How can i add additional field to each object in array node using jackson java?

I would approach it this way. Since you want to use Jackson.

First of all, I would extend the Master class by adding the services (which seems to be an array with Strings).

So the class would look something like this:

    public class Master
    {
        private String masterName;
        private int rating;
        private List<String> services = new ArrayList<>(); // THE NEW PART
        
        // Whatever you have else in your class
    }

Then you could get your JSON array, I am supposing that it comes as a String for simplicity. Serialize this array in an array with Master objects and then you can add the services as said above.

e.g.

    String yourJsonString = "[{\"masterName\":\"Bruce\",\"rating\":30},{\"masterName\":\"Tom\",\"rating\":25}]";
    ObjectMapper mapper = new ObjectMapper();

    mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);

    List<Master> theListOfMasters = new ArrayList<>();

    // Read them and put them in an Array
    Master[] mastersPlainArr = mapper.readValue(yourJsonString, Master[].class);

    theListOfMasters = new ArrayList(Arrays.asList(mastersPlainArr));

    // then you can get your masters and edit them..

    theListOfMasters.get(0).getServices.add("A NEW SERVICE...");

    // And so on...

    // Then you can turn them in a JSON array again:

    String json = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(theListOfMasters);