先上https://start.spring.io/上創(chuàng)建項目，添加mysql,mybatis依賴，maven文件如下：

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.4.4</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.zdt</groupId>
    <artifactId>demo</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>demo</name>
    <description>Demo project for Spring Boot</description>
    <properties>
        <java.version>1.8</java.version>
    </properties>
    <dependencies>      
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.mybatis.spring.boot</groupId>
            <artifactId>mybatis-spring-boot-starter</artifactId>
            <version>2.1.4</version>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

yml配置文件，設置數(shù)據(jù)源和mybatis

spring:
  datasource:
    username: root
    password: 123456
    url: jdbc:mysql://localhost:3306/test?useUnicode=true&characterEncoding=utf-8&useSSL=true&serverTimezone=UTC
    driver-class-name: com.mysql.jdbc.Driver

mybatis:
  mapper-locations: classpath:mapper/*Mapper.xml

在mysql 中創(chuàng)建一張user 表，包含id,name,age字段

CREATE TABLE `user` (
  `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `name` varchar(200) NOT NULL,
  `age` int(10) NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=2 DEFAULT CHARSET=utf8;

創(chuàng)建mapper,service,service.impl,pojo,controller幾個包
必須在啟動的application類上加上掃描mapper的注解,否則會找不到mapper

@SpringBootApplication
@MapperScan(basePackages = "com.zdt.demo.mapper")
public class DemoApplication {
    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
    }
}

在pojo包下創(chuàng)建User,最好是沒有構造函數(shù)，否則會報錯，原因暫切不明。

public class User {
    private Long id;
    private String name;
    private Integer age;

//    public User(String name,int age){
//        this.name=name;
//        this.age=age;
//    }

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }
}

在mapper包下創(chuàng)建UserMapper來直接訪問數(shù)據(jù)庫,加上mapper注解

@Mapper
public interface UserMapper extends Mapper {
    @Select("select * from user where id = #{id}")
    public User getUser(Long id );
}

service包下創(chuàng)建UserService接口

public interface UserService {
    public User getUserById(Long id);
}

impl下創(chuàng)建UserServiceImpl實現(xiàn)UserService接口,加上service 注解 并注入userMapper

@Service
public class UserServiceImpl implements UserService {
    @Autowired
    private UserMapper userMapper;
    @Override
    public User getUserById(Long id) {
        return userMapper.getUser(id);
    }
}

最后就可以在控制器中調用userService中的getUserByid來獲取用戶數(shù)據(jù)了，請事先在數(shù)據(jù)庫添加一下相應的記錄

@RestController
public class Hello {
    @Autowired
    private UserService userService;

    @GetMapping("/hello")
    public User index(){
        return userService.getUserById(1l);
    }
}

瀏覽器訪問http://localhost:8080/hello 就可以查看到用戶記錄了。
如果要使用XML來配置mapper,則配置中要增加mapper的xml路徑：

mybatis:
  mapper-locations: classpath:mapper/*Mapper.xml
  type-aliases-package: com.zdt.demo.pojo

在資源文件夾中創(chuàng)建mapper文件夾，并創(chuàng)建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.zdt.demo.mapper.UserMapper">
    <select id="findAll" resultType="User">
        SELECT * FROM user
    </select>
    <select id="getUserById" resultType="com.zdt.demo.pojo.User" >
        SELECT * FROM user WHERE id=#{id}
    </select>
</mapper>

mapper中增加 新的方法

@Mapper
public interface UserMapper extends Mapper {
    public User getUserById(Long id);
    public List<User> findAll();
}

然后service 中就可以調用新增的方法了。