一、Spring Boot 整合 MyBatis
MyBatis的自动配置
创建工程spring-boot-mybatis，创建项目时勾选MyBatis Framework会自动引入MyBatis的Starter
分析Mybatis的Staters启动器依赖
MyBatis的自动配置类和配置项类都在autoconfigure包下
MyBatis自动配置类依赖了SqlSessionFactory和SqlSessionFactoryBean以及DataSource类，并且启用了MyBatisProperties类中的属性作为配置项，并且在DataSourceAutoConfiguration自动配置类和MybatisLanguageDriverAutoConfiguration类生效后才会生效。
MyBatisProperties类源码中包含了mybatis的配置项
MyBatis的配置前缀都是以mybatis开头
配置Druid数据源
引入driud
代码语言：javascript复制<dependency>
<groupId>com.alibaba</groupId>
<artifactId>druid-spring-boot-starter</artifactId>
<version>1.2.8</version>
</dependency>Druid数据源配置可以参考 Spring 全家桶之 Spring Boot 2.6.4（四）- Data Access（Part A JDBC）
初始化项目
在resources目录下放置employee.sql和department.sql文件
代码语言：javascript复制SET FOREIGN_KEY_CHECKS=0;
-- ----------------------------
-- Table structure for employee
-- ----------------------------
DROP TABLE IF EXISTS `employee`;
CREATE TABLE `employee` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`lastName` varchar(255) DEFAULT NULL,
`email` varchar(255) DEFAULT NULL,
`gender` int(2) DEFAULT NULL,
`d_id` int(11) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8;SET FOREIGN_KEY_CHECKS=0;
-- ----------------------------
-- Table structure for department
-- ----------------------------
DROP TABLE IF EXISTS `department`;
CREATE TABLE `department` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`departmentName` varchar(255) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8;entity目录中创建两个实体类Employee和Department对应employee表和Department表
代码语言：javascript复制@Data
public class Employee {
private Integer id;
private String lastName;
private String email;
private Integer gender;
private Integer dId;
}@Data
public class Department {
private Integer id;
private String departmentName;
}配置自定义数据源初始化类，初始化数据源
代码语言：javascript复制@Configuration
public class LilithDataSourceInitializer {
@Value("classpath:employee.sql")
private Resource employee;
@Value("classpath:department.sql")
private Resource department;
@Bean
public DataSourceInitializer dataSourceInitializer(final DataSource dataSource){
final DataSourceInitializer initializer = new DataSourceInitializer();
initializer.setDataSource(dataSource);
initializer.setDatabasePopulator(databasePopulator());
return initializer;
}
private DatabasePopulator databasePopulator(){
final ResourceDatabasePopulator populator = new ResourceDatabasePopulator();
populator.addScripts(employee,department);
return populator;
}
}启动应用，Spring Boot会自动在数据库表创建，再次启动之前如果不想初始化数据可以将@Configuration注解注释掉
二、MyBatis注解方式的使用
创建DepartmentMapper接口，使用注解标注增删改查的SQL语句
代码语言：javascript复制@Mapper
public interface DepartmentMapper {
@Select("SELECT * FROM department WHERE id = #{id}")
Department selectOneById(Integer id);
@Delete("DELETE FROM department WHERE id = #{id}")
void deleteOneById(Integer id);
@Insert("INSERT INTO department (department_name) VALUES (#{departmentName})")
void insert(Department department);
@Update("UPDATE department SET department_name = #{departmentName} where id = #{departmentId}")
void update(Department department);
}创建DepartmentMapperTest测试类，测试DepartmentMapper中的增删改查方法
代码语言：javascript复制@SpringBootTest
public class DepartmentMapperTest {
@Resource
private DepartmentMapper departmentMapper;
@Test
public void selectOneById() {
Department department = departmentMapper.selectOneById(1);
System.out.println(department);
}
@Test
public void insert() {
Department department = new Department();
department.setDepartmentName("Avengers");
departmentMapper.insert(department);
}
}测试insert方法
测试selectOneById方法
MyBatis 配置驼峰命名转换
修改Department表departmentName为下划线形式department_name；再次执行selectOneById方法
查询到DepartmentName属性为空，这时可以在yml配置文件中开启驼峰命名转换
代码语言：javascript复制mybatis:
configuration:
map-underscore-to-camel-case: true再次查询既可以查询到指定的是数据
配置类开启驼峰命名转换
也可以使用配置类来开启驼峰命名转换，MyBatisAutoConfuguration中包含了configurationCustomizers属性，这是一个List列表，包含了所有的自定义配置
而ConfigurationCustomizer接口中有一个customize方法，该方法传入Configuration自定义配置
Configuration类中的属性就是可以自定义的配置
在config包下新建LilithMyBatisConfig配置类，新增一个configurationCustomizer方法，既往容器中注入ConfigurationCustomizer设置了属性的实现类
代码语言：javascript复制@Configuration
public class LilithMyBatisConfig {
@Bean
public ConfigurationCustomizer configurationCustomizer(){
return configuration -> configuration.setMapUnderscoreToCamelCase(true);
}
}这里使用lambda表达式实现了ConfigurationCustomizer接口中的customize方法
将yml文件中的驼峰命名转换注释，重新执行selectOneById方法
可以成功查询出数据。
@Mapper注解
@Mapper注解是自动配置的关键，标记当前类为容器的一个组件，缺少@Mapper注解将无法启动。
当Mapper接口非常多是，给每一个Mapper接口增加@Mapper注解非常麻烦，可以在主启动类上使用@MapperScan注解，扫描所有的Mapper接口
三、MyBatis配置文件方式的使用
创建Mapper接口EmployeeMapper，需要说明的是无论是注解还是配置文件方式使用MyBatis，@Mapper注解或者@MapperScan注解都是必不可少的。
代码语言：javascript复制@Mapper
public interface EmployeeMapper {
void insert(Employee employee);
Employee selectOneById(Integer id);
}在resources目录下创建mappers文件夹，新增EmployeeMapper.xml文件，增加Mapper接口中selectOneById方法和insert方法对应的SQL语句
代码语言：javascript复制<?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.lilith.mybatis.mapper.EmployeeMapper">
<select id="selectOneById" resultType="com.lilith.mybatis.entity.Employee">
select * from employee where id = #{id}
</select>
<insert id="insert" useGeneratedKeys="true" keyProperty="id" keyColumn="id">
INSERT INTO employee (last_name, email, gender, d_id)
VALUES (#{lastName}, #{email}, #{gender},#{dId})
</insert>
</mapper>yml中增加mybatis配置
代码语言：javascript复制mybatis:
# 全局配置文件的位置
config-location: classpath:mybatis-config.xml
mapper-locations: classpath:mappers/*.xml
configuration:
map-underscore-to-camel-case: true书写测试类
代码语言：javascript复制@SpringBootTest
public class EmployeeMapperTest {
@Resource
private EmployeeMapper employeeMapper;
@Test
public void insert() {
Employee employee = new Employee();
employee.setLastName("Thanos");
employee.setEmail("thanos@gmail.com");
employee.setGender(1);
employee.setDId(1);
employeeMapper.insert(employee);
}
@Test
public void selectOneById() {
Employee employee = employeeMapper.selectOneById(1);
System.out.println(employee);
}
}执行插入方法
错误提示config-location和configuration不能同时写在yml文件中； 在resources目录下新建MyBatis全局配置文件，把configuration配置到mybatis-config.xml全局配置文件中
代码语言：javascript复制<?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>再次执行测试
控制台显示有1行成功更新，数据被成功插入到输入句酷表中
执行selectOneById方法
成功查询出insert方法插入的数据
