第一个MyBatis程序

# 第一个MyBatis程序💛

# 1、搭建环境

数据库 gokudb
所需Jar包

<!-- mybatis -->
<dependency>
    <groupId>org.mybatis</groupId>
    <artifactId>mybatis</artifactId>
    <version>3.5.6</version>
</dependency>

<!--junit-->
<dependency>
    <groupId>junit</groupId>
    <artifactId>junit</artifactId>
    <version>4.12</version>
    <scope>test</scope>
</dependency>

<!--mysql-connector-java-->
<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>8.0.22</version>
</dependency>

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# 2、mybatis-config.xml配置文件

<?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>
    <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://127.0.0.1:3306/goku?serverTimezone=Asia/Shanghai"/>
                <property name="username" value="root"/>
                <property name="password" value="795200"/>
            </dataSource>
        </environment>
    </environments>
    <!--每一个mapper.xml都需要在MyBatis核心配置文件中注册-->
    <mappers>
        <mapper resource="com/singerw/mapper/UserMapper.xml"/>
    </mappers>
</configuration>

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# 3、编写MyBatisUtils工具类

/**
 * @Author: CodeSleep
 * @Date: 2021/8/23 21:15
 * @Description: //TODO MyBatis工具类
 */
public class MyBatisUtils {
    private static SqlSessionFactory sqlSessionFactory;

    // 加载资源
    static {
        try {
            // 使用MyBatis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();
        }
    }

    /**
     * @return
     * @Author CodeSleep
     * @Date: 2021/8/23 21:13
     * @Description: //TODO 创建执行SQL的对象
     * sqlSessionFactory中获取SqlSession实例
     * SqlSession完全包含了面向数据库执行SQL命令所需的所有方法；
     */
    public static SqlSession getSqlSession() {
        SqlSession sqlSession = sqlSessionFactory.openSession();
        return sqlSession;
    }
}

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# 4、编写代码

实体类（User.java）

@Data
@AllArgsConstructor
@NoArgsConstructor
public class User {
    private int userid;
    private String username;
    private String userphone;
    private String userpassword;
    private int jurisdiction;
    private String createtime;
    private String logintime;
    private int userstatus;
}

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Dao数据持久层接口（UserMapper.java）

public interface UserMapper {

    List<User> getUsers(int userid);
}

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Dao数据持久层（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">
<mapper namespace="com.singerw.mapper.UserMapper">
    <select id="getUsers" resultType="com.singerw.pojo.User">
        select * from goku.g_users where userid = #{userid}
    </select>
</mapper>

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测试类（UserMapperTest.java）

public class UserMapperTest {

    @Test
    public void getUsers() {
        SqlSession sqlSession = MyBatisUtils.getSqlSession();
        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
        List<User> users = userMapper.getUsers(1);
        for (User user : users) {
            System.out.println(user);
        }
        sqlSession.close();
    }
}

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# 5、注意点

在pom.xml的build中配置resources，来防止我们资源在Maven项目中的导出失败的问题！

<!--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>
        </resource>
    </resources>
</build>

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可能会遇到的问题：

配置文件没有注册
绑定接口错误
方法名不对
返回类型不对
Maven导出资源问题

编辑

#MyBatis

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