SpringBoot整合Mybatis

1、注解方式
（1）注解方式用接口+注解（@Mapper）方式实现Mybatis操作数据库

@Mapper
public interface DepartmentMapper {
    @Select("select * from department where id=#{id}")
    public Department getDeptById(Integer id);

    @Delete("delete from department where id=#{id}")
    public int deleteDeptById(Integer id);

    @Insert("insert into department(id,departmentName) values(#{id},#{departmentName})")
    public int insertDept(Department department);

    @Update("update department set departmentName=#{departmentName} where id=#{id}")
    public int updateDept(Department department);
}

注：如果Mapper接口非常多且都位于相同包下，可以再SpringBoot主配置类或者Mybatis配置类上添加@MapperScan(value = "com.chen.springboot.mapper")等同于对包下所有接口添加@Mapper注解
（2）controller类可以直接通过@Autowired容器接口来调用其中方法来执行相应的sql语句

@RestController
public class DepartmentController {
    @Autowired
    DepartmentMapper departmentMapper;
    @GetMapping("/dept/{id}")
    public Department getDepartment(@PathVariable("id") Integer id){
        return departmentMapper.getDeptById(id);
    }
    @GetMapping("/dept")
    public Department insertDept(Department department){
        departmentMapper.insertDept(department);
        return department;
    }
}

2、xml配置文件方式
（1）创建操作数据库的接口及其方法

public interface EmployeeMapper {

    public Employee getEmpById(Integer id);

    public void insertEmp(Employee employee);
}

（2）编写Mybatis配置文件（Mybatis配置文件全面托管于Github上，可以去Github的Mybatis的使用文档来查看配置文件规范）


进入Getting Started有详细的Mybatis配置过程

言归正传，继续我们的Mybatis配置文件（mybatis-config.xml）：

<?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></configuration>

Mapper映射文件（EmployeeMapper.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.chen.springboot.mappper.EmployeeMapper">
    <select id="getEmpById" resultType="com.chen.springboot.bean.Employee">
        select * from employee where id=#{id}
    </select>
    <insert id="insertEmp">
        insert into employee(id,lastName,email,gender,d_id) values(#{id},#{lastName},#{email},#{gender},#{dId})
    </insert>
</mapper>

最后在SpringBoot配置文件（application.yml）中将Mapper配置文件和Mybatis配置文件整合并在SpringBoot中生效：

mybatis:
  config-location: classpath:mybatis/mybatis-config.xml
  mapper-locations: classpath:mybatis/mapper/*.xml

（3）controller类可以直接通过@Autowired容器接口来调用其中方法来执行相应的sql语句

@RestController
public class EmployeeController {
    @Autowired
    EmployeeMapper employeeMapper;
    @GetMapping("/emp/{id}")
    public Employee getEmpById(@PathVariable("id")Integer id){
        return employeeMapper.getEmpById(id);
    }
    @GetMapping("/emp")
    public Employee insertEmp(Employee employee){
        employeeMapper.insertEmp(employee);
        return employee;
    }
}

3、总结springboot开启mybatis驼峰命名自动映射的三种方式
方式一：通过springboot的配置文件（application.yml）：

mybatis:
  configuration:
    map-underscore-to-camel-case: true

此方式是最简单的，但是要注意，通过springboot的配置文件配置mybatis的设置，则不能够再使用mybatis的配置文件，例如：下边代码中①②的两个设置不能同时存在，要么使用config-location指定mybatis的配置文件，在通过mybatis的配置文件配置相关设置，要么通过springboot配置文件的mybatis.configuration进行相关设置，二者只能选其一，否则会报错。

mybatis:
  config-location: classpath:mybatis/mybatis-config.xml ①
  mapper-locations: classpath:mybatis/mapper/*.xml
  configuration:
    map-underscore-to-camel-case: true ②

方式二：通过mybatis的配置文件
首先需要在springboot的配置文件application.yml中指定mybatis配置文件的位置。

mybatis:
  config-location: classpath:mybatis/mybatis-config.xml
  mapper-locations: classpath:mybatis/mapper/*.xml

然后在mybatis配置文件中进行设置

<?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>
   <settings>
       <setting name="mapUnderscoreToCamelCase" value="true"/>
    </settings>
</configuration>

方式三：通过@Comfiguration注解和@Bean注解，向容器中添加ConfigurationCustomizer类型的组件，在ConfigurationCustomizer中进行设置

@Configuration
public class MybatisConfig {
    @Bean
    public ConfigurationCustomizer configurationCustomizer(){
        return new ConfigurationCustomizer() {
            @Override
            public void customize(org.apache.ibatis.session.Configuration configuration) {
                configuration.setMapUnderscoreToCamelCase(true);
            }
        };
    }
}