准备工作

  1. 将之前的项目复制一份，改名，然后将对应的pom文件中的

    改成新的项目名称

  1. 将新的项目导入到idea中，直接打开pom文件 一直点下一步即可
    注意：在编写测试方法时，测试类的名字为UserMapperTest，测试方法的方法名为testXxxx，这样取名符合编程规范

  2. 数据库：

    drop database if exists mybatisdemo;
create  database mybatisdemo;
use mybatisdemo;
DROP TABLE IF EXISTS `user`;
CREATE TABLE `user` (
  `id`         int(11) NOT NULL AUTO_INCREMENT,
  `username`  varchar(32) NOT NULL COMMENT '用户名称',
  `birthday`  date DEFAULT NULL COMMENT '生日',
  `sex`       char(1) DEFAULT NULL COMMENT '性别',
  `address`   varchar(256) DEFAULT NULL COMMENT '地址',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=27 DEFAULT CHARSET=utf8;
INSERT INTO `user` VALUES ('1', '张三', '2018-07-10', '1', '北京');
INSERT INTO `user` VALUES ('2', '李四', '2018-07-10', '0', '上海');
INSERT INTO `user` VALUES ('3', '王五', '2018-07-10', '1', '广州');
INSERT INTO `user` VALUES ('4', '王六', '2018-07-10', '1', '深圳');
INSERT INTO `user` VALUES ('5', '王八', '2018-07-10', '1', '上海');

Mybatis 案例

案例1：返回单一实体对象

  • Mapper接口方法

    //     1.返回单一实体对象
     public User selectById(int id);

  • Mapper.xml

    <!--1.返回单一实体对象-->
   <select id="selectById" parameterType="_int" resultMap="baseResultMap">
        select  id, username ,birthday,sex , address from user where id = #{id}
    </select>

  • test方法

    //除了主体部分的代码 之后的案例将会省略
public class MybatisTest {
    UserMapper userMapper = null;
    InputStream inputstream = null;
    SqlSession sqlSession = null;
    @Before
    public void before(){
        try {
            inputstream = Resources.getResourceAsStream("mybatis-config.xml");
            sqlSession = new SqlSessionFactoryBuilder().build(inputstream).openSession();
            userMapper = sqlSession.getMapper(UserMapper.class);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    //     1.返回单一实体对象
    @Test
    public void testSelectById(){
        User user = userMapper.selectById(1);
        System.out.println(user);
    }
//关闭资源
    @After
    public void after(){
        if(sqlSession!=null){
            sqlSession.close();
        }
        if(inputstream!=null){
            try {
                inputstream.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

  • 运行结果

    DEBUG [main] - ==>  Preparing: select id, username ,birthday,sex , address from user where id = ? 
DEBUG [main] - ==> Parameters: 1(Integer)
TRACE [main] - <==    Columns: id, username, birthday, sex, address
TRACE [main] - <==        Row: 1, 张三, 2018-07-10, 1, 北京
DEBUG [main] - <==      Total: 1
User{id=1, username='张三', birthday=Tue Jul 10 00:00:00 CST 2018, sex='1', address='北京'}

案例2：返回集合实体对象

  • Mapper接口方法

    //     2.返回集合实体对象
     public List<User> selectAllUser();

  • Mapper.xml

    <!--2.返回集合实体对象-->
     <select id="selectAllUser"  resultMap="baseResultMap">
        select  id, username ,birthday,sex , address from user
    </select>

  • test方法

    //除了主体部分的代码 之后的案例将会省略
    //     2.返回集合实体对象
    @Test
    public void testSelectAllUser(){
        List<User> users = userMapper.selectAllUser();
        for (User u :
                users) {
            System.out.println(u);
        }
    }

  • 运行结果

    DEBUG [main] - ==>  Preparing: select id, username ,birthday,sex , address from user 
DEBUG [main] - ==> Parameters: 
TRACE [main] - <==    Columns: id, username, birthday, sex, address
TRACE [main] - <==        Row: 1, 张三, 2018-07-10, 1, 北京
TRACE [main] - <==        Row: 2, 李四, 2018-07-10, 0, 上海
TRACE [main] - <==        Row: 3, 王五, 2018-07-10, 1, 广州
TRACE [main] - <==        Row: 4, 王六, 2018-07-10, 1, 深圳
TRACE [main] - <==        Row: 5, 王八, 2018-07-10, 1, 上海
DEBUG [main] - <==      Total: 5
User{id=1, username='张三', birthday=Tue Jul 10 00:00:00 CST 2018, sex='1', address='北京'}
User{id=2, username='李四', birthday=Tue Jul 10 00:00:00 CST 2018, sex='0', address='上海'}
User{id=3, username='王五', birthday=Tue Jul 10 00:00:00 CST 2018, sex='1', address='广州'}
User{id=4, username='王六', birthday=Tue Jul 10 00:00:00 CST 2018, sex='1', address='深圳'}
User{id=5, username='王八', birthday=Tue Jul 10 00:00:00 CST 2018, sex='1', address='上海'}

