java 集合分组，集合根据某一条件分组，封装成map形式

原创

qq593b783858edc 2022-11-29 11:05:45 ©著作权

文章标签 java 集合分组 list 构造方法实体类 文章分类 云平台云计算

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集合中为对象，根据对象中的某一属性值分组

例子

1、实体类：构造方法、get/set方法、toString方法省略

public class User {
    private String id;
    
    private String name;
    
    private String age;
    
    .......
    .......
}

2、测试类：

public static void main(String[] args){
    List<User> list = new ArrayList<>();
    User user1 = new User("1", "张三", "10");
    User user2 = new User("2", "张三", "11");
    User user3 = new User("2", "张三", "12");
    User user4 = new User("4", "李四", "13");
    User user5 = new User("5", "李四", "14");
    User user6 = new User("6", "李四", "15");
    User user7 = new User("7", "王五", "16");
    User user8 = new User("8", "王五", "17");
    User user9 = new User("9", "王五", "18");
    list.add(user1);
    list.add(user2);
    list.add(user3);
    list.add(user4);
    list.add(user5);
    list.add(user6);
    list.add(user7);
    list.add(user8);
    list.add(user9);
    Map<String,List<User>> userGroupMap = list.stream().
        collect(Collectors.groupingBy(User::getName));
    Set<String> keySet = userGroupMap.keySet();
    keySet.forEach((key)->{
      System.out.println(key);
      userGroupMap.get(key).forEach((user)->System.out.println(user));
    });
  }

结果为：

李四
User [id=4, name=李四, age=13]
User [id=5, name=李四, age=14]
User [id=6, name=李四, age=15]
张三
User [id=1, name=张三, age=10]
User [id=2, name=张三, age=11]
User [id=2, name=张三, age=12]
王五
User [id=7, name=王五, age=16]
User [id=8, name=王五, age=17]
User [id=9, name=王五, age=18]

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