使用Spring，JPA和Hibernate的通用DAO設置

Question

我正在嘗試編寫一個通用代碼，以在任何實體上實現一些最常見的操作。 我已經使用Spring Initializr使用Gradle，Spring Boot 2.1.0 SNAPSHOT，JPA和Hibernate來生成產品的基礎。 我使用MySQL Workbench創建了架構和表，並使用它們為我的項目生成了實體。 因此，針對實際問題，我嘗試創建一個通用的DAO，在其中將實現一些常見的操作（例如findbyid，edit，delete，create，update，getall），然后將其擴展到其他DAO類以促進可重用性並進行工作。快點。 所以這是我到目前為止的代碼：

UserController.java ：

@RestController
public class UserController {

    @Autowired
    UserService userService;

    @RequestMapping(value = "/getUser", method = RequestMethod.GET)
    @ResponseBody
    public UserEntity getUser() throws Exception {
        userService.getUser();
    }
}

UserService.java ：

public interface UserService {
    UsersEntity getUser();
}

UserServiceImpl.java ：

@Service
public class UserServiceImpl implements UserService {

    @Autowired
    UserDAO userDAO;

    @Transactional
    public UsersEntity getUser() {
        return userDAO.find(Long.valueOf("123"));
    }
}

UserDAO.java ：

public interface UserDAO extends GenericRepositoryInterface<UsersEntity> {
}

UserDAOImpl.java ：

@Repository
public abstract class UserDAOImpl implements UserDAO {
}

GenericRepositoryInterface.java ：

public interface GenericRepositoryInterface<T> {
    T save(T emp);
    Boolean delete(T emp);
    T edit(T emp);
    T find(Long empId);
}

GenericRepositoryImplementation.java ：

@Repository
public class GenericRepositoryImplementation<T> implements GenericRepositoryInterface<T> {

    protected EntityManager entityManager;
    private T type;

    public GenericRepositoryImplementation(T type) {
        // TODO Auto-generated constructor stub
        this.type = type;
    }

    public EntityManager getEntityManager() {
        return entityManager;
    }

    @PersistenceContext
    public void setEntityManager(EntityManager entityManager) {
        this.entityManager = entityManager;
    }

    @Override
    public T save(T emp) {
        // TODO Auto-generated method stub
        entityManager.persist(emp);
        entityManager.flush();
        return emp;
    }

    @Override
    public Boolean delete(T emp) {
        // TODO Auto-generated method stub
        try {
            entityManager.remove(emp);
        } catch (Exception ex) {
            return false;
        }
        return true;
    }

    @Override
    public T edit(T emp) {
        // TODO Auto-generated method stub
        try{
            return entityManager.merge(emp);
        } catch(Exception ex) {
            return null;
        }
    }

    @Override
    public T find(Long empId) {
        // TODO Auto-generated method stub
        return (T) entityManager.find(type.getClass(), empId);
    }
}

我不確定實現的地方在哪里，但是每當我運行應用程序時，它都會崩潰並顯示以下日志：

2018-06-24 18:12:14.748 DEBUG 72491 --- [  restartedMain] o.s.b.d.LoggingFailureAnalysisReporter   : Application failed to start due to an exception

