java - 不能@autowired 存储库。 Bean 循环引用

Question

我的ApiConfig:

@Configuration
@EnableConfigurationProperties(JpaProperties.class)
@EnableJpaRepositories("com.foo.api.persistence")
@ComponentScan("com.foo.api")
@PropertySource("classpath:application.yaml")
public class ApiConfig {

private static final Logger LOGGER = LogManager.getLogger();
private static final String MODEL_PACKAGE = "com.foo.api.model";

@Autowired
private MultiTenantConnectionProviderImpl multiTenantConnectionProvider;

@Autowired
private ApplicationContext applicationContext;

@Resource
private org.springframework.core.env.Environment env;

@Bean
public LocalContainerEntityManagerFactoryBean entityManagerFactory() throws CurrentTenantIdentifierResolverException {
    LocalContainerEntityManagerFactoryBean entityManagerFactoryBean = new LocalContainerEntityManagerFactoryBean();
    entityManagerFactoryBean.setPackagesToScan(MODEL_PACKAGE);
    entityManagerFactoryBean.setPersistenceProviderClass(HibernatePersistenceProvider.class);

    Properties jpaProperties = new Properties();
    jpaProperties.put(Environment.MULTI_TENANT, MultiTenancyStrategy.SCHEMA);
    jpaProperties.put(Environment.MULTI_TENANT_CONNECTION_PROVIDER, multiTenantConnectionProvider);
    jpaProperties.put(Environment.MULTI_TENANT_IDENTIFIER_RESOLVER, getCurrentTenantIdentifierResolver());
    jpaProperties.put(Environment.DIALECT, getHibernateDialect());

    entityManagerFactoryBean.setJpaProperties(jpaProperties);

    return entityManagerFactoryBean;
}

private CurrentTenantIdentifierResolver getCurrentTenantIdentifierResolver() throws CurrentTenantIdentifierResolverException {
    CurrentTenantIdentifierResolver resolver = applicationContext.getBean(CurrentTenantIdentifierResolver.class);
    if (resolver == null) {
        throw new CurrentTenantIdentifierResolverException();
    }

    return resolver;
}

private String getHibernateDialect() {
    return env.getProperty(PropertyConstants.DIALECT);
}

但现在我不能@Autowired我的JpaRepository:

    @Autowired
    private AgreementPersistence agreementPersistence;

协议(protocol)持久化是简单的 repo 从 JpaRepository 扩展而来，具有自己的基于查询的方法；

异常日志:

Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: 

Could not autowire field: AgreementPersistence agreementPersistence; nested exception is org.springframework.beans.factory.BeanCreationException: 

Error creating bean with name 'agreementPersistence': Cannot create inner bean '(inner bean)#38830ea' of type [org.springframework.orm.jpa.SharedEntityManagerCreator] while setting bean property 'entityManager'; nested exception is org.springframework.beans.factory.BeanCreationException: 

Error creating bean with name '(inner bean)#38830ea': Cannot resolve reference to bean 'entityManagerFactory' while setting constructor argument; nested exception is org.springframework.beans.factory.BeanCurrentlyInCreationException: 

Error creating bean with name 'entityManagerFactory': Requested bean is currently in creation: Is there an unresolvable circular reference?

如何解决？ 也许我可以设置一些 bean 创建顺序或其他东西？

还有: 我需要在另一个模块的配置类中使用@Autowired repo。

Answer 1

循环引用是指您有两个 bean，每个 bean 都注入(inject)到另一个。

@Service
public class A {
    @Inject
    private B b;
}

@Service
public class B {
    @Inject
    private A a;
}

由于 Spring 无法注入(inject)未完全实例化的东西，因此它无法在 B 注入(inject)之前将 A 注入(inject)到 B 中A，反之亦然，从而使 Spring 卡住。

在这些情况下你应该首先分析，看看是否真的需要循环依赖。也许将 bean 分解成这样的东西才是您真正需要的:

@Service
public class C {
    @Inject
    private A a;
    @Inject
    private B b;
}

如果您无法分解解决问题的方法，这是解决问题的一种方法:

@Service
public class A {
    @Inject
    private B b;
}

@Service
public class B extends ApplicationContextAware {
    //no inject
    private A a;

    private ApplicationContext applicationContext;

    public void setApplicationContext(final ApplicationContext applicationContext) throws BeansException {
        this.applicationContext = applicationContext;
    }

    @PostConstruct
    public void handleDependencies() {
        this.a = applicationContext.getBean(A.class);
    }
}