SpringBoot:如何访问java类@Autowired中的存储库不工作
Spring Boot:如何访问java class@Autowired不工作中的存储库 请用示例代码解释您的解决方案,因为我是Spring Boot新手 存储库SpringBoot:如何访问java类@Autowired中的存储库不工作,spring,spring-boot,spring-data-jpa,Spring,Spring Boot,Spring Data Jpa,Spring Boot:如何访问java class@Autowired不工作中的存储库 请用示例代码解释您的解决方案,因为我是Spring Boot新手 存储库 import java.util.List; import org.springframework.data.repository.CrudRepository; public interface StoreRepository extends CrudRepository<Store, Integer> {
import java.util.List;
import org.springframework.data.repository.CrudRepository;
public interface StoreRepository extends CrudRepository<Store, Integer> {
List<Store> findAll();
}
**商店服务**
import java.util.List;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
@Service
public class StoreService {
@Autowired
private StoreRepository storeRepository;
public StoreService() {
}
public List<Stores> getAllStores(){
return (List<Stores>) storeRepository.findAll(); /* This works good. Through controller I can retrieve all data*/
}
}
错误:
Exception in thread "StoreWorker : restartedMain" java.lang.reflect.InvocationTargetException
Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name
Caused by: org.springframework.beans.BeanInstantiationException: Failed to instantiate [io.store.workers.StoreWorker]: Constructor threw exception; nested exception is java.lang.NullPointerException
Caused by: java.lang.NullPointerException
请用示例代码解释您的解决方案,因为我是Spring Boot新手。您应该在构造函数级别使用@Autowire,以便在构造函数内部使用Autowire变量
@Component
public class StoreWorker {
@Autowired
public StoreWorker(StoreRepository storeRepository) {
System.out.println(storeRepository.findAll());
}
(或)使用后期施工
在构造对象之后发生。因此,在构造函数完成之前不会设置它们
如果您需要运行一些初始化代码,您应该能够将构造函数中的代码拉入一个方法,并用@PostConstruct注释该方法。您必须以以下方式更改代码: 如果您想在类的构造函数中使用自连线bean,请使用构造函数注入。这也是最推荐的注射方式
@Component
public class StoreWorker {
private final StoreRepository storeRepository;
public StoreWorker(StoreRepository storeRepository) {
this.storeRepository = storeRepository;
System.out.println(storeRepository.findAll());
}
}
因此,当
StoreWorker
被实例化时,自动连线beanstoreRepository
被注入。由于发生这种情况,您可以使用storeRepository
bean。您不应该在构造函数中放入任何逻辑。构造函数方法仅用于初始化实例。
使用单独的方法调用storeRepository
@Component
public class StoreWorker {
@Autowired
private StoreRepository storeRepository;
public void findAll() {
System.out.println(storeRepository.findAll());
}
}
Spring调用构造函数时,上下文未完全初始化,并且由于未使用构造函数注入,storeRepository
尚未注入
构造函数注入是Spring团队推荐的注入方式。从Spring4.3开始,您甚至不需要在构造函数上添加@Autowired
注释
@Component
public class StoreWorker {
private StoreRepository storeRepository;
//@Autowired not needed since v4.3
public StoreWorker(StoreRepository storeRepository) {
this.storeRepository = storeRepository;
}
...
}
如果您想依靠其他外部bean对bean进行进一步初始化,请使用带有@PostConstruct
注释的单独方法进行初始化
@Component
public class StoreWorker {
private StoreRepository storeRepository;
private List<Store> stores;
public StoreWorker(StoreRepository storeRepository) {
this.storeRepository = storeRepository;
}
@PostConstruct
public void initializeMyBean() {
stores = storeRepository.findAll();
}
}
@组件
公营仓库工人{
私有存储库存储库;
私人名单商店;
公共存储工人(存储库存储库){
this.storeRepository=storeRepository;
}
@施工后
public void initializeMyBean(){
stores=storeRepository.findAll();
}
}
尝试使用存储库注释和组件still,我得到System.out.println(storeRepository);=各位,发表评论,然后对答案进行否决投票,这样,如果我的答案有任何缺陷,我就可以纠正它。简单地对答案投否决票会伤害其他人,它会停止回答stackover flow中的其他问题。@Repository
扩展org.springframework.data.Repository.Repository
interface@Matt谢谢你的评论。但提及存储库不会损害类,但也没关系。虽然我在回答的第二部分已经回答了这个问题。你可以编辑答案,而不是投反对票,对吗?这毁了我的周末,你凭什么认为我否决了你的答案?我只是在发表评论
@Component
public class StoreWorker {
private StoreRepository storeRepository;
//@Autowired not needed since v4.3
public StoreWorker(StoreRepository storeRepository) {
this.storeRepository = storeRepository;
}
...
}
@Component
public class StoreWorker {
private StoreRepository storeRepository;
private List<Store> stores;
public StoreWorker(StoreRepository storeRepository) {
this.storeRepository = storeRepository;
}
@PostConstruct
public void initializeMyBean() {
stores = storeRepository.findAll();
}
}