mybatis開發dao的方式

mybatis基於傳統dao的開發方式

第一步：開發接口

public interface UserDao {
    public User getUserById(int id) throws Exception;
    public void insertUser(User user) throws Exception;
}

第二步：設置實現類

public class UserDaoImpl implements UserDao {
    private SqlSessionFactory sqlSessionFactory;
    public UserDaoImpl(SqlSessionFactory sqlSessionFactory) {
        this.sqlSessionFactory = sqlSessionFactory;
    }
    public UserDaoImpl() {
        super();
    }
    @Override
    public User getUserById(int id) throws Exception {
        //獲取sqlSession,需要使用sqlSessionFactory
        SqlSession session = sqlSessionFactory.openSession();
        try {
            User user = session.selectOne("selectUserById", id);
            return user;
        } finally{
            session.close();
        }
    }
    @Override
    public void insertUser(User user) throws Exception {
        //獲取sqlSession,需要使用sqlSessionFactory
        SqlSession session = sqlSessionFactory.openSession();
        try {
            session.insert("insertUser", user);
            session.commit();
        } finally{
            session.close();
        }
    }
}

第三步：設置對應的mapper文件

<?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">
<mapper namespace="mybatis.mapper.UserMapper">
    <!-- 根據id獲取用戶信息 -->
    <select id="selectUserById" parameterType="int" resultType="user">
        select * from user where id = #{id}
    </select>

    <!-- 向數據庫插入一條數據 -->
    <insert id="insertUser" parameterType="user">
    <selectKey keyProperty="id" resultType="int" order="AFTER">
        select last_insert_id();
    </selectKey>
        insert into user(username,birthday,sex,address) 
            values(#{username},#{birthday},#{sex},#{address})
    </insert>

</mapper>

加載mapper文件

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE configuration
  PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
  "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>

    <!-- 加載外部配置文件 -->
    <properties resource="db.properties">
    </properties>


    <!-- 這個environments定義了我們的數據庫的連接操作 -->
      <environments default="development">
        <environment id="development">
          <transactionManager type="JDBC"/>
          <dataSource type="POOLED">
            <property name="driver" value="${driver}"/>
            <property name="url" value="${url}"/>
            <property name="username" value="${username}"/>
            <property name="password" value="${password}"/>
          </dataSource>
        </environment>
      </environments>
      <!-- 通過mappers來指定加載我們對應的mapper文件 -->
        <mappers>
            <mapper resource="UserMapper.xml"/> 
        </mappers>
</configuration>

第五步：編寫測試案例

public class UserDaoTest {

    private SqlSessionFactory getSqlSessionFactory() throws IOException {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        return sqlSessionFactory;
    }

    @Test
    public void testGetUserById() throws Exception {
        SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();
        UserDao userDao = new UserDaoImpl(sqlSessionFactory);
        User user = userDao.getUserById(1);
        System.out.println(user);
    }

    @Test
    public void testInsertUser() throws Exception {
        SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();
        UserDao userDao = new UserDaoImpl(sqlSessionFactory);
        User user = new User();
        user.setUsername("安茱莉");
        user.setSex("0");
        user.setAddress("好萊塢38號");
        userDao.insertUser(user);
    }
}

存在的問題

• Dao方法體存在重複代碼：通過SqlSessionFactory創建SqlSession，調用SqlSession的數據庫操作方法
• 調用sqlSession的數據庫操作方法需要指定statement的id，這裏存在硬編碼，不得於開發維護。

---

---

通過接口代理的方式來開發dao

官方重點推薦這種方式

開發規範：

Mapper接口開發方法只需要編寫Mapper接口（相當於Dao接口），由Mybatis框架根據接口定義創建接口的動態代理對象，代理對象的方法體同上邊Dao接口實現類方法。

Mapper接口開發需要遵循以下規範：

1、 Mapper.xml文件中的namespace與mapper接口的類路徑相同。
2、 Mapper接口方法名和Mapper.xml中定義的每個statement的id相同
3、 Mapper接口方法的輸入參數類型和mapper.xml中定義的每個sql 的parameterType的類型相同
4、 Mapper接口方法的輸出參數類型和mapper.xml中定義的每個sql的resultType的類型相同

第一步：定義接口

public interface UserMapper {
        // 根據id查找用戶
        public User findUserById(int id) throws Exception;

        // 插入用戶信息
        public void insertUser(User user) throws Exception;
}

第二步：定義mapper文件

<?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">
<mapper namespace="mybatis.mapper.UserMapper">
    <!-- 根據id獲取用戶信息 -->
    <select id="findUserById" parameterType="int" resultType="user">
        select * from user where id = #{id}
    </select>

    <!-- 向數據庫插入一條數據 -->
    <insert id="insertUser" parameterType="user">
        insert into user(username,birthday,sex,address) 
            values(#{username},#{birthday},#{sex},#{address})
    </insert>
</mapper>

第三步：加載mapper文件

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE configuration
  PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
  "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>

    <!-- 別名的配置 -->
    <typeAliases>
        <!-- 不區分大小寫的 -->
        <!-- <typeAlias type="domain.User" alias="user"/> -->
        <!-- 掃描這個包下面的所有類，起別名，也是不區分大小寫的 ,名字是類名不帶包，推薦這種方式-->
        <package name="domain"/>
    </typeAliases>

    <!-- 加載外部配置文件 -->
    <properties resource="db.properties">
    </properties>

    <!-- 這個environments定義了我們的數據庫的連接操作 -->
      <environments default="development">
        <environment id="development">
          <transactionManager type="JDBC"/>
          <dataSource type="POOLED">
            <property name="driver" value="${driver}"/>
            <property name="url" value="${url}"/>
            <property name="username" value="${username}"/>
            <property name="password" value="${password}"/>
          </dataSource>
        </environment>
      </environments>

        <!-- 通過mappers來指定加載我們對應的mapper文件 -->
        <!-- 此種方法要求mapper接口名稱和mapper映射文件名稱相同，且放在同一個目錄中。 -->
          <mappers>
            <mapper resource="mapper.xml"/>
    <!--    <mapper class="mybatis.mapper.UserMapper"/> -->
    <!-- 加載包下所有mapper接口，要求接口名稱和mapper映射文件名稱相同，且放在同一個目錄中。 -->
            <package name="mybatis.mapper"/>
          </mappers>
</configuration>

第四步：開發測試代碼

public class UserMapperTest {

    /**
     * 通過接口代理開發dao層的測試
     * 調用getUserById方法，傳遞id參數
     * 輸出user對象到控制檯
     */
    @Test
    public void findUserByIdTest() throws Exception{
        SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();
        SqlSession sqlSession = sqlSessionFactory.openSession(true);
        //mybatis會產生一個代理對象
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);

        User user = mapper.getUserById(2);
        System.out.println(user);
        sqlSession.close();
    }

    ...

    /**
     * 抽取方法，保證項目中SQLSessionFactory的單例
     */
    private SqlSessionFactory getSqlSessionFactory() throws IOException {
        InputStream inputStream = Resources.getResourceAsStream("sqlMapConfig.xml");
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        return sqlSessionFactory;
    }
}

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補充：mybatis默認支持的別名：

別名	映射的類型
_byte	byte
_long	long
_short	short
_int	int
_integer	int
_double	double
_float	float
_boolean	boolean
string	String
byte	Byte
long	Long
short	Short
int	Integer
integer	Integer
double	Double
float	Float
boolean	Boolean
date	Date
decimal	BigDecimal
bigdecimal	BigDecimal
map	Map