[Java] Stream > Filter

Git

https://github.com/ymwoo88/stream/tree/feature/filter-%EC%98%88%EC%A0%9C

설명

Stream의 Filter API는 Predicate에서 true를 반환하는 데이터만 존재하는 Stream을 리턴하는 기능을 제공합니다.

• filter는 and조건으로 중첩적용이 가능하나 or조건은 사용되지 않습니다.

Filter

Stream<T> filter(Predicate<? super T> predicate);

예제

• 샘플 데이터

  @Getter
  @Builder
  @NoArgsConstructor
  @AllArgsConstructor
  @ToString
  public class User {
    private Long id;
    private String name;
    private String email;
    private Integer age;
  
    public static User getUserAmil() {
        return User.builder()
                .id(1L)
                .name("amil")
                .email("amil@ymwoo.com")
                .age(35)
                .build();
    }
  
    public static User getUserBenny() {
        return User.builder()
                .id(2L)
                .name("benny")
                .email("benny@ymwoo.com")
                .age(29)
                .build();
    }
  
    public static User getUserCho() {
        return User.builder()
                .id(3L)
                .name("cho")
                .email("cho@ymwoo.com")
                .age(33)
                .build();
    }
  
    public static List<User> getExamUserList() {
        return Arrays.asList(getUserAmil(), getUserCho(), getUserBenny());
    }
  }

• 예제1) 단건 필터링

    @Test
    @DisplayName("user name이 amil 인경우 필터링")
    void case1() {
        List<User> examUserList = User.getExamUserList();
        List<User> filteredUser = examUserList
                .stream()
                .filter(user -> "amil".equals(user.getName()))
                .toList();
        // 결과 출력
        filteredUser
                .forEach(user -> log.info(">>> Filtered User Info = {}", user));
    }

  15:30:32.130 [Test worker] INFO com.ymwoo.stream.filter.StreamFilterTest -- >>> Filtered User Info = User(id=1, name=amil, email=amil@ymwoo.com, age=35)

• 예제2) 다건 필터링

    @Test
    @DisplayName("30대 이하이면서 일하는 중인경우 필터링")
    void case2() {
        List<User> examUserList = User.getExamUserList();
        List<User> filteredUser = examUserList
                .stream()
                .filter(user -> 30 > user.getAge())
                .filter(User::getIsWorking)
                .toList();
        // 결과 출력
        filteredUser
                .forEach(user -> log.info(">>> Filtered User Info = {}", user));
    }

  15:52:12.338 [Test worker] INFO com.ymwoo.stream.filter.StreamFilterTest -- >>> Filtered User Info = User(id=1, name=amil, email=amil@ymwoo.com, age=25, isWorking=true)
  15:52:12.345 [Test worker] INFO com.ymwoo.stream.filter.StreamFilterTest -- >>> Filtered User Info = User(id=2, name=benny, email=benny@ymwoo.com, age=29, isWorking=true)

참조

https://backtony.github.io/java/2022-02-06-java-46/