REST ASSURED (JAVA): Extract json object value given it's parent object value

I am not sure if this solution will be what you are looking for but you can definitely extract the first name based on the id.

Use JsonPath library in Rest Assured. You can either pass JSON as a String JsonPath.from("json string") or you can get it from Response like this:

JsonPath path = response.jsonPath();

Then, you can get data array and iterate over its elements like this:

    List<HashMap<String, Object>> data = path.getList("data");
    for (HashMap<String, Object> singleObject : data) {
        if (singleObject.get("id").equals(6)) {
            System.out.println(singleObject.get("first_name"));
        }
    }

The above will print name "Tracey" to the console. You can either work with this code or create a method to return parameter based on id like this:

    private static String getFirstNameById(JsonPath path, int id) {
        List<HashMap<String, Object>> data = path.getList("data");
        for (HashMap<String, Object> singleObject : data) {
            if (singleObject.get("id").equals(id)) {
                return (String) singleObject.get("first_name");
            }
        }
        throw new NoSuchElementException(String.format("Can't find first_name with id: %d", id));
    }

Just to make sure you understand - each of the element in data array is JSON Object. We collector all of the objects with method getList. Each of the object is represented by HashMap of String and Object because it contains different types. first_name is String and id is Integer, that's why we have to use HashMap of Objects as second generic argument.

Then we iterate over the HashMap, comparing id of each JSON Object to get desired results.

You can also use Java Stream if you'd like. The same method would look like this:

List<HashMap<String, Object>> data = JsonPath.from(json).getList("data");
Optional<String> firstName = data.stream().filter(x -> x.get("id").equals(6)).map(x -> (String) x.get("first_name")).findFirst();
if (firstName.isPresent()) {
    System.out.println(firstName.get());
}

Use below JsonPath, it will give you first_name based on id:

[?(@.id ==4)].first_name