Mybatis

7、分页

思考：为什么要分页？

减少数据的处理量

7.1、使用Limit分页

语法：SELECT * FROM user LIMIT startIndex,pageSize;
SELECT * FROM user LIMIT 3;  #[0,n]

使用Mybatis实现分页，核心SQL

接口

//    分页
List<User>getUserByLimit(Map<String,Object>map);

Mapper.xml

<!--    分页实现查询-->
<select id="getUserByLimit" parameterType="map" resultType="user">
select *
from user limit #{startIndex},#{pageSize};
</select>

测试

推断：起始位置 = （当前页面 - 1 ） * 页面大小

@Test
public void getUserByLimit(){
    SqlSession sqlSession = MybatisUtil.getSqlSession();
    UserMapper mapper = sqlSession.getMapper(UserMapper.class);
    int currentPage = 1;  //第几页
    int pageSize = 2;  //每页显示几个
    HashMap<String, Object> map = new HashMap<>();
    map.put("startIndex",(currentPage-1)*pageSize);
    map.put("pageSize",pageSize);
    List<User> userByLimit = mapper.getUserByLimit(map);
    for (User user : userByLimit) {
        System.out.println(user);
    }
    sqlSession.close();
}

7.2、RowBounds分页

不在使用SQL实现分页

接口

//    分页2
List<User>getUserByRowBounds();

mapper.xml

<select id="getUserByRowBounds" resultType="user">
    select *
    from user;
</select>

测试

    @Test
    public void getUserByRowBounds(){
        SqlSession sqlSession = MybatisUtil.getSqlSession();

//        RowBounds 实现
        RowBounds rowBounds = new RowBounds(0, 2);

//        通过Jav代码层面实现分页
        List<User> userList = sqlSession.selectList("getUserByRowBounds",null,rowBounds);
        for (User user : userList) {
            System.out.println(user);
        }
        sqlSession.close();
    }