Spring Boot 整合 MyBatis 连接数据库及常见问题

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《SpringBoot整合MyBatis连接数据库及常见问题》MyBatis是一个优秀的持久层框架,支持定制化SQL、存储过程以及高级映射,下面详细介绍如何在SpringBoot项目中整合My...

一、基本配置

1. 添加依赖

在pom.xml中添加以下依赖：

<!-- Spring Boot Starter Web -->
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
</dependency>
<!-- MyBatis Spring Boot Starter -->
<dependency>
    <groupId>org.mybatis.spring.boot</groupId>
    <artifactId>mybatis-spring-boot-starter</artifactId>
    <version>2.2.0</version> <!-- 使用最新版本 -->
</dependency>
<!-- 数据库驱动，根据你的数据库选择 -->
<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-Java</artifactId>javascript;
    <scope>runtime</scope>
</dependency>
<!-- 其他可能需要的依赖 -->
<dependency>
    <groupId>com.alibaba</groupId>
    <artifactId>druid-spring-boot-starter</artifactId>
    <version>1.2.6</version> <!-- Druid 连接池 -->
</dependency>

2. 配置数据库连接

在application.yml或application.properties中配置数据库连接：

# application.yml 配置示例
spring:
  datasource:
    url: jdbc:mysql://localhost:3306/your_database?useSSL=false&serverTimezone=UTC&characterEncoding=utf8
    username: your_username
    password: your_password
    driver-class-name: com.mysql.cj.jdbc.Driver
    type: com.alibaba.druid.pool.DruidDataSource # 使用Druid连接池
# MyBatis 配置
mybatis:
  mapper-locations: classpath:mapper/*.xml  # mapper.xml文件位置
  type-aliases-package: com.example.model   # 实体类所在包
  configuration:
    map-underscore-to-camel-case: true      # 开启驼峰命名转换

二、项目结构

典型的项目结构如下：

src/main/java
└── com.example.demo
    ├── DemoApplication.java          # 启动类
    ├── config
    │   └── MyBatisConfig.java        # MyBatis配置类(可选)
    ├── controller
    │   └── UserController.java       # 控制器
    ├── service
    │   ├── UserService.java          # 服务接口
    │   └── impl
    │       └── UserServiceImpl.java  # 服务实现
    ├── mapper
    │   └── UserMapper.java           # Mapper接口
    └── model
        └── User.java                 # 实体类
src/main/resources
├── application.yml                   # 配置文件
└── mapper
    └── UserMapper.xml                # SQL映射文件

三、核心组件实现（示例）

1. 实体类

package com.example.model;
public class User {
    private Long id;
    private String username;
    private String password;
    private String email;
    // getters and setters
    // toString()
}

2. Mapper 接口

package com.example.mapper;
import com.example.model.User;
import org.apache.ibatis.annotations.*;
import java.util.List;
@Mapper // 重要：标识这是一个MyBatis的Mapper接口
public interface UserMapper {
    @Select("SELECT * FROM user WHERE id = #{id}")
    User findById(Long id);
    @Insert("INSERT INTO user(username, password, email) VALUES(#{username}, #{password}, #{email})")
    @Options(useGeneratedKeys = true, keyProperty = "id")
    int insert(User user);
    @Update("UPDATE user SET username=#{username}, password=#{password}, email=#{email} WHERE id=#{id}")
    int update(User user);
    @Delete("DELETE FROM user WHERE id=#{id}")
    int delete(Long id);
    // XML配置方式
    List<User> findAll();
}

3. Mapper XML 文件

src/main/resources/mapper/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.example.mapper.UserMapper">
    <resultMap id="userResultMap" type="User">
        <id property="id" column="id"/>
        <result property="username" column="username"/>
        <result property="password" column="password"/>
        <result property="email" column="email"/>
    </resultMap>
    <select id="findAll" resultMap="userResultMap">
        SELECT * FROM user
    </select>
</mapper>

