List集合中的多条数据，根据对象某个字段进行合并

Myth丶恋晨 2023-03-13 13:53 7阅读 0赞

## 创建Student类 ##

@Data
        @AllArgsConstructor
        private static class Student { 
            private Integer id;
            private String name;
            private Integer age;
        }

## 方法一： ##

通过java的map来实现

List<Student> list = new ArrayList<>();
            list.add(new Student(1, "张三", 10));
            list.add(new Student(2, "李四", 20));
            list.add(new Student(1, "张三", 30));
    
            Map<Integer, Student> map = new HashMap<>();
            for (Student student : list) { 
                Integer id = student.getId();
                if (map.containsKey(id)) { 
                    Student s = map.get(id);
                    s.setAge(s.getAge() + student.getAge());
                    map.put(id, s);
                } else { 
                    map.put(id, student);
                }
            }
    
            List<Student> studentList = new ArrayList<>();
            for(Integer temp:map.keySet()){ 
                studentList.add(map.get(temp));
            }
            System.out.println(studentList);
    //[StreamTest.Student(id=1, name=张三, age=40), StreamTest.Student(id=2, name=李四, age=20)]

## 方法二： ##

通过java8来实现

List<Student> list = new ArrayList<>();
            list.add(new Student(1, "张三", 10));
            list.add(new Student(2, "李四", 20));
            list.add(new Student(1, "张三", 30));
    
            List<Student> studentList = new ArrayList<>();
            list.parallelStream().collect(Collectors.groupingBy(Student::getId, Collectors.toList()))
                    .forEach((id, transfer) -> { 
                        transfer.stream().reduce((a, b) -> new Student(a.getId(), a.getName(), a.getAge() + b.getAge())).ifPresent(studentList::add);
                    });
    
            System.out.println(studentList);
    //[StreamTest.Student(id=1, name=张三, age=40), StreamTest.Student(id=2, name=李四, age=20)]