JSON.stringify() throws an exception

Question

I am building a JavaScript Object from messageCache, but when I use JSON.stringify(), it throws this exception:

EvaluatorException: Java class "[Ljava.lang.reflect.Constructor;" has no public instance field or method named "toJSON"

 

Answer 1

JSON.stringify() is a JavaScript function, and it only accepts JavaScript types.  This error occurs when a Java object (likely a Java String from a messageCache.getValue()) is added as an attribute in your JavaScript object.

The short answer is to convert the values to a JavaScript type object like this:

var newMessage = {};

newMessage.firstName = "" + messageCache.getValue("firstName");

newMessage.middleName = "" + messageCache.getValue("middleName");

newMessage.lastName = "" + messageCache.getValue("lastName");

qie.info(JSON.stringify(newMessage));

 

By prepending the value with an empty string, it converts it to be a JavaScript string, and this will work.

 

After some additional research, JSON.stringify has a "replacer" parameter which we can be use to convert Java objects into JavaScript equivilants.  This can be done like this:

var replacer = function(key, value) {

   var returnValue = value;

   try {

      if (value.getClass() !== null) { // If Java Object

         // qie.debug(key + ': value.getClass() = ' + value.getClass());

         if (value instanceof java.lang.Number) {

            returnValue = 1 * value;

         } else if (value instanceof java.lang.Boolean) {

            returnValue = value.booleanValue();

         } else { // if (value instanceof java.lang.String) {

            returnValue = '' + value;

         }

      }

   } catch (err) {

      // No worries... not a Java object

   }

   return returnValue;

};

 

qie.info(JSON.stringify(newMessage, replacer));

I have uploaded a sample channel configuration with a more complete example:

https://www.qvera.com/kb/?qa=blob&qa_blobid=9646539009203029991

 

 

 

 

Answer 2

Another non-replacer way is to use the Javascript new String() constructor:

var newMessage = {};
newMessage.firstName = new String( messageCache.getValue("firstName"));
newMessage.middleName = new String( messageCache.getValue("middleName"));
newMessage.lastName = new String( messageCache.getValue("lastName"));
qie.info(JSON.stringify(newMessage));

Doing the same thing: forcing conversion of a Java string to a Javascript string

 

(Personally, I'd prefer

    var newMessage = {
        firstName: new String( messageCache.getValue("firstName")),
        middleName: new String( messageCache.getValue("middleName")),
        lastName: new String( messageCache.getValue("lastName")),
    }
    qie.info(JSON.stringify(newMessage));

but that's me.)