Write a generic JSON-serializable Parameters class without hitting "Apex Type unsupported in JSON: Object"

Question

I need to easily serialize (save as long text field in database) and deserialize (convert back to a class) a parameter list in Apex of String -> Object value pairs.

My first idea was just to write a class like this...:

public class Parameters{
    private Map<String, Object> parameters = new Map<String, Object>();

    public void add(String name, Object value) {
        this.parameters.put(name, value);
    }

    public Object get(String name) {
        Object result = null;

        if(this.parameters.containsKey(name)) {
            result = this.parameters.get(name);
        }
        return result;
    }    
} 

... and use JSON.serialize and deserialize..

Parameters params = new Parameters();
params.add('Name', 'Robert');
params.add('Age', 36);
String serialized = JSON.serialize(params);
Parameters deserialized = (Parameters) JSON.deserializeStrict(serialized, Parameters.class);
System.assertEquals(params, deserialized);

but then I got this error message:

System.JSONException: Apex Type unsupported in JSON: Object

Any idea or experience on how to implement such a Parameter class that is able to at least hold all basic (non-collection) types?!

Answer 1

Rational for Error: JSON does not encoded the data types of the data, thus you have to give your class type to allow it to understand how to parse the data as it works its way through the class members. The Object data type is not enough for the deserialize method to know the data type.

Using JSON.deserializeUntyped. To work around this you can manually parse the JSON using the various JSON parser methods or use the deserializeUntyped method which returns conveniently a map that contains primitive data types!

So I've leveraged this in some new methods to encapsulate this with your Parameters class.

public class Parameters{
    private Map<String, Object> parameters = new Map<String, Object>();

    public void add(String name, Object value) {
        this.parameters.put(name, value);
    }

    public Object get(String name) {
        Object result = null;

        if(this.parameters.containsKey(name)) {
            result = this.parameters.get(name);
        }
        return result;
    }    

    public String serialize()
    {
        return JSON.serialize(parameters);      
    }

    public static Parameters deserialize(String serialized)
    { 
        Parameters parameters = new Parameters();
        parameters.parameters = (Map<String, Object>) JSON.deserializeUntyped(serialized);
        return parameters;
    }
}

This is a slightly modified version of your test code to use the new helper methods.

Parameters params = new Parameters();
params.add('Name', 'Robert');
params.add('Age', 36);
String serialized = params.serialize();
Parameters deserialized = Parameters.deserialize(serialized);
System.assertEquals(params.toString(), deserialized.toString());

I've used toString to compare equality, as without it the check fails, as the two variables point to different instances of the same object.

Alternative:

This naked version also works as well...

Map<String, Object> parameters = new Map<String, Object>();
parameters.put('A', 36);
parameters.put('B', 'Robots');
String serialized = JSON.serialize(parameters);
System.debug(serialized);
parameters = (Map<String, Object>) JSON.deserializeUntyped(serialized);
System.debug(parameters.get('B'));