前言
作者: Ant QQ:517377100
相对于使用JdbcTemplate，Mybatis可自动建立pojo类型与数据库列的映射关系，数据库访问层的开发简单了许多
所有数据库访问操作，均封装在各个Mapper接口中，接口的实现即为数据库sql操作，sql可以注解的形式提供，也可以定义在xml文件中（复杂的sql操作优选xml）
引入Mybatis框架步骤简单，这里做一些整理
本人集成开发环境使用 Intellij
添加Mybatis依赖项
pom.xml增加如下依赖项
<dependency>
<groupId>org.mybatis</groupId>
<artifactId>mybatis</artifactId>
<version>3.2.8</version>
</dependency>
<dependency>
<groupId>org.mybatis</groupId>
<artifactId>mybatis-spring</artifactId>
<version>1.2.2</version>
</dependency>
Bean声明
相关Bean的声明统一在DatabaseConfiguration类型中
其中包含了UserMapper、CommodityMapper、CommodityCategoryMapper三个Bean的声明
代码如下
@Configuration
public class DatabaseConfiguration {
@Bean
public DataSource dataSource() {
...
}
@Bean
public SqlSessionFactory sqlSessionFactory() throws Exception {
SqlSessionFactoryBean sqlSessionFactoryBean = new SqlSessionFactoryBean();
sqlSessionFactoryBean.setDataSource(dataSource());
sqlSessionFactoryBean.setTypeAliases(new Class[]{User.class, Commodity.class, CommodityCategory.class});
sqlSessionFactoryBean.getObject().getConfiguration().setMapUnderscoreToCamelCase(true);
return sqlSessionFactoryBean.getObject();
}
private <T> MapperFactoryBean getMapper(Class<T> mapperInterface) {
MapperFactoryBean<T> mapperFactoryBean = new MapperFactoryBean<T>();
try {
mapperFactoryBean.setSqlSessionFactory(sqlSessionFactory());
mapperFactoryBean.setMapperInterface(mapperInterface);
} catch (Exception ex) {
logger.error("error when create mapper: ", ex);
throw new RuntimeException(ex);
}
return mapperFactoryBean;
}
@Bean
public MapperFactoryBean userMapper() {
return getMapper(UserMapper.class);
}
@Bean
public MapperFactoryBean commodityCategoryMapper() {
return getMapper(CommodityCategoryMapper.class);
}
@Bean
public MapperFactoryBean commodityMapper() {
return getMapper(CommodityMapper.class);
}
}
创建SqlSessionFactory的同时，将其配置项MapUnderscoreToCamelCase设置为true，如数据库列 user_name将自动映射到pojo中的userName属性
通过setTypeAliases，指定使用的Pojo类型，后续Mapper.xml中就不需要指定Pojo类型的完整限定名（即无需指定namespace）
Mapper interface
package com.antsoft.docoding.mapper;
import java.util.List;
import com.antsoft.docoding.model.User;
public interface UserMapper {
List<User> getUsers();
User getUser(long id);
void addUser(User user);
void clear();
void updateUser(User user);
}
Mapper xml
Mapper.xml所在目录需要与对应的Mapper接口位于统一个包中
上述UserMapper接口，对应的UserMapper.xml 位于目录resources/com/antsoft/docoding/mapper/中，内容如下
<?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.antsoft.docoding.mapper.UserMapper">
<resultMap id="user" type="user">
<result column="user_type" property="userType" typeHandler="org.apache.ibatis.type.EnumOrdinalTypeHandler"/>
</resultMap>
<delete id="clear">
DELETE FROM dc_user
</delete>
<select id="getUsers" resultMap="user">
SELECT id, user_name, user_type FROM dc_user
</select>
<select id="getUser" resultMap="user">
SELECT id, user_name, user_type FROM dc_user WHERE id = #{id}
</select>
<insert id="addUser" useGeneratedKeys="true" keyProperty="id" parameterType="user">
INSERT INTO dc_user(user_name, user_type)
VALUES(#{userName}, #{userType, typeHandler=org.apache.ibatis.type.EnumOrdinalTypeHandler})
</insert>
<update id="updateUser" parameterType="user">
UPDATE dc_user SET user_name = #{userNmae},
user_type = #{userType, typeHandler=org.apache.ibatis.type.EnumOrdinalTypeHandler}
WHERE id = #{id}
</update>
</mapper>
关于EnumOrdinalTypeHandler，可以完成枚举值叙述与枚举类型的自动转换
使用Mapper
使用Mapper的方式与以前使用Dao类型的方法完全一致，通过@Autowired实现依赖注入，如下：
@Service
public class UserService {
@Autowired
private UserMapper userMapper;
public void clear() {
userMapper.clear();
}
public List<User> getUsers() {
return userMapper.getUsers();
}
public void addUser(User user) {
userMapper.addUser(user);
}
public void updateUser(User user) {
userMapper.updateUser(user);
}
public User getUser(long id) {
return userMapper.getUser(id);
}
}