如何基于JsonArray的键值过滤列表

Question

How can I filter a list based on the values of the JSONArray ?

JSONArray has the elements which is in simple json structure with key and values.

JSONArray is from the package org.json and using this dependency

             <dependency>
               <groupId>org.json</groupId>
               <artifactId>json</artifactId>
               <version>20180130</version>
            </dependency>

The string response I get when I hit an endpoint is parsed in this way

   String response = [{"ID": 1,"updatedAt": "2019-04-12T09:09:48"},{"ID": 2,"updatedAt": "2019-04-12T09:09:48"}      
   JSONArray jsonArray =  new JSONArray(response)

The list I want to filter consists of list of json strings List<String> eventDataSetList

Now how can I filter the list using the value of key ID from jsonArray in a better way than this?

Here is what I have done so far, But I really don't want to use nested loop:

Map<Object, String> filteredEvents = new HashMap<>();
for (String event : eventDataSetList) {
    for (Object obj : jsonArray) {
        JSONObject jsonObject = (JSONObject) obj;
        if (event.contains(jsonObject.getString("ID"))) {
            filteredEvents.put(jsonObject, event);
        }
    }
}

Answer 1

You can use Java Stream API with this:

Map<JSONObject, String> filteredEvents = StreamSupport.stream(jsonArray.spliterator(), false).map(o -> (JSONObject) o)
        .flatMap(o -> eventDataSetList.stream().filter(e -> e.contains(o.getString("ID"))).map(e -> new AbstractMap.SimpleEntry<>(o, e)))
        .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue));

This creates a Stream, which iterates over all elements in your JSON array and finds all events matching the condition event.contains(jsonObject.getString("ID")) . Finally they are collected to a Map.