Spring Data JPA分页查询

使用Spring Data JPA的朋友，在实际工作中经常需要用到分页查询。下面介绍一个简单的分页查询的例子：查询学生信息，每页10行数据，并按成绩排序。先看数据表：

 

实现：repo需要继承PagingAndSortingRepository，如下：

public interface StudentRepo extends CrudRepository,         JpaSpecificationExecutor,
        PagingAndSortingRepository {
}

需要用到PageRequest，我们来看一下PageRequest（为方便查看，本人去掉了部分内容，并增加了注释）：

public class PageRequest extends AbstractPageRequest {

	private static final long serialVersionUID = -4541509938956089562L;

	private final Sort sort;

	//简单的，指定页码和每页行数
	public PageRequest(int page, int size) {
		this(page, size, null);
	}

	//指定页码、每页行数、排序
	public PageRequest(int page, int size, Direction direction, String... properties) {
		this(page, size, new Sort(direction, properties));
	}

	//指定页码、每页行数、排序
	public PageRequest(int page, int size, Sort sort) {
		super(page, size);
		this.sort = sort;
	}

	//下一页
	public Pageable next() {
		return new PageRequest(getPageNumber() + 1, getPageSize(), getSort());
	}

	//上一页
	public PageRequest previous() {
		return getPageNumber() == 0 ? this : new PageRequest(getPageNumber() - 1, getPageSize(), getSort());
	}

	//第一页
	public Pageable first() {
		return new PageRequest(0, getPageSize(), getSort());
	}
}

 我们发现，PageRequest提供了很多构造方法，根据实际情况灵活选择。下面看实现代码：

    public void queryStudentByPage() {
        //按分数倒序排列
        Sort sort = new Sort(Sort.Direction.DESC,"score");
        //构造PageRequest分页条件，第一页、每页10行、排序条件
        PageRequest pageRequest = new PageRequest(0,10, sort);
        Page page = studentRepo.findAll(pageRequest);
        List studentEntities = page.getContent();
        for (StudentEntity studentEntity : studentEntities) {
            System.out.println(studentEntity.toString());
        }
    }

查询结果如下：

Hibernate: 
    select
        studentent0_.id as id1_0_,
        studentent0_.address as address2_0_,
        studentent0_.birthday as birthday3_0_,
        studentent0_.name as name4_0_,
        studentent0_.school as school5_0_,
        studentent0_.score as score6_0_,
        studentent0_.tel as tel7_0_ 
    from
        t_student studentent0_ 
    order by
        studentent0_.score desc limit ?
Hibernate: 
    select
        count(studentent0_.id) as col_0_0_ 
    from
        t_student studentent0_

StudentEntity{id='6c09a952f5b9474fb56996db642e7bab', name='沙鸿飞', address='玉龙小区', tel='12314512312311', school='青大附中', birthday='2001-03-01', score=99}
StudentEntity{id='c46800036ea94caea07c1f2b90576c2f', name='赵继峰', address='菜市场', tel='12314512312311', school='大庆中学', birthday='2002-03-11', score=99}
StudentEntity{id='6b2bc83ff6ea4f7aa95986e3eeb1883f', name='赵六', address='玉龙小区', tel='12314512312311', school='青大附中', birthday='2001-03-01', score=98}
StudentEntity{id='76a5fad795aa4605b43daf9c5f4e8edd', name='张逸杰', address='菜市场', tel='12314512312311', school='胜利中学', birthday='2002-03-11', score=98}
StudentEntity{id='81fbeb9e7e8749e78c2495e169766274', name='吕春芳', address='柏景湾', tel='12314512312311', school='实验中学', birthday='2000-03-11', score=98}
StudentEntity{id='b6ef1f42e8a64367abc251af22246870', name='郎芬', address='菜市场', tel='12314512312311', school='西城中学', birthday='2001-03-11', score=98}
StudentEntity{id='bc56bad3fd4e4604abe8a1c4ee2c1f66', name='李海峰', address='菜市场', tel='12314512312311', school='明湖中学', birthday='2002-02-11', score=98}
StudentEntity{id='ded2215cfbb846d296aece2531bce6b8', name='赵九', address='岩石寨', tel='12314512312311', school='中山一小', birthday='2001-01-01', score=98}
StudentEntity{id='e838a9fbbd4240d5a0922d1112b2171d', name='钱十', address='南淮安', tel='12314512312311', school='西城中学', birthday='2001-03-31', score=98}
StudentEntity{id='babee95b37c04db38c0e74d923521ec5', name='钱十', address='南淮安', tel='12314512312311', school='山大附中', birthday='2001-03-11', score=89}

通过控制台打印出的sql我们发现里面通过limit限定返回从第几行到第几行的数据，另外发现不光查询了前10行的数据，还统计了总条数。那是因为返回的结果Page提供getTotalPages（获取总页数）、getTotalElements（获取总行数）等方法，需要在查询的时候获取总的数据行数。