List集合分组求和

List集合分组求和

适用场景

[{"name":"zhangsan", "grade":90}, {"name":"lisi", "grade":100}, {"name":"zhangsan", "grade":95}]

=>

[{"name":"zhangsan", "grade":185}, {"name":"lisi", "grade":100}]

代码示例

// [{"name":"zhangsan", "grade":90}, {"name":"lisi", "grade":100}, {"name":"zhangsan", "grade":95}]
List<User> userList = new ArrayList<>();
Map<String, User> mergedUsers = userList.stream()
                .collect(Collectors.toMap(
                        User::getName,
                        Function.identity(),
                        (existing, replacement) ->
                        {
                            existing.setGrade(existing.getGrade() + replacement.getGrade());
                            return existing;
                        },
                        LinkedHashMap::new // 保持插入顺序
                ));
// [{"name":"zhangsan", "grade":185}, {"name":"lisi", "grade":100}]
Collection<User> values = mergedUsers.values();