Mybatis环境配置

搭建环境

也可根据官方文档来进行配置https://mybatis.org/mybatis-3/zh/index.html

以下的内容配置均为经过实验的

pom.xml配置

<!--    导入依赖-->
    <dependencies>
<!--        mysql驱动-->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.15</version>
        </dependency>
<!--        mybatis-->
        <!-- https://mvnrepository.com/artifact/org.mybatis/mybatis -->
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.7</version>
        </dependency>

        <!--        junit-->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.13.1</version>
            <scope>test</scope>
        </dependency>
    </dependencies>
    <!--在build中配置resources，来防止我们资源导出失败的问题-->
    <build>
        <resources>
            <resource>
                <directory>src/main/resources</directory>
                <includes>
                    <include>**/*.properties</include>
                    <include>**/*.xml</include>
                </includes>
            </resource>
            <resource>
                <directory>src/main/java</directory>
                <includes>
                    <include>**/*.properties</include>
                    <include>**/*.xml</include>
                </includes>
                <filtering>true</filtering>
            </resource>
        </resources>
    </build>

编写xml核心配置文件

在resources包下创建一个xml文件，文件名为:mybatis-config.xml

修改配置文件中driver、url、username、password、resource的value

如果报错，可以将开头的UTF-8改为UTF8或者删除xml中的注释

<?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?serverTimezone=Asia/Shanghai&amp;useSSL=true&amp;useUnicode=true&amp;characterEncoding=UTF-8"/>
<!--                <property name="url" value="jdbc:mysql://localhost:3306/mybatis?serverTimezone=Asia/Shanghai&amp;useSSL=false"/>-->
                <property name="username" value="root"/>
                <property name="password" value="root"/>
            </dataSource>
        </environment>
    </environments>
<!--    每一个mapper.xml都需要在Mybatis核心配置中注册-->
    <mappers>
        <mapper resource="com/lzj/dao/UserMapper.xml"/>
    </mappers>
</configuration>

编写Mybatis工具类

//sqlSessionFactory --> sqlSession
public class MybatisUtils {
    private  static SqlSessionFactory sqlSessionFactory;
    static {
        try {
            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(){
//        SqlSession sqlSession = sqlSessionFactory.openSession();
//        return sqlSession;//下一行为优化后的结果
        return sqlSessionFactory.openSession();
    }

}

编写实体类、Dao接口和接口实现类

实体类User

Dao接口

public interface UserDao {
    List<User> getUserList();
}

接口实现类

由原来的UserDaoImpl转变为一个xml配置文件，文件名：UserMapper.xml

如果报错，可以将开头的UTF-8改为UTF8或者删除xml中的注释

<?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.lzj.dao.UserDao">
<!--    select查询-->
<!--    id对应接口方法的名字-->
    <select id="getUserList" resultType="com.lzj.entity.User">
        select * from mybatis.user
    </select>
</mapper>

测试

public class UserDaoTest {
    @Test
    public void test() {
        //获得SqlSession对象
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        //方式一:通过getMapper执行SQL
        UserDao mapper = sqlSession.getMapper(UserDao.class);
        List<User> userList = mapper.getUserList();
        for (User user : userList) {
            System.out.println(user);
        }
        
        //方式二:不推荐这种方式
        List<User> userList1 = sqlSession.selectList("com.lzj.dao.UserDao.getUserList");
        for (User user : userList1) {
            System.out.println(user);
        }
        
        //关闭SqlSession对象
        sqlSession.close();


    }
}

可能遇到的问题

• maven资源无法导入xml的问题
  • 将xml中首行的的UTF-8改为UTF8
  • 将注释删除
• 数据库连接不上的问题
  • 这个就需要自己排查mybatis-config.xml文件中的配置是否正确，url是否能够读取