Get values in a List from JSON

Question

I'm doing a REST API call to get the global value set and trying to deserialize the JSON result to get the picklist values in a List.

Here is the JSON:

 {
  "size": 1,
  "totalSize": 1,
  "done": true,
  "queryLocator": null,
  "entityTypeName": "GlobalValueSet",
  "records": [
    {
      "attributes": {
        "type": "GlobalValueSet",
        "url": "/services/data/v53.0/tooling/sobjects/GlobalValueSet/0Nt59000000AAAAAAA"
      },
      "Metadata": {
        "customValue": [
          {
            "color": null,
            "default": false,
            "description": null,
            "isActive": null,
            "label": "USA",
            "urls": null,
            "valueName": "USA"
          },
          {
            "color": null,
            "default": false,
            "description": null,
            "isActive": null,
            "label": "Canada",
            "urls": null,
            "valueName": "Canada"
          }
        ],
        "description": null,
        "masterLabel": "Countries",
        "sorted": false,
        "urls": null
      },
      "Id": "0Nt59000000AAAAAAA"
    }
  ]
}

I need help in fixing the error and also how to get valueNames in a List

Error: System.JSONException: Malformed JSON: Expected '{' at the beginning of an object.

Here is what I have tried so far:

Wrapper:

Here is my original wrapper that covers all blocks but still throwing the same error.    

public class GlobalValueSetWrapper{
    public Integer size;
    public Integer totalSize;
    public boolean done;
    public QueryLocator queryLocator;
    public String entityTypeName;
    public List<Records> records;

    class QueryLocator {
    }

    class Records {
        public Attributes attributes;
        public Metadata Metadata;
        public String Id;
    }
    
    class Attributes {
        public String type; 
        public String url;  
    }
    
    class Metadata {
        public List<CustomValue> customValue;
        public Description description;
        public String masterLabel;
        public boolean sorted;
        public URLs urls;
    }

    class CustomValue {
        public Color color;
        public boolean default;
        public Description description;
        public IsActive isActive;
        public String label;
        public URLs urls;
        public String valueName;    
    }

    class Color {
    }
    class Description {
    }
    class IsActive {
    }
    class URLs {
    }

    public static GlobalValueSetWrapper parse(String json){
        return (GlobalValueSetWrapper) System.JSON.deserialize(json, GlobalValueSetWrapper.class);
    }

Class:

//calling API to get the JSON result
HttpResponse res = GlobalValueSetAPIHandler.getResponse('Countries');
GlobalValueSetWrapper wrapper = (GlobalValueSetWrapper) JSON.deserialize(res.getBody(), GlobalValueSetWrapper.class);

Answer 1

The reason is, your wrapper is only written for the parsing of metadata block. However, there is another block ahead of the metadata block.

A sample route would be current JSON like below - object.records[0].Metadata then your logic will work.

You can easily generate wrappers using https://json2apex.herokuapp.com/, those will work without hiccups.

Or if you need only metadata block, then you have to write other processing code to get that block as a string using either Maps or other means.

Answer 2

I'm able to fix this.

I forgot to give public to the classes.

Solution to get Global Picklist values from HttpResponse:

public class GlobalValueSetWrapper{
    public List<Records> records;

    public class Records {
        public Metadata metadata;
    }
    
    public class Metadata {
        public List<CustomValue> customValue;
    }

    public class CustomValue {
        public String label;
        public String valueName;    
    }

    public static List<String> getPicklistValues(HttpResponse response){
        List<String> picklistValues = new List<String>();
        
        GlobalValueSetWrapper wrapper = (GlobalValueSetWrapper) System.JSON.deserialize(response.getBody(), GlobalValueSetWrapper.class);
        
        for(GlobalValueSetWrapper.customValue value : wrapper.records[0].metadata.customValue){
            picklistValues.add(value.valueName);
            system.debug('Piclist Value: ' + value.valueName);
        }
        system.debug('Piclist Values: ' + picklistValues);
        
        return picklistValues;
    }
}