使用 Spring、JPA 和 Hibernate 的通用 DAO 设置答案

【问题标题】：Generic DAO Setup using Spring, JPA and Hibernate使用 Spring、JPA 和 Hibernate 的通用 DAO 设置
【发布时间】：2018-06-24 20:54:33
【问题描述】：

我正在尝试制作一个通用代码，以在任何实体上实现一些最常见的操作。我使用 Spring Initializr 使用 Gradle、Spring Boot 2.1.0 SNAPSHOT、JPA 和 Hibernate 生成产品的基础。我使用 MySQL Workbench 创建了模式和表，并使用它为我的项目生成实体。所以谈到实际问题，我尝试创建一个通用 DAO，其中一些常见的操作，如 findbyid、编辑、删除、创建、更新、getall 将被实现，然后将其扩展到其他 DAO 类以提高可重用性并完成工作快点。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);
    }
}

我不确定我的实现哪里出了问题，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.

我不知道为什么，但在提到的位置有一个 UserDAO 类，它无法识别它。我是否遗漏了任何注释或任何内容？

【问题讨论】：

标签： java spring hibernate

【解决方案1】：

找不到UserDAO 的实现。

您想要扩展您的通用 DAO 实现：

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

您的通用 DAO 实现应该接受 <T> 类型的类，而不是 T 的实例：

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;
    }
}

【讨论】：

谢谢！我完全忽略了我使用抽象类并且扩展没有正确完成的问题。

【解决方案2】：

我认为问题在于您的 UserDAOImpl。在这里，您尝试注入抽象类的依赖项。为 userDao 提供具体类，然后将其注入您的控制器/服务。

【讨论】：