java - 请求的 bean 当前正在创建中

Question

我的 Controller

@RestController
public class CheckUserDataRestController {
    private final UserSearchService userSearchService;
    @Autowired
    public CheckUserDataRestController(final UserSearchService userSearchService) {
        this.userSearchService = userSearchService;
    }
...
}

初始化bean服务

@Service("userSearchService")
public class UserSearchServiceImpl implements UserSearchService {
    private final UserRepository userRepository;
    private final AuthorizationService authorizationService;
    @Autowired
    public UserSearchServiceImpl(
            @NotNull final UserRepository userRepository,
            @NotNull final AuthorizationService authorizationService
    ) {
        this.userRepository = userRepository;
        this.authorizationService = authorizationService;
    }
...
}

初始化另一个服务bean

@Service("authorizationService")
public class AuthorizationServiceImpl implements AuthorizationService {
    private final UserSearchService userSearchService;
    @Autowired
    public AuthorizationServiceImpl(final UserSearchService userSearchService) {
        this.userSearchService = userSearchService;
    }
...
}

编译时抛出如下错误:

2018-04-05 02:09:39.024  WARN 1864 --- [           main] ConfigServletWebServerApplicationContext : Exception encountered during context initialization - cancelling refresh attempt: org.springframework.beans.factory.UnsatisfiedDependencyException: 
Error creating bean with name 'checkUserDataRestController' defined in file [C:\Users\Jonatan\Documents\GitHub\REST-Web-Services\web\out\production\classes\com\web\web\controller\CheckUserDataRestController.class]: Unsatisfied dependency expressed through constructor parameter 0; nested exception is org.springframework.beans.factory.UnsatisfiedDependencyException: 
Error creating bean with name 'userSearchService' defined in file [C:\Users\Jonatan\Documents\GitHub\REST-Web-Services\core\out\production\classes\com\core\jpa\service\UserSearchServiceImpl.class]: Unsatisfied dependency expressed through constructor parameter 1; nested exception is org.springframework.beans.factory.UnsatisfiedDependencyException: 
Error creating bean with name 'authorizationService' defined in file [C:\Users\Jonatan\Documents\GitHub\REST-Web-Services\core\out\production\classes\com\core\service\impl\AuthorizationServiceImpl.class]: Unsatisfied dependency expressed through constructor parameter 0; nested exception is org.springframework.beans.factory.BeanCurrentlyInCreationException: 
Error creating bean with name 'userSearchService': Requested bean is currently in creation: Is there an unresolvable circular reference?

该错误是由于 UserSearchService 服务在 Controller 和 AuthorizationService 服务中同时 Autowiring 造成的。如何防止此错误？

Answer 1

问题在于 AuthorizationServiceImpl 的构造函数需要连接 UserSearchService 的 bean，这意味着 UserSearchServiceImpl 将被连接，但是UserSearchServiceImpl 的构造函数需要连接 AuthorizationServiceImpl 的 bean(这意味着将连接 AuthorizationServiceImpl)。这种依赖是循环的，如果没有开发人员的帮助，Spring 无法解决它:

AuthorizationServiceImpl → UserSearchServiceImpl → AuthorizationServiceImpl

打破这种循环依赖的一种方法是通过setter injection 将UserSearchService bean 注入(inject)到AuthorizationServiceImpl 中。 , 而不是通过 constructor injection .这允许 Spring 创建 AuthorizationServiceImpl bean 而无需创建 UserSearchServiceImpl bean。一旦初始化了 AuthorizationServiceImpl，就可以初始化 UserSearchServiceImpl bean。一旦 UserSearchServiceImpl 被初始化，它就可以使用它的 setter 连接到 AuthorizationServiceImpl 中。这减少了对以下内容的依赖:

UserSearchServiceImpl → AuthorizationServiceImpl

为此，将 AuthorizationServiceImpl 更改为以下内容:

@Service("authorizationService")
public class AuthorizationServiceImpl implements AuthorizationService {
    private UserSearchService userSearchService;

    public AuthorizationServiceImpl() {}

    @Autowired
    public void setUserSearchService(UserSearchService userSearchService) {
        this.userSearchService = userSearchService;
    }

    ...

}

和 UserSearchServiceImpl 到以下内容:

@Service("userSearchService")
public class UserSearchServiceImpl implements UserSearchService {

    private final UserRepository userRepository;
    private AuthorizationService authorizationService;

    @Autowired
    public UserSearchServiceImpl(@NotNull final UserRepository userRepository) {
        this.userRepository = userRepository;
    }

    @Autowired
    public void setAuthorizationService(AuthorizationService authorizationService) {
        this.authorizationService = authorizationService;
    }

    ...
}

重要的是要注意，技术要求 userSearchService 和 authorizationService 字段可变(删除 final 限定符)。