    以上的两个例子之前有相似的讲解，比较简单

案例3：返回Map形式的集合

  • Mapper接口方法

    //     3.返回Map形式的集合 
//@MapKey确定了与User在Map中绑定的元素对象
    @MapKey("id")
    Map<Integer,User> selectAllMapUser();

  • Mapper.xml

    <!--3.返回Map形式的集合-->
    <select id="selectAllMapUser" resultMap="baseResultMap">
        select  id, username ,birthday,sex , address from user
    </select>

  • test方法
    返回为map的好处就是可以快速索引主键 此时的主键是id
    使用map的优势 如果用list 就得一个一个的遍历 但是如果使用map

    //     3.返回Map形式的集合
    @Test
    public void testSelectAllMapUser(){
        Map<Integer, User> userMap = userMapper.selectAllMapUser();
        //遍历map
        Set<Integer> keys = userMap.keySet();
        for(Integer key:keys){
            System.out.println(key+"-->" + userMap.get(key));
        }
//example
        System.out.println("-----打印id为4的用户----");
        System.out.println("4"+"-->" + userMap.get(4));
        System.out.println("-----------------------");
}

  • 运行结果

    DEBUG [main] - ==>  Preparing: select id, username ,birthday,sex , address from user 
DEBUG [main] - ==> Parameters: 
TRACE [main] - <==    Columns: id, username, birthday, sex, address
TRACE [main] - <==        Row: 1, 张三, 2018-07-10, 1, 北京
TRACE [main] - <==        Row: 2, 李四, 2018-07-10, 0, 上海
TRACE [main] - <==        Row: 3, 王五, 2018-07-10, 1, 广州
TRACE [main] - <==        Row: 4, 王六, 2018-07-10, 1, 深圳
TRACE [main] - <==        Row: 5, 王八, 2018-07-10, 1, 上海
DEBUG [main] - <==      Total: 5
1-->User{id=1, username='张三', birthday=Tue Jul 10 00:00:00 CST 2018, sex='1', address='北京'}
2-->User{id=2, username='李四', birthday=Tue Jul 10 00:00:00 CST 2018, sex='0', address='上海'}
3-->User{id=3, username='王五', birthday=Tue Jul 10 00:00:00 CST 2018, sex='1', address='广州'}
4-->User{id=4, username='王六', birthday=Tue Jul 10 00:00:00 CST 2018, sex='1', address='深圳'}
5-->User{id=5, username='王八', birthday=Tue Jul 10 00:00:00 CST 2018, sex='1', address='上海'}
-----打印id为4的用户----
4-->User{id=4, username='王六', birthday=Tue Jul 10 00:00:00 CST 2018, sex='1', address='深圳'}
-----------------------

案例4 ：返回Map形式的数据行

  • Mapper接口方法
    //     4.返回Map形式的数据行
     List<Map<String,Object>>selectAllMapCol();
  • Mapper.xml
    <!--4.返回Map形式的数据行-->
    <select id="selectAllMapCol" resultType="map">
        select  id, username ,birthday,sex , address from user
    </select>
  • test方法
    //     4.返回Map形式的数据行
    /*原来的3方法，list 返回的是一个User对象
    *现在把每一行 返回为Map形式
    * 在resultType中写map或者HashMap都可以
    *
    */
    @Test
    public void testSelectAllMapCol(){
        List<Map<String, Object>> maps = userMapper.selectAllMapCol();
        for (Map<String, Object> map :
                maps) {
            Set<String> cols = map.keySet();
            for (String col :
                    cols) {
                System.out.print(col+":"+map.get(col)+"\t");
            }
            System.out.println();
        }
    }
  • 运行结果
    DEBUG [main] - ==>  Preparing: select id, username ,birthday,sex , address from user 
DEBUG [main] - ==> Parameters: 
TRACE [main] - <==    Columns: id, username, birthday, sex, address
TRACE [main] - <==        Row: 1, 张三, 2018-07-10, 1, 北京
TRACE [main] - <==        Row: 2, 李四, 2018-07-10, 0, 上海
TRACE [main] - <==        Row: 3, 王五, 2018-07-10, 1, 广州
TRACE [main] - <==        Row: 4, 王六, 2018-07-10, 1, 深圳
TRACE [main] - <==        Row: 5, 王八, 2018-07-10, 1, 上海
DEBUG [main] - <==      Total: 5
birthday:2018-07-10	address:北京	sex:1	id:1	username:张三	
birthday:2018-07-10	address:上海	sex:0	id:2	username:李四	
birthday:2018-07-10	address:广州	sex:1	id:3	username:王五	
birthday:2018-07-10	address:深圳	sex:1	id:4	username:王六	
birthday:2018-07-10	address:上海	sex:1	id:5	username:王八