从映射中获取 Java 中特定键的长值列表

Question

I have a Map: Map<String, Object> data The content is:

{"id_list":["2147041","2155271","2155281"],
 "remoteHost":"127.0.0.1",
 "userId":"user",
 "agencyId":1}

I want to store in a Long List, all the values with Key: id_list It would be:

list:[2147041,2155271,2155281] Is there a way to do that? I've got:

List<Long> list = new ArrayList<Long>(data.get("id_list") );

Answer 1

new ArrayList<Long>(Arrays.asList(data.get("id_list")));

Assuming that is an array in your hashMap. Otherwise you'd have to cast it as an (Iterable<String>)data.get("id_list"); and add each String one by one.

Answer 2

It looks like the values in the collection of id_list are String objects, so you should be able to do it with a loop that performs conversions:

Iterable<String> idStrings = (Iterable<String>)data.get("id_list");
List<Long> list = new ArrayList<Long>();
for (String id : idStrings) {
    list.add(Long.valueOf(id));
}

Answer 3

You can use Arrays.asList to instantiate from that array

List<Long> list = Arrays.asList(data.get("id_list"));

or if you want a new ArrayList instead of just a genericl List

List<Long> list = new ArrayList<Long>(Arrays.asList(data.get("id_list")));

Answer 4

If running on Java 8 or later , you may use a BiFunction for this:

  

  private BiFunction<Map<String, Object>, String, List<Long>> convertToLong() {
    return (thatMap, targetKey) -> thatMap.get(targetKey).stream()
          .map(id -> Long.valueOf(id))
          .collect(Collectors.toList());
  }

    // The call

    String targetKey = "id_list";
    // prepare the values of this accordingly.
    Map<String, Object> thatMap = new HashMap<>();

    List<Long> converted = convertToLong().apply(thatMap, targetKey)
    
    // Assumption for the output: your map contains the sample data provided here.
    System.out.println("converted: " + converted); //=> [2147041, 2155271, 2155281]