MongoDB分页的Java实现和分页需求的思考

function printStudents(startValue, nPerPage) {
  let endValue = null;
  db.students.find( { _id: { $lt: startValue } } )
             .sort( { _id: -1 } )
             .limit( nPerPage )
             .forEach( student => {
               print( student.name );
               endValue = student._id;
             } );

  return endValue;
}

function printStudents(startValue, nPerPage) {
  let endValue = null;
  db.students.find( { _id: { $gt: startValue } } )
             .sort( { _id: 1 } )
             .limit( nPerPage )
             .forEach( student => {
               print( student.name );
               endValue = student._id;
             } );

  return endValue;
}

public ObjectId(Date date) {
    this(dateToTimestampSeconds(date), MACHINE_IDENTIFIER, PROCESS_IDENTIFIER, NEXT_COUNTER.getAndIncrement(), false);
}

//org.bson.types.ObjectId#dateToTimestampSeconds 
private static int dateToTimestampSeconds(Date time) {
    return (int)(time.getTime() / 1000L);
}

//java.util.Date#getTime
/**
 * Returns the number of milliseconds since January 1, 1970, 00:00:00 GMT
 * represented by this <tt>Date</tt> object.
 *
 * @return  the number of milliseconds since January 1, 1970, 00:00:00 GMT
 *          represented by this date.
 */
public long getTime() {
    return getTimeImpl();
}

public PageResult<StatByClientRs> findByDurationPage(FindByDurationPageRq rq) {
    final Criteria criteriaDefinition = Criteria.where("duration").is(rq.getDuration());

    final Query query = new Query(criteriaDefinition).with(new Sort(Lists.newArrayList(new Order(Direction.ASC, "_id"))));

    //分页逻辑
    long total = mongoTemplate.count(query, StatByClient.class);
    Integer pageSize = rq.getPageSize();
    Integer pageNum = rq.getPageNum();
    String lastId = rq.getLastId();
    final Integer pages = (int) Math.ceil(total / (double) pageSize);
    if (pageNum<=0 || pageNum> pages) {
        pageNum = 1;
    }
   
    if (StringUtils.isNotBlank(lastId)) {
        if (pageNum != 1) {
            criteriaDefinition.and("_id").gt(new ObjectId(lastId));
        }
        query.limit(pageSize);
    } else {
        int skip = pageSize * (pageNum - 1);
        query.skip(skip).limit(pageSize);
    }
    List<StatByClient> statByClientList = mongoTemplate.find(query, StatByClient.class);

    PageResult<StatByClientRs> pageResult = new PageResult<>();
    pageResult.setTotal(total);
    pageResult.setPages(pages);
    pageResult.setPageSize(pageSize);
    pageResult.setPageNum(pageNum);
    pageResult.setList(mapper.mapToListRs(statByClientList));
    return pageResult;
}

import com.google.common.collect.Lists;
import com.shuwei.d2.message.PageResult;
import java.util.List;
import java.util.function.Function;
import java.util.stream.Collectors;
import org.apache.commons.lang3.StringUtils;
import org.bson.types.ObjectId;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.domain.Sort;
import org.springframework.data.domain.Sort.Direction;
import org.springframework.data.domain.Sort.Order;
import org.springframework.data.mongodb.core.MongoTemplate;
import org.springframework.data.mongodb.core.query.Criteria;
import org.springframework.data.mongodb.core.query.Query;
import org.springframework.stereotype.Component;

/**
 * MongoDB分页查询工具类.
 *
 * @author Ryan Miao at 2018-06-07 14:46
 **/
@Component
public class MongoPageHelper {

    public static final int FIRST_PAGE_NUM = 1;
    public static final String ID = "_id";
    private final MongoTemplate mongoTemplate;

    @Autowired
    public MongoPageHelper(MongoTemplate mongoTemplate) {
        this.mongoTemplate = mongoTemplate;
    }


    /**
     * 分页查询，直接返回集合类型的结果.
     *
     * @see MongoPageHelper#pageQuery(org.springframework.data.mongodb.core.query.Query,
     * java.lang.Class, java.util.function.Function, java.lang.Integer, java.lang.Integer,
     * java.lang.String)
     */
    public <T> PageResult<T> pageQuery(Query query, Class<T> entityClass, Integer pageSize,
        Integer pageNum) {
        return pageQuery(query, entityClass, Function.identity(), pageSize, pageNum, null);
    }

