Mapper 接口开发方法只需要程序员编写Mapper 接口(相当于Dao 接口),由Mybatis 框架根据接口定义创建接 口的动态代理对象,代理对象的方法体同上边Dao接口实现类方法。 Mapper 接口开发需要遵循以下规范:
1、 Mapper.xml文件中的namespace与mapper接口的全限定名相同
2、 Mapper接口方法名和Mapper.xml中定义的每个statement的id相同
3、 Mapper接口方法的输入参数类型和mapper.xml中定义的每个sql的parameterType的类型相同
4、 Mapper接口方法的输出参数类型和mapper.xml中定义的每个sql的resultType的类型相同
即:
最后我们要获取Mybatis给我们生成的代理对象 ,是用 sqlSession.getMapper 这个方法获取的!!!!
实操:
这是结构
package com.bihu.Dao;
import com.bihu.Bean.User;
import java.util.List;
public interface UserMapper {
public List<User> findAll();
}
Mapper.class 映射接口
<?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="com.bihu.Dao.UserMapper">
<select id="findAll" resultType="User" > <!--这里的User前面有别名-->
select * from user
</select>
</mapper>
Mapper.xml 映射文件
<?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>
<properties resource="datasourceInfo.properties"></properties>
<typeAliases>
<typeAlias type="com.bihu.Bean.User" alias="User"></typeAlias>
</typeAliases>
<environments default="dev">
<environment id="dev">
<transactionManager type="JDBC"></transactionManager>
<dataSource type="POOLED">
<property name="driver" value="${jdbc.driver}"/>
<property name="url" value="${jdbc.url}"/>
<property name="username" value="${jdbc.username}"/>
<property name="password" value="${jdbc.password}"/>
</dataSource>
</environment>
</environments>
<mappers>
<mapper resource="com/bihu/mapper/UserMapper.xml"></mapper>
</mappers>
</configuration>
sqlMapConfig.xml mybatis核心配置文件
package com.bihu.Service;
import com.bihu.Bean.User;
import com.bihu.Dao.UserMapper;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import java.io.IOException;
import java.io.InputStream;
import java.util.List;
public class UserService {
public static void main(String[] args) throws IOException {
InputStream sqlMapConfig = Resources.getResourceAsStream("SqlMapConfig.xml");
SqlSessionFactory build = new SqlSessionFactoryBuilder().build(sqlMapConfig);
SqlSession sqlSession = build.openSession();
UserMapper mapper = sqlSession.getMapper(UserMapper.class); //获取动态对象
List<User> all = mapper.findAll(); //执行查询所有方法
System.out.println(all); //打印
}
}
Serivce 业务层代码
下面来个按条件查询操作 带参数的:
其实就是准守最上面4条即可 非常的简单:
首先写接口:
然后对应的namespace确保对应接口,而且参数类型和结果类型(结果类型只算泛型)对应!
确保那几个下面就可以获取动态对象了:
package com.bihu.Service;
import com.bihu.Bean.User;
import com.bihu.Dao.UserMapper;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import java.io.IOException;
import java.io.InputStream;
import java.util.List;
public class UserService {
public static void main(String[] args) throws IOException {
InputStream sqlMapConfig = Resources.getResourceAsStream("SqlMapConfig.xml");
SqlSessionFactory build = new SqlSessionFactoryBuilder().build(sqlMapConfig);
SqlSession sqlSession = build.openSession();
UserMapper mapper = sqlSession.getMapper(UserMapper.class); //获取动态对象
User user = new User();//模拟有User数据【其实单单查一个ID推荐用Integer即可 但这里没有。】
user.setId(5);
List<User> userList = mapper.findId(user);
System.out.println(userList);
}
}
业务层 模拟
允许:
说白了 其实单单一个Id 直接用Integer 但这里我为了演示参数就没那样做
作者:咸瑜