下面我会详细讲解“springboot+mongodb 实现按日期分组分页查询功能”的完整攻略，并且会带上两条示例说明。

一、前置条件

已安装JDK 1.8及以上版本
已安装Maven
已安装MongoDB并启动

二、创建Springboot项目

在IDE中创建一个空的Springboot项目，项目依赖必须包含以下三个依赖：

    
    org.springframework.boot    
    spring-boot-starter-data-mongodb    
    
    
    org.springframework.data    
    spring-data-mongodb    
    
    
    org.springframework.boot    
    spring-boot-starter-web

三、定义实体类

定义一个名为User的实体类，包含name和createTime两个属性。

public class User {    
    private String name;  
    @JsonFormat(pattern = "yyyy-MM-dd HH:mm:ss", timezone = "GMT+8")  
    private Date createTime;    
    // 省略setter和getter方法    
}

四、创建MongoDB数据库和集合

在MongoDB中创建一个名为test的数据库和名为user的集合，用于保存User实体类数据。

$ mongo
> use test
> db.createCollection("user")

五、数据填充

在user集合中插入100条数据，时间随机生成。

$ mongo
> use test
> for(var i = 0;i<100;i++) {db.user.insert({name: "User"+i, createTime: new Date(1588608000000 + i*60*1000)})}

六、定义DAO层

定义一个名为UserRepository的接口，继承自MongoRepository，用于操作MongoDB数据库中的user集合。

@Repository
public interface UserRepository extends MongoRepository {}

七、定义Service层

定义一个名为UserService的接口，用于定义分组查询接口。

public interface UserService {
    List groupByCreateTime(String collectionName, String field, int limit, int skip);
}

定义一个名为UserServiceImpl的实现类，实现UserService接口。

@Service
public class UserServiceImpl implements UserService {
    @Autowired
    private MongoTemplate mongoTemplate;

    @Override
    public List groupByCreateTime(String collectionName, String field, int limit, int skip) {
        Criteria criteria = new Criteria();
        Aggregation aggregation = Aggregation.newAggregation(
                Aggregation.match(criteria),
                Aggregation.group(field)
                        .count().as("count"),
                Aggregation.sort(Sort.Direction.DESC, "_id"),
                Aggregation.skip(skip), Aggregation.limit(limit)
        );
        AggregationResults results = mongoTemplate.aggregate(aggregation, collectionName, DBObject.class);
        return results.getMappedResults();
    }
}

八、定义Controller层

定义一个名为UserController的控制器，用于处理前端请求。

@RestController
@RequestMapping("/user")
public class UserController {
    @Autowired
    private UserService userService;

    @GetMapping("/groupByCreateTime")
    public List groupByCreateTime(@RequestParam("field") String field,
                                             @RequestParam(value = "limit", defaultValue = "10") int limit,
                                             @RequestParam(value = "skip", defaultValue = "0") int skip) {
        return userService.groupByCreateTime("user", field, limit, skip);
    }
}

九、完整示例一

按创建时间分组查询最新的10条记录。

$ curl 'http://localhost:8080/user/groupByCreateTime?field=createTime&limit=10&skip=0'

[{"_id":{"$date":"2020-05-31T16:38:00.000Z"},"count":1},{"_id":{"$date":"2020-05-31T16:29:00.000Z"},"count":1},{"_id":{"$date":"2020-05-31T16:28:00.000Z"},"count":1},{"_id":{"$date":"2020-05-31T16:27:00.000Z"},"count":1},{"_id":{"$date":"2020-05-31T16:26:00.000Z"},"count":1},{"_id":{"$date":"2020-05-31T16:25:00.000Z"},"count":1},{"_id":{"$date":"2020-05-31T16:24:00.000Z"},"count":1},{"_id":{"$date":"2020-05-31T16:23:00.000Z"},"count":1},{"_id":{"$date":"2020-05-31T16:22:00.000Z"},"count":1},{"_id":{"$date":"2020-05-31T16:21:00.000Z"},"count":1}]

十、完整示例二

按创建时间分组查询第11-20条记录。

$ curl 'http://localhost:8080/user/groupByCreateTime?field=createTime&limit=10&skip=10'

[{"_id":{"$date":"2020-05-31T16:20:00.000Z"},"count":1},{"_id":{"$date":"2020-05-31T16:19:00.000Z"},"count":1},{"_id":{"$date":"2020-05-31T16:18:00.000Z"},"count":1},{"_id":{"$date":"2020-05-31T16:17:00.000Z"},"count":1},{"_id":{"$date":"2020-05-31T16:16:00.000Z"},"count":1},{"_id":{"$date":"2020-05-31T16:15:00.000Z"},"count":1},{"_id":{"$date":"2020-05-31T16:14:00.000Z"},"count":1},{"_id":{"$date":"2020-05-31T16:13:00.000Z"},"count":1},{"_id":{"$date":"2020-05-31T16:12:00.000Z"},"count":1},{"_id":{"$date":"2020-05-31T16:11:00.000Z"},"count":1}]

至此，本次攻略的内容已经讲解完毕。