ArrayList arrayList = (ArrayList) jsonObject.get(category);

This will throw a ClassCastException.

java.lang.ClassCastException: class org.json.JSONArray cannot be cast to class java.util.ArrayList (org.json.JSONArray is in unnamed module of loader org.springframework.boot.loader.LaunchedURLClassLoader @23ab930d; java.util.ArrayList is in module java.base of loader 'bootstrap')

This is because your JSON contains an array. So create a JSONArray and iterate over it.

JSONArray jsonArray = jsonObject.getJSONArray(category);

ArrayList<Object> arrayList = new ArrayList<Object>();
if (jsonArray != null) {
    for (int i=0; i<jsonArray.length(); i++){
        arrayList.add(jsonArray.get(i));
        System.out.println("Adding to the list {}", jsonArray.get(i));
    }
}

The post Class cast exception [JSONArray cannot be cast to org.json.simple.JSONObject] first appeared on Student Projects.

Converting List<Long> to long[]

List input = getSomeLongs(); // Assume some values
long[] output = new long[input.size()];
int index = 0;
for(Long val : input) {
	indexess[index] =  val;
	index++;
} 

Converting long[] to List<Long>

long[] input = getSomeLongs(); // Assume some values
List output = new ArrayList();
for(long val : input){
	lst.add(val);
}

The post How to convert List – Long to long or vise versa? first appeared on Student Projects.