分页

一、为什么要分页

减少数据的处理量

二、limit分页

# startIndex, pageSize
select * from mybatis.user limit 0, 1

//User实体类
public class User {
    int id;
    String name;
    String pwd;

    public User() {}

    public User(int id, String name, String pwd) {
        this.id = id;
        this.name = name;
        this.pwd = pwd;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getPwd() {
        return pwd;
    }

    public void setPwd(String pwd) {
        this.pwd = pwd;
    }

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", pwd='" + pwd + '\'' +
                '}';
    }
}

limit分页实现

//UserMapper接口
public interface UserMapper {
    //limit分页
    List<User> getUserByLimit(Map<String, Object> map);
}

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<!-- namespace=绑定一个对应的Dao/Mapper接口 -->
<!-- 等同于JDBC中的UserDaoImpl(接口实现类)，转变为Mapper配置文件 -->
<mapper namespace="com.comprehensive.dao.UserMapper">
    <!-- limit分页 -->
    <select id="getUserByLimit" parameterType="map" resultType="com.comprehensive.pojo.User">
        select * from mybatis.user limit #{startIndex}, #{pageSize}
    </select>
</mapper>

//测试类
public class UserMapper_Test {
    @Test
    //limit分页
    public void test3() {
        SqlSession sqlSession = MyBatis_Util.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        Map<String,Object> map = new HashMap<String, Object>();
        map.put("startIndex", 0);
        map.put("pageSize", 1);
        for(User user : mapper.getUserByLimit(map)) System.out.println(user);
        sqlSession.close();
    }
}

三、RowBounds分页

public interface UserMapper {
    //RowBounds分页
    List<User> getUserByRowBounds();
}

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<!-- namespace=绑定一个对应的Dao/Mapper接口 -->
<!-- 等同于JDBC中的UserDaoImpl(接口实现类)，转变为Mapper配置文件 -->
<mapper namespace="com.comprehensive.dao.UserMapper">
    <!-- RowBounds分页 -->
    <select id="getUserByRowBounds" resultType="com.comprehensive.pojo.User">
        select * from mybatis.user
    </select>
</mapper>

public class UserMapper_Test {
    @Test
    //RowBounds分页
    public void test4() {
        //该方式是通过Java代码实现
        SqlSession sqlSession = MyBatis_Util.getSqlSession();
        List<User> userList = sqlSession.selectList("com.comprehensive.dao.UserMapper.getUserByRowBounds",
                null, new RowBounds(0, 1));
        for(User user : userList) System.out.println(user);
        sqlSession.close();
    }
}