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 * form user limit startIndex,pageSize;
SELECT * from user limit 3;  #[0,n]

使用Mybatis实现分页，核心SQL

• 接口

//分页查询
    List<User> getUserByLimit(Map<String,Integer> map);
}

• Mapper.xml

<!--分页查询-->
    <select id="getUserByLimit" parameterType="map" resultMap="UserMap">
        select * from mybatis.user limit #{startIndex},#{pageSize}
    </select>

• 测试

@Test
    public void getUserByLimit(){
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);

        HashMap<String, Integer> map = new HashMap<String, Integer>();
        //需要一个map，故new一个Hashmap
        map.put("startIndex",0);
        map.put("pageSize",2);
        List<User> userList = mapper.getUserByLimit(map);
        for (User user : userList) {
            System.out.println(user);
        }
        sqlSession.close();
    }

7.2RowBounds分页【不建议开发中使用】

不再使用SQL实现分页

1.接口

//使用RowBounds实现分页
    List<User> getUserByRowBounds();

2.Mapper.xml

<!--分页查询RowBounds-->
    <select id="getUserByRowBounds" resultMap="UserMap">
        select * from mybatis.user
    </select>

3.测试

@Test
    public void getUserByRowBounds(){
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        //RowBounds实现
        RowBounds rowBounds = new RowBounds(1,2);
        //通过Java代码实现分页
        List<User> userList = sqlSession.selectList("com.itxiaofei.dao.UserMapper.getUserByRowBounds", null, rowBounds);
        for (User user : userList) {
            System.out.println(user);
        }
        sqlSession.close();
    }

7.3分页插件

了解即可，万一以后公司的架构师，要求使用，要知道这是什么东西！