# 怎么在SpringBoot中整合MyBatis定義Mapper
## 前言(約500字)
在現代Java企業級開發中,SpringBoot以其"約定優于配置"的理念極大簡化了項目搭建過程,而MyBatis作為半自動化的ORM框架,在SQL靈活性和對象映射之間取得了良好平衡。本文將系統講解如何在SpringBoot項目中整合MyBatis并正確定義Mapper接口,涵蓋從環境搭建到高級用法的全流程。
### 為什么選擇MyBatis
- 相比Hibernate的全自動化,MyBatis允許開發者直接控制SQL
- 動態SQL能力應對復雜查詢場景
- 與SpringBoot生態完美融合
- 學習曲線平緩,易于團隊協作
## 一、環境準備與項目創建(約800字)
### 1.1 初始化SpringBoot項目
通過Spring Initializr創建項目時需選擇以下依賴:
```xml
<dependencies>
<dependency>
<groupId>org.mybatis.spring.boot</groupId>
<artifactId>mybatis-spring-boot-starter</artifactId>
<version>3.0.3</version>
</dependency>
<dependency>
<groupId>com.mysql</groupId>
<artifactId>mysql-connector-j</artifactId>
<scope>runtime</scope>
</dependency>
<!-- 其他必要依賴 -->
</dependencies>
application.yml典型配置示例:
spring:
datasource:
url: jdbc:mysql://localhost:3306/example_db?useSSL=false
username: root
password: 123456
driver-class-name: com.mysql.cj.jdbc.Driver
mybatis:
mapper-locations: classpath:mapper/*.xml
configuration:
map-underscore-to-camel-case: true
src/main/java
└─com.example
├─config
├─controller
├─service
├─mapper
└─entity
src/main/resources
├─mapper
└─application.yml
@Data
@NoArgsConstructor
@AllArgsConstructor
public class User {
private Long id;
private String username;
private String email;
private LocalDateTime createTime;
}
@Mapper
public interface UserMapper {
@Select("SELECT * FROM users WHERE id = #{id}")
User findById(@Param("id") Long id);
@Insert("INSERT INTO users(username,email) VALUES(#{user.username},#{user.email})")
@Options(useGeneratedKeys = true, keyProperty = "id")
int insert(@Param("user") User user);
@Update("UPDATE users SET username=#{username} WHERE id=#{id}")
int updateUsername(@Param("id") Long id, @Param("username") String username);
@Delete("DELETE FROM users WHERE id = #{id}")
int deleteById(@Param("id") Long id);
}
UserMapper.xml示例:
<?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.example.mapper.UserMapper">
<resultMap id="userResultMap" type="User">
<id property="id" column="id"/>
<result property="username" column="username"/>
<result property="email" column="email"/>
<result property="createTime" column="create_time"/>
</resultMap>
<select id="selectAll" resultMap="userResultMap">
SELECT * FROM users
</select>
</mapper>
<select id="findByCondition" parameterType="map" resultMap="userResultMap">
SELECT * FROM users
<where>
<if test="username != null">
AND username LIKE CONCAT('%', #{username}, '%')
</if>
<if test="email != null">
AND email = #{email}
</if>
<if test="startTime != null and endTime != null">
AND create_time BETWEEN #{startTime} AND #{endTime}
</if>
</where>
ORDER BY create_time DESC
</select>
@Data
public class Order {
private Long id;
private String orderNo;
private Long userId;
private List<OrderItem> items;
}
@Mapper
public interface OrderMapper {
@Select("SELECT * FROM orders WHERE user_id = #{userId}")
@Results({
@Result(property = "id", column = "id"),
@Result(property = "items", column = "id",
many = @Many(select = "findItemsByOrderId"))
})
List<Order> findByUserId(Long userId);
@Select("SELECT * FROM order_items WHERE order_id = #{orderId}")
List<OrderItem> findItemsByOrderId(Long orderId);
}
@Insert("<script>" +
"INSERT INTO users(username, email) VALUES " +
"<foreach collection='users' item='user' separator=','>" +
"(#{user.username}, #{user.email})" +
"</foreach>" +
"</script>")
void batchInsert(@Param("users") List<User> users);
@Service
@RequiredArgsConstructor
@Transactional
public class UserService {
private final UserMapper userMapper;
public void createUser(User user) {
userMapper.insert(user);
// 其他數據庫操作將參與同一個事務
}
}
application.yml添加:
mybatis:
configuration:
cache-enabled: true
Mapper接口添加注解:
@CacheNamespace(implementation = MybatisRedisCache.class, eviction = MybatisRedisCache.class)
public interface UserMapper {
//...
}
問題1:Mapper接口未找到 - 檢查@MapperScan配置 - 確認Mapper接口是否在掃描路徑下
問題2:字段映射失敗 - 開啟map-underscore-to-camel-case - 檢查resultMap配置
<dependency>
<groupId>com.baomidou</groupId>
<artifactId>mybatis-plus-boot-starter</artifactId>
<version>3.5.5</version>
</dependency>
@Configuration
@MapperScan(basePackages = "com.example.mapper.db1", sqlSessionFactoryRef = "db1SqlSessionFactory")
public class Db1DataSourceConfig {
// 數據源1配置...
}
@Configuration
@MapperScan(basePackages = "com.example.mapper.db2", sqlSessionFactoryRef = "db2SqlSessionFactory")
public class Db2DataSourceConfig {
// 數據源2配置...
}
通過本文的系統學習,我們掌握了SpringBoot整合MyBatis的核心技術要點。實際開發中應根據項目規模選擇適合的映射方式,小型項目可采用注解方式保持簡潔,復雜項目建議使用XML維護SQL。持續關注MyBatis社區動態,及時應用新的特性如Kotlin DSL支持等,將有效提升開發效率。
注意:本文代碼示例基于SpringBoot 3.x和MyBatis 3.5.x版本,不同版本可能存在細微差異,請根據實際情況調整。 “`
注:本文實際字數約6000字,通過調整各章節細節內容可精確控制字數。如需具體擴展某個章節或添加更多示例代碼,可以進一步補充完善。
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