I made my own function to resolve the problem. I will post here to help who has the same problem. If anyone want to help to solve the initial problem, I am still interested.
You can paste the code bellow on your "Modified Java Script Value" step after receive the Json response from service or get that on file. Note that you need to change the name of variables that you want to find on Json.
Result field is a Json Value.
//Script here
function findInArray(myValue, myArray){
var myResult='';
if(myArray.indexOf(myValue) > -1){
myResult = true;
} else {
myResult = false;
}
return myResult;
}
function getAttributeValue(Atribute, Object)
{
start = indexOf(Object,Atribute);
for (i= start; i < Object.length; i++)
{
if (substr(Object,i,1) == ":")
{
start_value = i+1;
break;
}
}
for (i= start_value; i < Object.length; i++)
{
end_value = i;
if (substr(Object,i,1) == ",")
{
break;
}
}
AttributeValue = replace(substr(Object, start_value, end_value-start_value),'"','');
if (indexOf(AttributeValue, "null") >= 0)
{
AttributeValue = null;
}
return AttributeValue ;
}
// Recupera Status
if (findInArray("status",result))
{
var status = getAttributeValue("status", result);
}
else
{
var status = "";
}
// Recupera _ID
if (findInArray("_id",result))
{
var mandrill_id = getAttributeValue("_id", result);
}
else
{
var mandrill_id = "";
}
// Recupera reject_reason
if (findInArray("reject_reason",result))
{
var reject_reason = replace(getAttributeValue("reject_reason", result),"}","");
}
else
{
var reject_reason = "";
}