Mybatis基础学习(二)—开发Dao方式

一、原始Dao开发方式

UserDao.java

public interface UserDao{

public User findUserByID(Serializable id);

public List<User> findUsersByName(String name);
}

UserDaoImpl.java

public class UserDaoImpl implements UserDao{

//SqlSessionFactory是单例存在，不应该在具体实例中创建，需要外部依赖注入
private SqlSessionFactory sqlSessionFactory;

public UserDaoImpl(SqlSessionFactory sqlSessionFactory){
this.sqlSessionFactory = sqlSessionFactory;
}

@Override
public User findUserByID(Serializable id){

SqlSession sqlSession = sqlSessionFactory.openSession();
User user = sqlSession.selectOne("test.findUserById",id);
sqlSession.close();
return user;
}

@Override
public List<User> findUsersByName(String name){

SqlSession sqlSession = sqlSessionFactory.openSession();
List<User> list = sqlSession.selectList("test.findUserByName",name);
sqlSession.close();
return list;
}

}

Test.java

public class UserDaoTest{

private SqlSessionFactory sqlSessionFactory;
private UserDao userDao;

{
String resource = "SqlMapConfig.xml";
InputStream is;
try{
is = Resources.getResourceAsStream(resource);
SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
sqlSessionFactory = builder.build(is);
userDao = new UserDaoImpl(sqlSessionFactory);
}catch(IOException e){
e.printStackTrace();
}

}

@Test
public void testFindUserByID(){

User user = userDao.findUserByID(27);
System.out.println(user);
}

@Test
public void testFindUsersByName(){

List<User> list = userDao.findUsersByName("小明");
for(User user : list){
System.out.println(user);
}
}

}

原始dao开发存在一些问题:

(1)存在一定量的模板代码

     比如: 通过SqlSessionFactory创建SqlSession；调用SqlSession的方法操作数据库；关闭Sqlsession。

(2)存在一些硬编码

     调用SqlSession的方法操作数据库时，需要指定statement的id，这里存在了硬编码。

 

二、Mapper代理开发方式

     Mapper代理的开发方式，程序员只需要编写mapper接口(相当于dao接口)即可。Mybatis会自动的为mapper接口生成动态代理实现类。不过要实现mapper代理的开发方式，需要遵循一些开发规范。

(1)mapper接口的全限定名要和mapper映射文件的namespace的值相同。

(2)mapper接口的方法名称要和mapper映射文件中的statement的id相同。

(3)mapper接口的方法参数只能有一个，且类型要和mapper映射文件中statement的parameterType的值保持一致。

(4)mapper接口的返回值类型要和mapper映射文件中statement的resultType值或resultMap中的type值保持一致。

 

Mapper.java

public interface UserMapper{

public User findUserById(int id);

public void saveUser(User user);
}

 

UserMapper.xml

<?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：此时用mapper代理方式，它的值必须等于对应mapper接口的全限定名  -->
<mapper namespace="com.kiwi.mapper.UserMapper">

<!-- 根据ID查询一个用户 -->
<select id="findUserById" parameterType="int" resultType="com.kiwi.domain.User">
SELECT * FROM USER WHERE id = #{id}
</select>

<!-- 根据名字模糊查询 -->
<select id="findUserByName" parameterType="java.lang.String" resultType="com.kiwi.domain.User">
SELECT * FROM USER WHERE username LIKE '%${value}%'
</select>

<!-- 添加一个用户,并返回插入的ID -->
<insert id="saveUser" parameterType="com.kiwi.domain.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>

<!-- 删除一个用户 -->
<delete id="deleteUser" parameterType="int">
DELETE FROM USER WHERE id = #{id}
</delete>

<!-- 修改一个用户 -->
<update id="updateUser" parameterType="com.kiwi.domain.User">
UPDATE USER SET username = #{username},address = #{address} WHERE id = #{id}
</update>

</mapper>

 

SqlMapConfig.xml

<?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>

<!-- 配置mybatis的环境信息，与spring整合之后，该部分将由spring管理 -->
<environments default="development">
<environment id="development">
<!-- 配置JDBC事务控制，由mybatis进行管理 -->
<transactionManager type="JDBC"></transactionManager>
<!-- 配置数据源，采用dbcp连接池 -->
<dataSource type="POOLED">
<property name="driver" value="com.mysql.jdbc.Driver" />
<property name="url" value="jdbc:mysql://localhost:3306/mybatis?useUnicode=true&characterEncoding=utf8" />
<property name="username" value="root" />
<property name="password" value="123456" />
</dataSource>
</environment>
</environments>

<!-- 加载Mapper -->
<mappers>
<mapper resource="mapper/UserMapper.xml"/>
</mappers>

</configuration>

 

Test.java

private SqlSessionFactory sqlSessionFactory;

@Before
public void setUp() throws Exception{
InputStream inputStream = Resources.getResourceAsStream("SqlMapConfig.xml");
sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
}

@Test
public void testFindUserById(){

SqlSession sqlSession = sqlSessionFactory.openSession();

UserMapper mapper = sqlSession.getMapper(UserMapper.class);
User user = mapper.findUserById(26);
System.out.println(user);

sqlSession.close();
}

@Test
public void testSaveUser(){

SqlSession sqlSession = sqlSessionFactory.openSession();

UserMapper mapper = sqlSession.getMapper(UserMapper.class);
User user = new User("WWW","1",new Date(),"北京市海淀区");
mapper.saveUser(user);
System.out.println(user);

sqlSession.commit();
sqlSession.close();
}

}

 

三、全局配置

1.properties

 

2.typeAliases

     类别名，只能对PO类进行类型别名的定义。

别名	映射的类型
_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