JAVA Stream去重代码写法

　　如果需要对一个list进行去重，最简单的写法是

List<DocumentSearch> objects = new ArrayList<>();
        objects.addAll(documentSearchList);
//      objects.addAll(documentSearchTagsList);

        return objects.stream().distinct().collect(Collectors.toList());

　　重点就是distinct方法，需要成员实现hashCode和equals方法

　　还有一种更变态的写法

　　

private static <T> Predicate<T> distinctByKey(Function<? super T, ?> keyExtractor) {
    Set<Object> seen = ConcurrentHashMap.newKeySet();
    return t -> seen.add(keyExtractor.apply(t));
}

studentList = studentList.stream().filter(distinctByKey(Student::getName)).collect(Collectors.toList())

 

3 如果是要根据某个属性，进行去重，该属性未必是equals方法中的比较字段

studentList = studentList.stream().collect(
      collectingAndThen(
        toCollection(() -> new TreeSet<>(Comparator.comparing(Student::getName))), ArrayList::new)
    );
    out.print("根据名字去重后 :");
    out.println(objectMapper.writeValueAsString(studentList));
  }