通过使用 lambda 表达式和 Java 从 88677344588 的 ArrayList 中提取 HashMap 8

Question

I need to find a Hashmap whose is_default value is equal to 1.

Noted: In this structure, only 1 hashmap contains is_default value is equal to 1.

Answer 1

You only need to check those maps that contain the required key. After that, you need to choose from them the one with the desired value of this key. It can be done with filter

list.stream()
    .filter(x -> x.containsKey("is_default"))
    .filter(x -> x.get("is_default")
                  .compareTo(BigDecimal.ONE) == 0)
    .forEach(System.out::println);

Or you can use getOrDefault and specify wrong value as default to skip those maps that do not contain a key

list.stream()
    .filter(x -> x.getOrDefault("is_default", BigDecimal.ZERO)
                  .compareTo(BigDecimal.ONE) == 0)
    .forEach(System.out::println);

Example

public static void main(String[] args) {
    List<Map<String, BigDecimal>> list = new ArrayList<>();

    // target
    Map<String, BigDecimal> map = new HashMap<>();
    map.put("is_default", BigDecimal.ONE);
    map.put("key", BigDecimal.TEN);
    list.add(map);

    Map<String, BigDecimal> map2 = new HashMap<>();
    map2.put("is_default", BigDecimal.ZERO);
    map2.put("key", BigDecimal.ZERO);
    list.add(map2);

    Map<String, BigDecimal> map3 = new HashMap<>();
    map3.put("isnt_default", BigDecimal.ZERO);
    list.add(map3);

    list.stream()
        .filter(x -> x.containsKey("is_default"))
        .filter(x -> x.get("is_default")
                      .compareTo(BigDecimal.ONE) == 0)
        .forEach(System.out::println);
}

Output

{is_default=1, key=10}

Answer 2

Try this.

public static void main(String[] args) {
    List<Map<String, String>> list = List.of(
        Map.of("is_default", "0", "label", "test0"),
        Map.of("is_default", "1", "label", "test1"),
        Map.of("is_default", "2", "label", "test2"));
    Map<String, String> extracted = list.stream()
        .filter(map -> Objects.equals(map.get("is_default"), "1"))
        .findFirst().orElse(null);
    System.out.println(extracted);
}

output:

{label=test1, is_default=1}