Java中分页查询MongoDB数据

　　在Java中操作MongoDB时会遇到分页查询数据的情况，此时我们可以按如下步骤来实现：

　　1、创建一个分页类

import org.springframework.data.domain.PageRequest;
import org.springframework.data.domain.Pageable;
import org.springframework.data.domain.Sort;

public class MongoDbPageable implements Pageable {
    /**分页码*/
    private int pageNumber = 1;
    /**每页大小*/
    private int pageSize = 10;
    /**排序*/
    private Sort sort;

    @Override
    public int getPageNumber() {
        return pageNumber;
    }

    public void setCurrentPage(int pageNumber) {
        this.pageNumber = pageNumber;
    }

    @Override
    public int getPageSize() {
        return pageSize;
    }

    public void setPageSize(int pageSize) {
        this.pageSize = pageSize;
    }

    @Override
    public Sort getSort() {
        return sort;
    }

    public void setSort(Sort sort) {
        this.sort = sort;
    }

    @Override
    public long getOffset() {
        return (pageNumber - 1) * pageSize;
    }

    @Override
    public Pageable first() {
        return PageRequest.of(0, pageSize, sort);
    }

    @Override
    public boolean hasPrevious() {
        return false;
    }

    @Override
    public Pageable next() {
        return PageRequest.of(pageNumber + 1, pageSize, sort);
    }

    @Override
    public Pageable previousOrFirst() {
        return pageNumber == 0 ? this : PageRequest.of(pageNumber - 1, pageSize, sort);
    }
}

　　2、分页类的实践

private List<Object> find(int pageNumber, int pageSize,  Sort.Direction direction){
         MongoDbPageable pageable = new MongoDbPageable();
         pageable.setCurrentPage(pageNumber);
         pageable.setPageSize(pageSize);
         // direction: Sort.Direction.DESC或者Sort.Direction.ASC
         Sort sort = new Sort(direction, "_id");
         pageable.setSort(sort);
         Query query = new Query();
         query.with(pageable);
         return mongoTemplate.find(query, Object.class, collectionName);
     }

　　说明：分页类具有排序的功能，实践中是按照ObjectId(_id)进行降序排列的。