FlattenJSON.groovy

@Grab(group='com.fasterxml.jackson.core', module='jackson-databind', version='2.3.3')

import com.fasterxml.jackson.databind.JsonNode
import com.fasterxml.jackson.databind.ObjectMapper
import com.fasterxml.jackson.databind.node.ArrayNode
import com.fasterxml.jackson.databind.node.ObjectNode
import com.fasterxml.jackson.databind.node.ValueNode

import org.pentaho.di.core.row.*
import org.pentaho.di.core.row.value.*

def addKeys(String currentPath, JsonNode jsonNode, Map<String, String> map) {
    if (jsonNode.isObject()) {
      ObjectNode objectNode = (ObjectNode) jsonNode
      Iterator<Map.Entry<String, JsonNode>> iter = objectNode.fields()
      pathPrefix = currentPath.isEmpty() ? "" : currentPath + ".";

      while (iter.hasNext()) {
        Map.Entry<String, JsonNode> entry = iter.next();
        addKeys(pathPrefix + entry.getKey(), entry.getValue(), map);
      }
    } else if (jsonNode.isArray()) {
      ArrayNode arrayNode = (ArrayNode) jsonNode;
      for (int i = 0; i < arrayNode.size(); i++) {
        addKeys(currentPath + "[" + i + "]", arrayNode.get(i), map);
      }
    } else if (jsonNode.isValueNode()) {
      ValueNode valueNode = (ValueNode) jsonNode;
      map.put(currentPath, valueNode.asText());
    }
}
    
map = [:]
try {
   node = new ObjectMapper().readTree(json)
   addKeys("", node, map );
} catch (IOException e) {
    e.printStackTrace();
}
outputRowMeta = _step_.getInputRowMeta().clone();
_step_.stepMeta.stepMetaInterface.getFields( outputRowMeta, _step_.getStepname(), null, null, _step_, _step_.repository, _step_.metaStore );
outputRowMeta.addValueMeta(new ValueMetaString("key"))
outputRowMeta.addValueMeta(new ValueMetaString("value"))
outputRow = RowDataUtil.resizeArray( row, outputRowMeta.size()+2 )

// Inject at the end
int outputIndex = rowMeta.size()
int count = 1
int numProps = map.size()
key = null
value = null
map.each {kv ->
  if(count < numProps) {
    keyIndex = outputIndex
    valueIndex = outputIndex+1
    if(keyIndex >= 0 && valueIndex >= 0) {
      outputRow[keyIndex] = kv.key
      outputRow[valueIndex] = kv.value
    }
    _step_.putRow(outputRowMeta, outputRow)
  }
  else {
    key = kv.key
    value = kv.value
  }
  count++
}