使用Spring，JPA和Hibernate的通用DAO设置

Question

我正在尝试编写一个通用代码，以在任何实体上实现一些最常见的操作。 我已经使用Spring Initializr使用Gradle，Spring Boot 2.1.0 SNAPSHOT，JPA和Hibernate来生成产品的基础。 我使用MySQL Workbench创建了架构和表，并使用它们为我的项目生成了实体。 因此，针对实际问题，我尝试创建一个通用的DAO，在其中将实现一些常见的操作（例如findbyid，edit，delete，create，update，getall），然后将其扩展到其他DAO类以促进可重用性并进行工作。快点。 所以这是我到目前为止的代码：

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);
    }
}

我不确定实现的地方在哪里，但是每当我运行应用程序时，它都会崩溃并显示以下日志：

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.

我不确定为什么，但是在提到的位置有一个UserDAO类，并且无法识别。 我是否错过任何注释或其他内容？

Answer 1

找不到UserDAO实现。

您想扩展您的通用DAO实现：

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

你的泛型DAO实现应该能够接受一个类类型的<T>的，而不是一个实例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

我认为问题出在您的UserDAOImpl。 在这里，您尝试注入抽象类的依赖关系。 为userDao提供具体的类，然后将其注入到您的控制器/服务中。