        org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type 'com.example.test.dao.UserDAO' available: expected at least 1 bean which qualifies as autowire candidate. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}
        at org.springframework.beans.factory.support.DefaultListableBeanFactory.raiseNoMatchingBeanFound(DefaultListableBeanFactory.java:1509) ~[spring-beans-5.1.0.BUILD-SNAPSHOT.jar:5.1.0.BUILD-SNAPSHOT]
        at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1104) ~[spring-beans-5.1.0.BUILD-SNAPSHOT.jar:5.1.0.BUILD-SNAPSHOT]
        at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1065) ~[spring-beans-5.1.0.BUILD-SNAPSHOT.jar:5.1.0.BUILD-SNAPSHOT]
        at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:584) ~[spring-beans-5.1.0.BUILD-SNAPSHOT.jar:5.1.0.BUILD-SNAPSHOT]
        at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:91) ~[spring-beans-5.1.0.BUILD-SNAPSHOT.jar:5.1.0.BUILD-SNAPSHOT]
        at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:373) ~[spring-beans-5.1.0.BUILD-SNAPSHOT.jar:5.1.0.BUILD-SNAPSHOT]
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1350) ~[spring-beans-5.1.0.BUILD-SNAPSHOT.jar:5.1.0.BUILD-SNAPSHOT]
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:580) ~[spring-beans-5.1.0.BUILD-SNAPSHOT.jar:5.1.0.BUILD-SNAPSHOT]
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:503) ~[spring-beans-5.1.0.BUILD-SNAPSHOT.jar:5.1.0.BUILD-SNAPSHOT]
        at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:317) ~[spring-beans-5.1.0.BUILD-SNAPSHOT.jar:5.1.0.BUILD-SNAPSHOT]
        at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222) ~[spring-beans-5.1.0.BUILD-SNAPSHOT.jar:5.1.0.BUILD-SNAPSHOT]
        at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:315) ~[spring-beans-5.1.0.BUILD-SNAPSHOT.jar:5.1.0.BUILD-SNAPSHOT]
        at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199) ~[spring-beans-5.1.0.BUILD-SNAPSHOT.jar:5.1.0.BUILD-SNAPSHOT]
        at org.springframework.beans.factory.config.DependencyDescriptor.resolveCandidate(DependencyDescriptor.java:251) ~[spring-beans-5.1.0.BUILD-SNAPSHOT.jar:5.1.0.BUILD-SNAPSHOT]
        at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1138) ~[spring-beans-5.1.0.BUILD-SNAPSHOT.jar:5.1.0.BUILD-SNAPSHOT]
        at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1065) ~[spring-beans-5.1.0.BUILD-SNAPSHOT.jar:5.1.0.BUILD-SNAPSHOT]
        at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:584) ~[spring-beans-5.1.0.BUILD-SNAPSHOT.jar:5.1.0.BUILD-SNAPSHOT]
        at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:91) ~[spring-beans-5.1.0.BUILD-SNAPSHOT.jar:5.1.0.BUILD-SNAPSHOT]
        at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:373) ~[spring-beans-5.1.0.BUILD-SNAPSHOT.jar:5.1.0.BUILD-SNAPSHOT]
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1350) ~[spring-beans-5.1.0.BUILD-SNAPSHOT.jar:5.1.0.BUILD-SNAPSHOT]
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:580) ~[spring-beans-5.1.0.BUILD-SNAPSHOT.jar:5.1.0.BUILD-SNAPSHOT]
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:503) ~[spring-beans-5.1.0.BUILD-SNAPSHOT.jar:5.1.0.BUILD-SNAPSHOT]
        at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:317) ~[spring-beans-5.1.0.BUILD-SNAPSHOT.jar:5.1.0.BUILD-SNAPSHOT]
        at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222) ~[spring-beans-5.1.0.BUILD-SNAPSHOT.jar:5.1.0.BUILD-SNAPSHOT]
        at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:315) ~[spring-beans-5.1.0.BUILD-SNAPSHOT.jar:5.1.0.BUILD-SNAPSHOT]
        at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199) ~[spring-beans-5.1.0.BUILD-SNAPSHOT.jar:5.1.0.BUILD-SNAPSHOT]
        at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:760) ~[spring-beans-5.1.0.BUILD-SNAPSHOT.jar:5.1.0.BUILD-SNAPSHOT]
        at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:869) ~[spring-context-5.1.0.BUILD-SNAPSHOT.jar:5.1.0.BUILD-SNAPSHOT]
        at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:550) ~[spring-context-5.1.0.BUILD-SNAPSHOT.jar:5.1.0.BUILD-SNAPSHOT]
        at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:140) ~[spring-boot-2.1.0.BUILD-SNAPSHOT.jar:2.1.0.BUILD-SNAPSHOT]
        at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:762) [spring-boot-2.1.0.BUILD-SNAPSHOT.jar:2.1.0.BUILD-SNAPSHOT]
        at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:398) [spring-boot-2.1.0.BUILD-SNAPSHOT.jar:2.1.0.BUILD-SNAPSHOT]
        at org.springframework.boot.SpringApplication.run(SpringApplication.java:330) [spring-boot-2.1.0.BUILD-SNAPSHOT.jar:2.1.0.BUILD-SNAPSHOT]
        at org.springframework.boot.SpringApplication.run(SpringApplication.java:1234) [spring-boot-2.1.0.BUILD-SNAPSHOT.jar:2.1.0.BUILD-SNAPSHOT]
        at org.springframework.boot.SpringApplication.run(SpringApplication.java:1222) [spring-boot-2.1.0.BUILD-SNAPSHOT.jar:2.1.0.BUILD-SNAPSHOT]
        at com.example.test.Application.main(Application.java:11) [classes/:na]
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_171]
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_171]
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_171]
        at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_171]
        at org.springframework.boot.devtools.restart.RestartLauncher.run(RestartLauncher.java:49) [spring-boot-devtools-2.1.0.BUILD-SNAPSHOT.jar:2.1.0.BUILD-SNAPSHOT]

        2018-06-24 18:12:14.749 ERROR 72491 --- [  restartedMain] o.s.b.d.LoggingFailureAnalysisReporter   :

        ***************************
        APPLICATION FAILED TO START
        ***************************

        Description:

        Field userDAO in com.example.test.service.impl.UserServiceImpl required a bean of type 'com.example.test.dao.UserDAO' that could not be found.


        Action:

        Consider defining a bean of type 'com.example.test.dao.UserDAO' in your configuration.

我不確定為什么，但是在提到的位置有一個UserDAO類，並且無法識別。 我是否錯過任何注釋或其他內容？

Answer 1

找不到UserDAO實現。

您想擴展您的通用DAO實現：

@Repository
public class UserDAOImpl extends GenericRepositoryImplementation< UsersEntity> implements UserDAO {
     public UserDaoImpl() {
          super(UsersEntity.class);
     }
}

你的泛型DAO實現應該能夠接受一個類類型的<T>的，而不是一個實例T ：

public class GenericRepositoryImplementation<T> implements GenericRepositoryInterface<T> {

    protected EntityManager entityManager;
    private Class<T> type;

    public GenericRepositoryImplementation(Class<T> type) {
        // TODO Auto-generated constructor stub
        this.type = type;
    }
}

Answer 2

我認為問題出在您的UserDAOImpl。 在這里，您嘗試注入抽象類的依賴關系。 為userDao提供具體的類，然后將其注入到您的控制器/服務中。