SSM系列——Mybatis相应API
相应API
SqlSessionFactoryBuilder工厂构建器
SqlSessionFactoryBuilder().build(InputStream inputStream):通过加载mybatis的核心文件的输入流的形式构建一个SqlSessionFactory对象
//加载核心配置文件
InputStream resource = Resources.getResourceAsStream("config/sqlMapperConfi.xml");
//获得sqlSession工厂对象
SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(resource);
SqlSessionFactory工厂对象
用于创建sqlSession实例
常用有
- openSession():会默认开启一个事务,但事务不会自动提交,也就意味着需要手动提交该事务,更新操作数据才会持久化到数据车中
- openSession(boolean autoCommit):参数为是否自动提交,如果设置为true,那么不需要手动提交事务
//获取sqlSession会话对象
//手动提交
SqlSession sqlSession = factory.openSession();
//自动提交
SqlSession sqlSession = factory.openSession(true);
SqlSession会话对象
SqlSession实例在MyBatis中是非常强大的一个类。在这里你会看到所有执行语句、提交或回滚事务和获取映射器实例的方法。
执行语句的方法主要有:
<T> T selectOne(String statement);
<E> List<E> selectList(String statement);
<K, V> Map<K, V> selectMap(String statement, String mapKey);
void select(String statement, Object parameter, ResultHandler handler);
int insert(String statement, Object parameter);
int update(String statement, Object parameter);
int delete(String statement, Object parameter);
void commit();
void rollback();
代理开发
采用Mybatis的代理开发方式实现DAO层的开发,这种方式是我们后面进入企业的主流。
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:
- Mapper.xml文件中的namespace与mapper接口的全限定名相同
- Mapper接口方法名和Mapper.xml中定义的每个statement的id相同
- 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
- 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
关键点
使用getMapper方法获取映射sql
例子:
UserMapper mapper = sqlSession.getMapper(UserMapper.class);
namespace命名空间对应Mapper接口
例子:
<mapper namespace="com.example.mybatis.mapper.UserMapper">
示例代码
目录
对应关系
1.创建User实体类
package com.example.mybatis.entity;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
@Data
@AllArgsConstructor
@NoArgsConstructor
public class User {
private Long id;
private String username;
private String password;
}
2.创建UserMapper接口
package com.example.mybatis.mapper;
import com.example.mybatis.entity.User;
import java.io.IOException;
import java.util.List;
public interface UserMapper {
public List<User> findAll() throws IOException;
public List<User> findById(Long id);
}
3.创建UserMapper.xml配置
<?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.example.mybatis.mapper.UserMapper">
<select id="findAll" resultType="user">
select *
from user
</select>
<select id="findById" resultType="user" parameterType="long">
select *
from user
where id = #{id}
</select>
</mapper>
4.创建sqlMapperConfig.xml进行配置
<?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">
<!--数据源环境-->
<configuration>
<properties resource="properties/jdbc.properties"></properties>
<!-- 自定义别名-->
<typeAliases>
<typeAlias type="com.example.mybatis.entity.User" alias="user"></typeAlias>
</typeAliases>
<environments default="development">
<environment id="development">
<transactionManager type="JDBC"/>
<dataSource type="POOLED">
<property name="driver" value="${driverClassName}"/>
<property name="url"
value="${url}"/>
<property name="username" value="${username}"/>
<property name="password" value="${password}"/>
</dataSource>
</environment>
</environments>
<!-- 加载映射文件-->
<mappers>
<mapper resource="mapper/UserMapper.xml"/>
</mappers>
</configuration>
5.抽取出jdbc.properties
driverClassName=com.mysql.cj.jdbc.Driver
url=jdbc:mysql://localhost:3306/syf?useUnicode=true&characterEncoding=UTF-8&useSSL=false&serverTimezone=Asia/Shanghai&zeroDateTimeBehavior=CONVERT_TO_NULL&allowPublicKeyRetrieval=true
username=root
password=syf20020816
6.测试
package com.example.mybatis;
import com.example.mybatis.entity.User;
import com.example.mybatis.mapper.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 Application {
public static void main(String[] args) throws IOException {
InputStream resource = Resources.getResourceAsStream("config/sqlMapperConfi.xml");
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resource);
SqlSession sqlSession = sqlSessionFactory.openSession();
UserMapper mapper = sqlSession.getMapper(UserMapper.class);
List<User> list = mapper.findAll();
List<User> user = mapper.findById(2L);
user.forEach(System.out::println);
System.out.println("-----------------");
list.forEach(System.out::println);
}
}