【Mybatis】(六)分页

分页

1.为什么要分页?

• 减少数据的处理量

2.使用Limit分页

• 语法

  SELECT * FROM user LIMIT startIndex,pageSize; #起始下标从0开始
  SELECT * FROM user limit n; #[0,n]
  

  
  

3.使用mybatis实现分页

• 接口

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

• UserMapper.xml

  <resultMap id="UserMap" type="pojo.User">
          <result column="pwd" property="password" />
  </resultMap>
   <!--分页-->
  <select id="getUserByLimit" parameterType="map" resultMap="UserMap">
          select * from mybatiss.user limit #{startIndex},#{pageSize};
  </select>
  

• 测试

   @Test
      public void getUserByLimit(){
          SqlSession sqlSession = MybatisUtils.getSqlSession();
          UserMapper mapper = sqlSession.getMapper(UserMapper.class);
          Map<String, Integer> map = new 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();
      }
  

4.使用RowBounds实现分页（一般不用了）

​ 不再使用SQL实现分页

• 接口

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

• UserMapper.xml

   <select id="getUserByRowBounds" resultMap="UserMap">
          select * from mybatiss.user;
  </select>
  

• 测试

   @Test
      public void getUserByRowBounds(){
          SqlSession sqlSession = MybatisUtils.getSqlSession();
  
          RowBounds rowBounds = new RowBounds(0, 2);
  
          //通过java代码层面实现分页
          List<User> userList=sqlSession.selectList("dao.UserMapper.getUserByRowBounds",null,rowBounds);
  
          for (User user : userList) {
              System.out.println(user);
          }
  
          sqlSession.close();
      }
  

5.分页插件PageHelper