使用Java流的具有相同ID /名称的对象的组列表

Question

我有一个类似于List的Student类的对象列表。学生班级上有日期和另一个班级对象的排序图见下文：

class Student{
    String name;
    SortedMap<LocalDate, Score> semScore = new TreeMap()<>; 
}

class Score{
   int score;
   String grade;
}

我如何汇总学生列表，以按学生姓名将所有排序的地图合并到单个地图组中。对于例如

Score score = new Score(90, "A");
SortedMap<LocalDate, Score> sMap = new TreeMap<>();
sMap.put(LocalDate.now(), score);

Student s = new Student("Bob", sMap);

So multiple records are in the list for a Student with a given name with one map of score.
I need to aggregate all the scores into the same student object like group by name.

How can we do it using java streams?

Thanks

Answer 1

由于必须合并它们，所以Collectors#toMap包含合并功能：

Map<String, Student> mergedStudents = list.stream().collect(Collectors.toMap(Student::getName, Function.identity(), (s1, s2) -> {
  SortedMap<LocalDate, Score> semScore = new TreeMap<>(s1.getSemScore());
  semScore.putAll(s2.getSemScore());
  return new Student(s1.getName(), semScore);
}));