    /**
     * 分页查询，不考虑条件分页，直接使用skip-limit来分页.
     *
     * @see MongoPageHelper#pageQuery(org.springframework.data.mongodb.core.query.Query,
     * java.lang.Class, java.util.function.Function, java.lang.Integer, java.lang.Integer,
     * java.lang.String)
     */
    public <T, R> PageResult<R> pageQuery(Query query, Class<T> entityClass, Function<T, R> mapper,
        Integer pageSize, Integer pageNum) {
        return pageQuery(query, entityClass, mapper, pageSize, pageNum, null);
    }

    /**
     * 分页查询.
     *
     * @param query Mongo Query对象，构造你自己的查询条件.
     * @param entityClass Mongo collection定义的entity class，用来确定查询哪个集合.
     * @param mapper 映射器，你从db查出来的list的元素类型是entityClass, 如果你想要转换成另一个对象，比如去掉敏感字段等，可以使用mapper来决定如何转换.
     * @param pageSize 分页的大小.
     * @param pageNum 当前页.
     * @param lastId 条件分页参数, 区别于skip-limit，采用find(_id>lastId).limit分页.
     * 如果不跳页，像朋友圈，微博这样下拉刷新的分页需求，需要传递上一页的最后一条记录的ObjectId。 如果是null，则返回pageNum那一页.
     * @param <T> collection定义的class类型.
     * @param <R> 最终返回时，展现给页面时的一条记录的类型。
     * @return PageResult，一个封装page信息的对象.
     */
    public <T, R> PageResult<R> pageQuery(Query query, Class<T> entityClass, Function<T, R> mapper,
        Integer pageSize, Integer pageNum, String lastId) {
        //分页逻辑
        long total = mongoTemplate.count(query, entityClass);
        final Integer pages = (int) Math.ceil(total / (double) pageSize);
        if (pageNum <= 0 || pageNum > pages) {
            pageNum = FIRST_PAGE_NUM;
        }
        final Criteria criteria = new Criteria();
        if (StringUtils.isNotBlank(lastId)) {
            if (pageNum != FIRST_PAGE_NUM) {
                criteria.and(ID).gt(new ObjectId(lastId));
            }
            query.limit(pageSize);
        } else {
            int skip = pageSize * (pageNum - 1);
            query.skip(skip).limit(pageSize);
        }

        final List<T> entityList = mongoTemplate
            .find(query.addCriteria(criteria)
                    .with(new Sort(Lists.newArrayList(new Order(Direction.ASC, ID)))),
                entityClass);

        final PageResult<R> pageResult = new PageResult<>();
        pageResult.setTotal(total);
        pageResult.setPages(pages);
        pageResult.setPageSize(pageSize);
        pageResult.setPageNum(pageNum);
        pageResult.setList(entityList.stream().map(mapper).collect(Collectors.toList()));
        return pageResult;
    }

}

import com.fasterxml.jackson.annotation.JsonInclude;
import com.fasterxml.jackson.annotation.JsonInclude.Include;
import io.swagger.annotations.ApiModelProperty;
import java.util.List;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

/**
 * 分页结果.
 * @author Ryan
 */
@Data
@AllArgsConstructor
@NoArgsConstructor
@JsonInclude(Include.NON_NULL)
public class PageResult<T> {

    @ApiModelProperty("页码，从1开始")
    private Integer pageNum;

    @ApiModelProperty("页面大小")
    private Integer pageSize;

    @ApiModelProperty("总数")
    private Long total;

    @ApiModelProperty("总页数")
    private Integer pages;

    @ApiModelProperty("数据")
    private List<T> list;

}

public PageResult<StatByClientRs> findByDurationPage(FindByDurationPageRq rq) {
    final Query query = new Query(Criteria.where("duration").is(rq.getDuration()));

    return mongoPageHelper.pageQuery(query, StatByClient.class, mapper::mapToRs, rq.getPageSize(),
        rq.getPageNum(), rq.getLastId());
}

<repositories>
    <repository>
        <id>jitpack.io</id>
        <url>https://jitpack.io</url>
    </repository>
</repositories>

<dependency>
    <groupId>com.github.Ryan-Miao</groupId>
    <artifactId>mongo-page-helper</artifactId>
    <version>1.0</version>
</dependency>

@Configuration
public class MongoConfiguration{

    @Autowired
    private MongoTemplate mongoTemplate;
    @Bean
    public MongoPageHelper mongoPageHelper() {
        return new MongoPageHelper(mongoTemplate);
    }

}