新版SSM-SpringBoot4.x+Spring7+Mybatis4.x-入门到实战专题课程：2026年后端开发的核武器

xml<dependencyManagement>
    <dependencies>
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis-bom</artifactId>
            <version>4.0.2</version>
            <type>pom</type>
            <scope>import</scope>
        </dependency>
    </dependencies>
</dependencyManagement>

<dependencies>
    <!-- MyBatis 4 核心 -->
    <dependency>
        <groupId>org.mybatis</groupId>
        <artifactId>mybatis</artifactId>
        <version>4.0.2</version>
    </dependency>
    
    <!-- Spring集成 -->
    <dependency>
        <groupId>org.mybatis.spring.boot</groupId>
        <artifactId>mybatis-spring-boot-starter</artifactId>
        <version>3.0.4</version>
    </dependency>
    
    <!-- MySQL驱动 -->
    <dependency>
        <groupId>com.mysql</groupId>
        <artifactId>mysql-connector-j</artifactId>
        <scope>runtime</scope>
    </dependency>
</dependencies>

yamlspring:
  datasource:
    url: jdbc:mysql://localhost:3306/mydb?useSSL=false&serverTimezone=Asia/Shanghai
    username: root
    password: your_password
    driver-class-name: com.mysql.cj.jdbc.Driver
    hikari:
      maximum-pool-size: 20
      minimum-idle: 5

mybatis:
  mapper-locations: classpath:mapper/*.xml   # XML仍支持，但不是必须
  configuration:
    map-underscore-to-camel-case: true       # 下划线转驼峰
    log-impl: org.apache.ibatis.logging.stdout.StdOutImpl  # 开发环境打印SQL
  # MyBatis 4 新增：AI SQL Advisor
  ai-advisor:
    enabled: true
    model: deepseek-coder-v2   # 用DeepSeek当你的SQL顾问

xml<!-- UserMapper.xml -->
<select id="selectById" resultType="User">
    SELECT * FROM user WHERE id = #{id}
</select>
<insert id="insert" parameterType="User">
    INSERT INTO user(name, email) VALUES(#{name}, #{email})
</insert>
<update id="updateById" parameterType="User">
    UPDATE user SET name=#{name}, email=#{email} WHERE id=#{id}
</update>
<delete id="deleteById">
    DELETE FROM user WHERE id = #{id}
</delete>

java@Mapper
public interface UserMapper {
    
    @Select("SELECT * FROM user WHERE id = #{id}")
    User selectById(Long id);
    
    @Insert("INSERT INTO user(name, email) VALUES(#{name}, #{email})")
    @Options(useGeneratedKeys = true, keyProperty = "id")
    int insert(User user);
    
    @Update("UPDATE user SET name=#{name}, email=#{email} WHERE id=#{id}")
    int updateById(User user);
    
    @Delete("DELETE FROM user WHERE id = #{id}")
    int deleteById(Long id);
}

java@Mapper
@CRUD(table = "user", idColumn = "id")  // 一行生成全部CRUD！
public interface UserMapper extends BaseMapper<User> {
    // 自动拥有：selectById / insert / updateById / deleteById / selectAll / count
    // 零XML，零手写SQL！
}

java@Mapper
public interface OrderMapper {
    
    // 写了一段烂SQL？AI自动提示优化
    @Select("""
        SELECT o.*, u.name 
        FROM order o 
        LEFT JOIN user u ON o.user_id = u.id 
        WHERE o.status = #{status}
        """)
    @AIAdvisor(enabled = true)   // 开启AI建议
    List<Order> findByStatus(String status);
}

🤖 AI SQL Advisor:
  ⚠️ 检测到 LEFT JOIN 未使用索引，建议：
     1. 在 order.user_id 上添加索引：CREATE INDEX idx_order_user_id ON order(user_id);
     2. 将 LEFT JOIN 改为 INNER JOIN（如果业务允许），性能提升 40%
  💡 推荐改写：
     SELECT o.id, o.amount, u.name 
     FROM order o 
     INNER JOIN user u ON o.user_id = u.id 
     WHERE o.status = #{status} AND o.create_time > NOW() - INTERVAL 30 DAY

xml<select id="findUsers" resultType="User">
    SELECT * FROM user
    <where>
        <if test="name != null">AND name LIKE CONCAT('%', #{name}, '%')</if>
        <if test="minAge != null">AND age >= #{minAge}</if>
        <if test="maxAge != null">AND age &lt;= #{maxAge}</if>
    </where>
</select>

java@Mapper
public interface UserMapper {
    
    default List<User> findUsers(String name, Integer minAge, Integer maxAge) {
        return select(User.class)
            .from("user")
            .where(name != null, c -> c.like("name", "%" + name + "%"))
            .where(minAge != null, c -> c.ge("age", minAge))
            .where(maxAge != null, c -> c.le("age", maxAge))
            .list();
    }
}

java@Data
public class Order {
    private Long id;
    private String orderNo;
    
    @Lazy(fetch = FetchType.SELECT)   // 只有用到时才查
    private List<OrderItem> items;     // 不再N+1！
    
    @Lazy(fetch = FetchType.JOIN)      // 用JOIN一次查完
    private User user;
}

java@Mapper
public interface OrderMapper {
    
    @Select("SELECT * FROM order WHERE id = #{id}")
    @Result(column = "id", property = "id", 
            one = @One(select = "com.example.mapper.UserMapper.selectById"))
    Order selectById(Long id);
    
    @Select("SELECT * FROM order_item WHERE order_id = #{orderId}")
    List<OrderItem> selectItemsByOrderId(Long orderId);
}

java@Mapper
@MultiTenant(column = "tenant_id", strategy = Strategy.AUTO)
public interface ProductMapper {
    
    @Select("SELECT * FROM product WHERE id = #{id}")
    Product selectById(Long id);
    
    // 自动注入 tenant_id = #{tenantId}
    // 你永远不用手写 AND tenant_id = ?
}

java// 配置多租户解析器
@Bean
public TenantIdResolver tenantIdResolver() {
    return () -> SecurityContextHolder.getContext()
        .getAuthentication()
        .getPrincipal()  // 从JWT/Session中自动获取租户ID
        .toString();
}

java@Mapper
@Transactional(readOnly = true)   // 整个Mapper默认只读
public interface UserMapper {
    
    @Select("SELECT * FROM user WHERE id = #{id}")
    User selectById(Long id);
    
    @Update("UPDATE user SET name=#{name} WHERE id=#{id}")
    @Transactional   // 单个方法覆盖默认，开启写事务
    int updateName(Long id, String name);
}