4. Service 层

package com.example.service;
import com.example.model.Usjser;
import java.util.List;
public interface UserService {
    User findById(Long id)android;
    List<User> findAll();
    int save(User user);
    int update(User user);
    int delete(Long id);
}

service层实现类：

package com.example.service.impl;
import com.example.mapper.UserMapper;
import com.example.model.User;
import com.example.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import java.util.List;
@Service
public class UserServiceImpl implements UserService {
    @Autowired
    private UserMapper userMapper;
    @Override
    public User findById(Long id) {
        return userMapper.findById(id);
    }
    @Override
    public List<User> findAll() {
        return userMapper.findAll();
    }
    @Override
    public int save(User user) {
        return userMapper.insert(user);
    }
    @Override
    public int update(User user) {
        return userMapper.update(user);
    }
    @Override
    public int delete(Long id) {
        return userMapper.delete(id);
    }
}

5. Controller 层：

package com.example.controller;
import com.example.model.User;
import com.example.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.*;
import java.util.List;
@RestController
@RequestMapping("/users")
public class UserController {
    @Autowired
    private UserService userService;
    @GetMapping("/{id}")
    public User getUser(@PathVariable Long id) {
        return userService.findById(id);
    }
    @GetMapping
    public List<User> getAllUsers() {
        return userService.findAll();
    }
    @PostMapping
    public int createUser(@RequestBody User user) {
        return userService.save(user);
    }
    @PutMapping
    public int updateUser(@RequestBody User user) {
        return userService.update(user);
    }
    @DeleteMapping("/{id}")
    public int deleteUser(@PathVariable Long id) {
        return userService.delete(id);
    }
}

四、高级特性

1. 动态SQL

在XML中使用动态SQL：

<select id="findByCondition" parameterType="map" resultMap="userResultMap">
    SELECT * FROM user
    <where>
        <if test="username != null and username != ''">
            AND username LIKE CONCAT('%', #{username}, '%')
        </if>
        <if test="email != null and email != ''">
            AND email = #{email}
        </if>
    </where>
</select>

2. 分页查询

使用PageHelper插件：

添加依赖：

<select id="findByCondition" parameterType="map" resultMap="userResultMap">
    SELECT * FROM user
    <where>
        <if test="username != null and username != ''">
            AND username LIKE CONCAT('%', #{username}, '%')
        </if>
        <if test="email != null and email != ''">
            AND email = #{email}
        </if>
    </where>
</select>

使用示例：

<dependency>
    <groupId>com.github.pagehelper</groupId>
    <artifactId>pagehelper-spring-boot-starter</artifactId>
    <version>1.4.1</version>
</dependency>

3. 多数据源配置

配置多个数据源：

spring:
  datasource:
    primary:
      url: jdbc:mysql://localhost:3306/db1
      username: root
      password: root
      driver-class-name: com.mysql.cj.jdbc.Driver
    secondary:
      url: jdbc:mysql://localhost:3306/DB2
      username: root
      password: root
      driver-class-name: com.mysql.cj.jdbc.Driver

创建配置类：

@Configuration
@MapperScan(basePackages = "com.example.mapper.primary", sqlSessionFactoryRef = "primarySqlSessionFactory")
public class PrimaryDataSourceConfig {
    @Bean(name = "primaryDataSource")
    @ConfigurationProperties(prefix = "spring.datasource.primary")
    public DataSource primaryDataSource() {
        return DataSourceBuilder.create().build();
    }
    @Bean(name = "primarySqlSessionFactory")
    public SqlSessionFactory primarySqlSessionFactory(@Qualifier("primaryDataSource") DataSource dataSource) throws Exception {
        SqlSessionFactoryBean bean = new SqlSessionFactoryBean();
        bean.setDataSource(dataSource);
        bean.setMapperlocations(new PathMatchingResourcePatternResolver().getResources("classpath:mapper/primary/*.xml"));
        return bean.getObject();
    }
    @Bean(name = "primaryTransactionManager")
    public DataSourceTransactionManager primaryTransactionManager(@Qualifier("primaryDataSource") DataSource dataSource) {
        return new DataSourceTransactionManager(dataSource);
    }
}
// 类似地创建SecondaryDataSourceConfig

五、常www.chinasem.cn见问题解决

Mapper接口无法注入：

确保启动类上有@MapperScan("com.example.mapper")注解
或者每个Mapper接口上有@Mapper注解

XML文件找不到：

检查mybatis.mapper-locations配置是否正确
确保XML文件在resources目录下正确位置

驼峰命名不生效：

确认配置mybatis.configuration.map-underscore-to-camel-case=true

连接池配置：

推荐使用Druid连接池，并配置合理的连接参数

事务管理：

在Service方法上添加@Transactional注解

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