I am pretty new to Java and I am quite found of fonctional programming. Here I am trying to write the most concise factory method to create a List<Manager> based on a JSONArray retrieved from an API. Here is a simplified version of what I have in mind
public List<Manager> getManagers(HashMap parameters) throws IOException, InterruptedException {
JSONArray records = (JSONArray) api.getData("Manager", parameters).get("records");
records.forEach(x -> new Manager(x.get("FirstName"),x.get("LastName")))
and how I would do it in python (I am highly biased)
manager_list = list(map(lambda x: Manager(x["FirstName"],x["LastName"]),records))
I am experiencing two issues.
- access JSONObject fields inside the lambda expression
Despite x being a JSONObject
records.forEach(x -> System.out.println(x.getClass())); class org.json.JSONObject
x.get("FirstName") does not work in the lambda. Is it because .get() is an instance method or am I missing something else?
- easily append
Managersto a list
This does not work
List managers = records.forEach(x -> new Manager(x.get("FirstName"),x.get("LastName")))
because forEach returns void. Does forEach have a cousin who could return any kind of Interable or Collection ?
Since I am new to java, I both interested in implementations for my actual problem and more general discussions on functional programming in modern java
Answer
Try the following:
public List<Manager> getManagers(HashMap parameters) throws IOException, InterruptedException {
JSONArray records = (JSONArray) api.getData("Employee", parameters).get("records");
List<Manager> managers = new ArrayList<>();
records.forEach(jsonRecord -> {
JSONObject record = (JSONObject) jsonRecord;
managers.add(new Manager(record.getString("FirstName"), record.getString("LastName")));
});
return managers;
}
You may have to cast each item into a JSONObject in order to access the properties.