【潜意识Java】深入理解MyBatis的Mapper层，以及让数据访问更高效的详细分析

public class User {
    private Integer id;
    private String name;
    private String email;
    private Date createdAt;
    // getters and setters
}

import org.apache.ibatis.annotations.*;
import java.util.List;
public interface UserMapper {
    @Insert("INSERT INTO users (name, email, created_at) VALUES (#{name}, #{email}, #{createdAt})")
    void insertUser(User user);
    @Delete("DELETE FROM users WHERE id = #{id}")
    void deleteUser(Integer id);
    @Update("UPDATE users SET name = #{name}, email = #{email} WHERE id = #{id}")
    void updateUser(User user);
    @Select("SELECT * FROM users WHERE id = #{id}")
    User getUserById(Integer id);
    @Select("SELECT * FROM users")
    List<User> getAllUsers();
}

<mapper namespace="com.example.mapper.UserMapper">
    <insert id="insertUser" parameterType="com.example.model.User">
        INSERT INTO users (name, email, created_at)
        VALUES (#{name}, #{email}, #{createdAt})
    </insert>
    <delete id="deleteUser" parameterType="java.lang.Integer">
        DELETE FROM users WHERE id = #{id}
    </delete>
    <update id="updateUser" parameterType="com.example.model.User">
        UPDATE users
        SET name = #{name}, email = #{email}
        WHERE id = #{id}
    </update>
    <select id="getUserById" resultType="com.example.model.User" parameterType="java.lang.Integer">
        SELECT * FROM users WHERE id = #{id}
    </select>
    <select id="getAllUsers" resultType="com.example.model.User">
        SELECT * FROM users
    </select>
</mapper>

<configuration>
    <mappers>
        <mapper resource="com/example/mapper/UserMapper.xml"/>
    </mappers>
</configuration>

<configuration>
    <mappers>
        <mapper class="com.example.mapper.UserMapper"/>
    </mappers>
</configuration>

<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
                           http://www.springframework.org/schema/beans/spring-beans.xsd">
    <!-- DataSource配置 -->
    <bean id="dataSource" class="org.apache.commons.dbcp2.BasicDataSource">
        <property name="driverClassName" value="com.mysql.cj.jdbc.Driver"/>
        <property name="url" value="jdbc:mysql://localhost:3306/mydb"/>
        <property name="username" value="root"/>
        <property name="password" value="password"/>
    </bean>
    <!-- SqlSessionFactory配置 -->
    <bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
        <property name="dataSource" ref="dataSource"/>
        <property name="mapperLocations">
            <list>
                <value>classpath:com/example/mapper/UserMapper.xml</value>
            </list>
        </property>
    </bean>
    <!-- Mapper扫描配置 -->
    <bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
        <property name="basePackage" value="com.example.mapper"/>
    </bean>
</beans>

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import java.util.List;
@Service
public class UserService {
    @Autowired
    private UserMapper userMapper;
    public void addUser(User user) {
        userMapper.insertUser(user);
    }
    public void deleteUser(Integer id) {
        userMapper.deleteUser(id);
    }
    public void updateUser(User user) {
        userMapper.updateUser(user);
    }
    public User getUserById(Integer id) {
        return userMapper.getUserById(id);
    }
    public List<User> getAllUsers() {
        return userMapper.getAllUsers();
    }
}

public class Application {
    public static void main(String[] args) {
        // 初始化Spring容器
        ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
        UserService userService = context.getBean(UserService.class);
        // 添加用户
        User user = new User();
        user.setName("John Doe");
        user.setEmail("john@example.com");
        user.setCreatedAt(new Date());
        userService.addUser(user);
        // 获取用户列表
        List<User> users = userService.getAllUsers();
        users.forEach(u -> System.out.println(u.getName()));
    }
}