首先添加依赖

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
</dependency>
<dependency>
    <groupId>org.mybatis.spring.boot</groupId>
    <artifactId>mybatis-spring-boot-starter</artifactId>
</dependency>

添加完依赖之后，假设有一个实体类User，其内部存在id、username、password、group四个属性

首先在application.yml内部添加上数据源的信息：

spring:
  datasource:
    url: jdbc:mysql://127.0.0.1:3306/demo_db?useUnicode=true&characterEncoding=utf-8
    username: root
    password: root
    driver-class-name: com.mysql.jdbc.Driver

Mapper类：

package cn.demo.user.mapper;

@Repository
public interface UserMapper{

    @Select("select * from user")
    List<User> findAllUser();

    @Select("select * from user where id = #{id}")
    User findOneUser1(Long id);

    @Select("select * from user where username = #{username} and password = #{password}")
    @Results({
        @Result(property = "id", column = "id"),
        @Result(property = "username", column = "username"),
        @Result(property = "password", column = "password"),
        @Result(property = "group", column = "group")
    })  // 当有多个参数时，注意要加上“@Param”注解，必要时还要添加上“@Results”注解
    User findOneUser2(@Param("username") String username, @Param("password") String password);
}

启动类：注意使用“@MapperScan”注解

@SpringBootApplication
@MapperScan("cn.demo.user.mapper")
public class UserApplication {

    public static void main(String[] args) {
        SpringApplication.run(UserApplication.class, args);
    }
}

此时，就可以在业务层注入UserMapper执行对应的方法了

@Service
public class UserService {

    @Autowired
    private UserMapper userMapper;

    public User findOneUser(String username, String password) {
        return this.userMapper.findOneUser2(username, password);
    }
}

实现动态SQL语句

要实现动态的SQL语句，则需要在原有基础上在创建一个新的动态SQL类

public class UserProvider {

    public String findUserById(Long id) {
        return new SQL() {{
            SELECT("*");
            FROM("user");
            if (id%2 == 1) {
                WHERE("");
            } else {
                WHERE("1=2");
            }
        }}.toString();
    }
}