }
        for(var key in obj.rating){
          var attrName = key;
          var attrValue = obj.rating[key];
          if(attrName != "primary") {
            newObj.SecondaryRatings[attrName] = {"id": attrName, "Range": 5, "Value": attrValue.value};
          }
        }
        outputStream.write(JSON.stringify(newObj, null, '\t').getBytes(StandardCharsets.UTF_8)) 
    }))
  flowFile = session.putAttribute(flowFile, "filename", flowFile.getAttribute('filename').split('.')[0]+'_translated.json')
  session.transfer(flowFile, REL_SUCCESS)
}

The template is available a Gist (here), please let me know how/if this works for you.  Cheers!

UPDATE: This script works with Nashorn (Java 8's Javascript engine), but doesn't work if you're using Java 7 (Rhino).  Here's an equivalent script for Java 7 / Rhino:

importClass(org.apache.commons.io.IOUtils)
importClass(java.nio.charset.StandardCharsets)
importClass(org.apache.nifi.processor.io.StreamCallback)
var flowFile = session.get();
if (flowFile != null) {

flowFile = session.write(flowFile,
        new StreamCallback() {process : function(inputStream, outputStream) {
            var text = IOUtils.toString(inputStream, StandardCharsets.UTF_8)
     var obj = JSON.parse(text)
            var newObj = {
  "Range": 5,
  "Rating": obj.rating.primary.value,
  "SecondaryRatings": {}
     }
     for(var key in obj.rating){
             var attrName = key;
             var attrValue = obj.rating[key];
    if(attrName != "primary") {
     newObj.SecondaryRatings[attrName] = {"id": attrName, "Range": 5, "Value": attrValue.value};
  }
            }
    outputStream.write(new java.lang.String(JSON.stringify(newObj, null, '\t')).getBytes(StandardCharsets.UTF_8)) 
        }})
flowFile = session.putAttribute(flowFile, "filename", flowFile.getAttribute('filename').split('.')[0]+'_translated.json')
session.transfer(flowFile, REL_SUCCESS)
}