Object received does not correspond to model

I have a problem, but I find it hard to express it. I receive from MQTT a message in byte[], I convert it into a String, then the result is sent to GSON which creates me a JenkinsMqttObject.

String messageToString = message.getPayload().toString();
JenkinsMqttObject monobjet = gson.fromJson(messageToString, JenkinsMqttObject.class);

In the example code, JenkinsMqttObject is very simplified. The problem I have is the following:

MQTT sends me an object which can be :
> "{"value1":20,"value2":40}

But that can also be :
> "{"value1":20,"value2":40,"value3":60}

So depending on the case, I receive an object that contains 2 or 3 attributes.
The problem is that I created a java model like this:

JenkinsMqttObject.class

private String value1;
private String value2;
private String value3;
//getter & setters...

The problem is that i say at GSON that the object received is of type JenkinsMqttObject but it's not all time right !

So i don't know at all, how to be able to receive an object in Java that can correspond or not to a model.

Thanks for help !

You should take help of Map or HashMap for your Model class. It should be similar to the class given below.

class JenkinsMqttObject{
    HashMap<String, String> values;
    //getters & setters
}

You have to modify the main code as below.

String messageToString = message.getPayload().toString();
HashMap<String,String> vmap = new Gson().fromJson(messageToString , new TypeToken<HashMap<String, String>>(){}.getType());
JenkinsMqttObject monobjet = new JenkinsMqttObject();
monobjet.setValues(vmap);

Now if you want to access any value, you can access it as below.

monobjet.getValues().get("value1");

As RLD's answer suggests, Map is the way to go.

You can use TypeToken but you can also declare a specific class to avoid using beforementioned and make parsing even simpler so parse it straight into the map:

public class JenkinsMqttObject extends HashMap<String, Object> {}

Also I do not think that if you put byte[].toString() it will produce you valid JSON but costructing a new String objects from a byte[] will work:

JenkinsMqttObject monobjet = gson.fromJson(new String(message.getPayload()),
                                               JenkinsMqttObject.class);

Then it is just to:

monobjet.get("value1");

as already stated in the comments, when value3 is missing in the json, gson will set value3 to null in the JenkinsMqttObject instance. from gson documentation (emphasis mine):

> - This implementation handles nulls correctly.
>
> - While serializing, a null field is omitted from the output.
> - While deserializing, a missing entry in JSON results in setting the corresponding field in the object to its default value: null for object types, zero for numeric types, and false for booleans.