一、添加mybatis-plus相关依赖

<dependency>
    <groupId>com.baomidou</groupId>
    <artifactId>mybatis-plus-boot-starter</artifactId>
    <version>3.3.0</version>
</dependency>
<dependency>
    <groupId>com.baomidou</groupId>
    <artifactId>mybatis-plus-generator</artifactId>
    <version>3.3.0</version>
</dependency>
<dependency>
    <groupId>com.baomidou</groupId>
    <artifactId>dynamic-datasource-spring-boot-starter</artifactId>
    <version>3.0.0</version>
</dependency>

二、设置数据源配置

spring:
  application:
    name: rtt
  datasource:
    dynamic:
      primary: master
      datasource:
        master: 
          url: jdbc:mysql://192.168.0.1:3306/datasync?&useUnicode=true&characterEncoding=utf8&serverTimezone=CTT
          username: mysql
          password: mysql
          driver-class-name: com.mysql.cj.jdbc.Driver
        slave_1:
          url: jdbc:mysql://192.168.0.2:3306/datasync?&useUnicode=true&characterEncoding=utf8&serverTimezone=CTT
          username: mysql
          password: mysql
          driver-class-name: com.mysql.cj.jdbc.Driver
        slave_2:
          url: jdbc:mysql://192.168.0.3:3306/datasync?&useUnicode=true&characterEncoding=utf8&serverTimezone=CTT
          username: mysql
          password: mysql
          driver-class-name: com.mysql.cj.jdbc.Driver

master为主库，负责增删改；slave_1、slave_2为从库，负责查询。

三、编写mybatis-plus配置类

@Configuration
@EnableTransactionManagement
@MapperScan("com.zq.datasync.mapper")
public class MybatisPlusConfig {
    /**
     * 分页配置
     * @return
     */
    @Bean
    public PaginationInterceptor paginationInterceptor(){
        return new PaginationInterceptor();
    }

    /**
     * 乐观锁配置
     * @return
     */
    @Bean
    public OptimisticLockerInterceptor optimisticLockerInterceptor() {
        return new OptimisticLockerInterceptor();
    }

    /**
     * 读写分离配置
     * @return
     */
    @Bean
    public MasterSlaveAutoRoutingPlugin masterSlaveAutoRoutingPlugin() {
        return new MasterSlaveAutoRoutingPlugin();
    }
}

四、测试

@RestController
@RequestMapping("/person")
public class PersonController {
    @Autowired
    private IPersonService personService;

    @PostMapping("save")
    public ResponseResult add(@RequestBody Person person) {
        personService.save(person);
        return ResponseResultUtil.success();
    }

    @PutMapping("update")
    public ResponseResult update(@RequestBody Person person) {
        Person o = personService.getById(person.getId());
        if (o != null) {
            BeanCopyUtil.copyPropertiesIgnoreNull(person, o);
            personService.updateById(o);
        }
        return ResponseResultUtil.success();
    }

    @DeleteMapping("delete/{id}")
    public ResponseResult delete(@PathVariable Long id) {
        personService.removeById(id);
        return ResponseResultUtil.success();
    }

    @GetMapping("list")
    @DS("slave")
    public ResponseResult list() {
        return ResponseResultUtil.success(personService.list());
    }
}

当调用/person/save、/person/update、/person/delete/1接口时，操作的是master数据库；当调用/person/list接口时，轮训操作slave_1、slave_2数据库。