java - SpringBoot : Unsatisfied dependency NoSuchBeanDefinitionException, 期望至少有 1 个有资格作为 Autowiring 候选者的 bean

Question

我犯了一个非常愚蠢的错误，但不知道如何修复。

我有一个使用配置文件的简单 SpringBoot 应用程序，它连接到 MongoDb。

我的pom.xml依赖项:

<parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>2.1.3.RELEASE</version>
</parent>
<dependencies>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-test</artifactId>
    </dependency>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-data-mongodb</artifactId>
    </dependency>
</dependencies>

我的StudentController.java

@RestController
@RequestMapping("/students")
public class StudentController {

    @Autowired
    private StudentService studentService;

    @RequestMapping(method = RequestMethod.GET)
    public Collection<Student> getAllStudents(){
        return studentService.getAllStudents();
    }
}

我的StudentService.java

@Service
public class StudentService {

    @Autowired
    private StudentDao studentDao;

    public Collection<Student> getAllStudents(){
        return this.studentDao.getAllStudents();
    }
}

我的StudentDao.java接口(interface):

public interface StudentDao {
    Collection<Student> getAllStudents();
}

我的MongoStudentDaoImpl.java:

@Repository
@Profile("test")
public class MongoStudentDaoImpl implements StudentDao {

    @Autowired
    private MongoStudentRepo repo;

    @Override
    public Collection<Student> getAllStudents() {
        return repo.findAll();
    }
}

我的MongoStudentRepo.java:

@Profile("test")
public interface MongoStudentRepo extends MongoRepository<Student, String> {
}

当我尝试使用“测试”配置文件启动应用程序时，这是我看到的错误:

Exception encountered during context initialization - cancelling refresh attempt: org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'studentController': Unsatisfied dependency expressed through field 'studentService'; nested exception is org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'studentService': Unsatisfied dependency expressed through field 'studentDao'; nested exception is org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'mongoStudentDaoImpl': Unsatisfied dependency expressed through field 'repo'; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type 'MongoStudentRepo' available: expected at least 1 bean which qualifies as autowire candidate. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}

我在这里缺少什么？我需要向 MongoStudentRepo.java 添加注释吗？

提前致谢。

Answer 1

堆栈跟踪显示 spring 无法 Autowiring MongoStudentDaoImpl.java 类中的 bean MongoStudentRepo 之一。来自堆栈跟踪:

 Unsatisfied dependency expressed through field 'repo'; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type 'MongoStudentRepo' available: expected at least 1 bean which qualifies as autowire candidate. Dependency annotations: 

Spring 抛出此异常意味着 MongoStudentRepo.class 的 bean 未正确创建。

可能的解决方案:

• 问题可能是因为 spring 没有使用 spring 中的默认实现为您的接口(interface)创建 bean。这可能是因为您没有使用注释 @EnableJpaRepositories 来启用默认的扫描和创建存储库 bean。有关更多信息，请阅读 here.

但是如果您使用基于 xml 的配置，对于基于 xml 的配置使用:

<repositories base-package="com.acme.repository" />

<repositories base-package="com.acme.repository" repository-impl-postfix="MyPostfix" />

或者使用@Configuration注释:

@Configuration
@EnableJpaRepositories("com.acme.repositories")
class ApplicationConfiguration {

  @Bean
  EntityManagerFactory entityManagerFactory() {
    // …
  }
}

当您使用 spring 默认实现时，您只能为“测试”配置文件加载此配置。

最佳阅读:https://docs.spring.io/spring-data/mongodb/docs/current/reference/html/#repositories.custom-implementations