Java Mybatis快速入门之基本使用
搭建环境
新建Maven项目
导入Maven依赖
<dependencies>
<!--mysql驱动-->
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>5.1.47</version>
</dependency>
<!--Mybatis-->
<!-- https://mvnrepository.com/artifact/org.mybatis/mybatis -->
<dependency>
<groupId>org.mybatis</groupId>
<artifactId>mybatis</artifactId>
<version>3.5.2</version>
</dependency>
<!--junit-->
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.12</version>
</dependency>
</dependencies>
编写 Mybatis 核心配置文件
1.核心配置文件
mybatis-config.xml
注意, 在 xml
中 &
需要转义, 应该使用 &
<?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">
<!--核心配置文件-->
<configuration>
<environments default="development">
<environment id="development">
<transactionManager type="JDBC"/>
<dataSource type="POOLED">
<property name="driver" value="com.mysql.jdbc.Driver"/>
<property name="url" value="jdbc:mysql://localhost:3306/mybatis?useSSL=true&useUnicode=true&characterEncoding=UTF-8"/>
<property name="username" value="root"/>
<property name="password" value="123456"/>
</dataSource>
</environment>
</environments>
</configuration>
2.编写Mybatis工具类
package com.pro.utils;
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;
// SqlSessionFactory --> SqlSession
public class MybatisUtils {
private static SqlSessionFactory sqlSessionFactory;
static {
try {
// 获取 SqlSessionFactory 对象
String resource = "mybatis-config.xml";
InputStream inputStream = Resources.getResourceAsStream(resource);
sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
} catch (IOException e) {
e.printStackTrace();
}
}
// 既然有了 SqlSessionFactory,顾名思义,我们可以从中获得 SqlSession 的实例。SqlSession 提供了在数据库执行 SQL 命令所需的所有方法
public static SqlSession getSqlSession() {
return sqlSessionFactory.openSession();
}
}
3.编写接口
package com.pro.dao;
import com.pro.pojo.User;
import java.util.List;
public interface UserDao {
public List<User> getUserList();
}
4.由原来的实现类转变为一个 Mapper 配置文件 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: 绑定一个对应的 Dao/Mapper 接口-->
<mapper namespace="com.pro.dao.UserDao">
<!-- id 绑定接口中方法 -->
<select id="getUserList" resultType="com.pro.pojo.User">
select * from user
</select>
</mapper>
pom导出资源失败
<!--在pom.xml中配置build, 来防止我们资源导出失败问题-->
<build>
<resources>
<resource>
<directory>src/main/resources</directory>
<includes>
<include>**/*.properties</include>
<include>**/*.xml</include>
</includes>
<filtering>true</filtering>
</resource>
<resource>
<directory>src/main/java</directory>
<includes>
<include>**/*.properties</include>
<include>**/*.xml</include>
</includes>
<filtering>true</filtering>
</resource>
</resources>
</build>
测试
注意点
org.apache.ibatis.binding.BindingException: Type interface com.pro.dao.UserDao is not known to the MapperRegistry.
MapperRegistry
在核心配置文件中注册 mapper, 每一个 Mapper.xml 都需要在 Mybatis 核心配置文件中注册
<!-- 每一个 Mapper.xml 都需要在 Mybatis 核心配置文件中注册 -->
<mappers>
<mapper resource="com/pro/dao/UserMapper.xml"></mapper>
</mappers>
junit测试
package com.pro.dao;
import com.pro.pojo.User;
import com.pro.utils.MybatisUtils;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;
import java.util.List;
public class UserDaoTest {
@Test
public void test() {
// 获取 sqlSession 对象
SqlSession sqlSession = MybatisUtils.getSqlSession();
// 执行 SQL 方式一: getMapper
UserDao mapper = sqlSession.getMapper(UserDao.class);
List<User> userList = mapper.getUserList();
for (User user : userList) {
System.out.println(user);
}
// 关闭资源
sqlSession.close();
}
}