java - Spring Boot 中的循环依赖

Question

我试图在我的 bootspring 项目中使用restTemplate，当我编译时出现如下错误:

There is a circular dependency between 4 beans in the application context:
- courseController (field com.example.service.CourseService com.example.controller.CourseController.courseDAO)
- courseServiceRest (field private com.example.dao.CourseDAO com.example.service.CourseServiceRest.courseDAO)
- courseDAOImpl (field private org.springframework.web.client.RestTemplate com.example.dao.CourseDAOImpl.restTemplate)
- studentDAOImpl (field private org.springframework.web.client.RestTemplate com.example.dao.StudentDAOImpl.restTemplate)
- restTemplate

下面是我的代码:

我想是因为我在StudenDAOImpl和CourseDAOImpl中有相同的@bean，因为如果我删除CourseDAOImpl编译成功，代码如下:

StudentDAOImpl 代码:

@Service
public class StudentDAOImpl implements StudentDAO
{
    @Autowired
    private RestTemplate restTemplate;

    @Bean
    public RestTemplate restTemplate(RestTemplateBuilder builder) {
       return builder.build();
    }

    @Override
    public StudentModel selectStudent (String npm)
    {
        StudentModel student = restTemplate.getForObject(url+npm, StudentModel.class);
        return student;
    }

    @Override
    public List<StudentModel> selectAllStudents ()
    {
       return null;
    }

}

CourseDAOImpl 代码:

@Service
public class CourseDAOImpl implements CourseDAO {

    @Autowired
    private RestTemplate restTemplate;

    @Bean
    public RestTemplate restTemplate(RestTemplateBuilder builder) {
        return builder.build();
    }

    @Override
    public CourseModel selectCourse(String id) {
        CourseModel course = restTemplate.getForObject(urlCourse+id, CourseModel.class);
        return course;
    }

    @Override
    public List<CourseModel> selectAllCourses() {   
        return null;    
    }
}

有答案吗？非常感谢。

Answer 1

问题出在您的 DAO 中，您应该删除 @Bean 配置，并让每个 DAO 的配置如下所示

@Service
public class StudentDAOImpl implements StudentDAO
{
    @Autowired
    private RestTemplate restTemplate;

    @Override
    public StudentModel selectStudent (String npm)
    {
        StudentModel student = restTemplate.getForObject(url+npm, StudentModel.class);
        return student;
    }

    @Override
    public List<StudentModel> selectAllStudents ()
    {
       return null;
    }

}

然后在配置 Bean 或入口点应用程序中，您可以添加restTemplate bean。例如这里是 Config.java 中的一个配置 Bean

@Configuration
public class Config {
     @Bean
     public RestTemplate restTemplate(RestTemplateBuilder builder) {
       return builder.build();
     }
}