List列表根据对象的属性进行去重操作

「List列表根据对象的属性进行去重操作」

• 去除List中重复的String
• List中对象的去重
• List中根据对象的属性去重

「一、去除List中重复的String」

方法1：

    /**
     * 去除重复的List 方法一
     *
     * @param sourceList 源List
     * @return
     */
    public static List<String> removeRepeatList(List<String> sourceList) {
        if (CollUtil.isEmpty(sourceList)) {
            return Collections.emptyList();
        }
        Set<String> targetSet = new LinkedHashSet<>();
        targetSet.addAll(sourceList);
        sourceList.clear();
        sourceList.addAll(targetSet);
        return sourceList;
    }

方法2：

     /**
     * 去除重复的List 方法二
     *
     * @param sourceList 源List
     * @return
     */
    public static List<String> removeRepeatListMethod2(List<String> sourceList) {
        if (CollUtil.isEmpty(sourceList)) {
            return Collections.emptyList();
        }
        return sourceList.stream().distinct().collect(Collectors.toList());
    }

「二、List中对象去重」

新建Student类

/**
 * @author 公众号: SimpleMemory
 * @version 1.0.0
 * @ClassName Student.java
 * @Description TODO
 * @createTime 2022年04月16日 12:17:00
 */
@Data
@EqualsAndHashCode
@AllArgsConstructor
public class Student {
    private String userId;
    private String name;
}

主要实现

     /**
     * List中对象去重
     *
     * @param studentList
     * @return
     */
    public static List<Student> removeRepeatStudentList(List<Student> studentList) {
        if (CollUtil.isEmpty(studentList)) {
            return Collections.emptyList();
        }
        List<Student> targetStudentList = new ArrayList<>();
        studentList.stream().forEach(item -> {
                    if (!targetStudentList.contains(item)) {
                        targetStudentList.add(item);
                    }
                }
        );
        return studentList;
    }

「三、List中根据对象的属性进行去重」

方法1：

     /**
     * 根据Student  userId去重
     *
     * @param studentList
     * @return
     */
    public static List<Student> removeRepeatStudentListByUserId(List<Student> studentList) {
        if (CollUtil.isEmpty(studentList)) {
            return Collections.emptyList();
        }
        Set<Student> studentSet = new TreeSet<>((o1, o2) -> o1.getUserId().compareTo(o2.getUserId()));
        studentSet.addAll(studentList);
        return new ArrayList<>(studentSet);
    }

方法2：

     /**
     * 根据Student  userId去重 方法二:Java 8写法
     *
     * @param studentList
     * @return
     */
    public static List<Student> removeRepeatStudentListByUserIdMethod2(List<Student> studentList) {
        if (CollUtil.isEmpty(studentList)) {
            return Collections.emptyList();
        }
        List<Student> targetStudentList = studentList.stream().collect(
                collectingAndThen(
                        toCollection(() -> new TreeSet<>(comparing(Student::getUserId))), ArrayList::new)
        );
        return targetStudentList;
    }

方法3：

/**
     * 根据Student  userId去重 方法三
     *
     * @param studentList
     * @return
     */
    public static List<Student> removeRepeatStudentListByUserIdMethod3(List<Student> studentList) {
        if (CollUtil.isEmpty(studentList)) {
            return Collections.emptyList();
        }
        return studentList.stream().filter(distinctByKey(p -> p.getUserId())).collect(Collectors.toList());
    }


    public static <T> Predicate<T> distinctByKey(Function<? super T, Object> keyExtractor) {
        Map<Object, Boolean> map = new ConcurrentHashMap<>();
        return t -> map.putIfAbsent(keyExtractor.apply(t), Boolean.TRUE) == null;
    }