MyBatis 第一个程序

使用 MyBatis 操作数据库的第一个程序。

一、数据库

user 表

表结构如下：

表数据如下：

二、项目结构

三、项目文件

1. pom.xml

  • 添加依赖
  • 手动配置，以在编译时导出 java 目录下的 xml 文件
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<properties>
    <maven.compiler.source>8</maven.compiler.source>
    <maven.compiler.target>8</maven.compiler.target>
</properties>

<dependencies>
    <!--MySQL驱动-->
    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>5.1.46</version>
    </dependency>
    <!--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>
        <scope>test</scope>
    </dependency>
</dependencies>

<build>
    <resources>
        <resource>
            <directory>src/main/java</directory>
            <includes>
            	<include>**/*.xml</include>
            </includes>
            <filtering>true</filtering>
        </resource>
    </resources>
</build>

2. mybatis-config.xml

配置数据库相关信息

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<?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://localhost:3306/idb"/>
                <property name="username" value="root"/>
                <property name="password" value="root"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="dao/UserMapper.xml"/>
    </mappers>
</configuration>

3. User.java

User 实体类

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public class User {
    private int id;
    private String username;
    private String password;

    // 构造方法
    
    // Getter and Setter
    
    // 重写 toString() 方法
    
}

4. MyBatisUtils.java

  • 构建 SqlSessionFactory
  • 提供获取 SqlSession 实例的类方法
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public class MyBatisUtils {

    private static SqlSessionFactory sqlSessionFactory;

    static {
        try {
            // 获取 SqlSessionFactory 对象
            String resource = "mybatis-config.xml";
            InputStream resourceInputStream = Resources.getResourceAsStream(resource);
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceInputStream);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    // 获取 SqlSession 实例
    public static SqlSession getSqlSession() {
        return sqlSessionFactory.openSession();
    }
}

5. UserMapper.java

抽象类，定义数据操作方法

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

6. UserMapper.xml

定义 SQL 映射

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<?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="dao.UserMapper">
    <select id="getUserList" resultType="pojo.User">
        select * from user
    </select>
</mapper>

四、运行测试

1. UserMapperTest.java

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public class UserMapperTest {
    @Test
    public void testGetUserList() {
        // 获取 sqlSession 对象
        SqlSession sqlSession = MyBatisUtils.getSqlSession();
        // 获取 mapper 实例
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        // 调用方法，执行 SQL
        List<User> userList = mapper.getUserList();
        for (User user : userList) {
            System.out.println(user);
        }
        // 关闭 sqlSession
        sqlSession.close();
    }
}

2. 运行结果

参考