Question

我尝试将我的Dao类使用的常用方法集中在一个Generic类中，如下所示：

public class Dao<E> {

    private final E entity;

    @Autowired
    SessionFactory sessionFactory;

    protected Session getCurrentSession(){
        return sessionFactory.getCurrentSession();
    }

    public Dao(E entity) {  
        this.entity = entity;
    }

    public E getEntity() {
        return this.entity;
    }

    @Transactional
    public boolean persist(E transientInstance) {
        try {
            sessionFactory.getCurrentSession().persist(transientInstance);
            return true;
        } catch (RuntimeException re) {
            return false;
        }
    }

    @Transactional
    public boolean remove(E transientInstance) {
        try {
            sessionFactory.getCurrentSession().delete(transientInstance);
            return true;
        } catch (RuntimeException re) {
            return false;
        }
    }

    @SuppressWarnings("unchecked")
    @Transactional
    public E merge(E detachedInstance) {
        try {
            E result = (E) sessionFactory.getCurrentSession().merge(detachedInstance);
            return result;
        } catch (RuntimeException re) {
            return null;
        }
    }

    @SuppressWarnings("unchecked")
    @Transactional
    public E findById(int id) {
        try {
            E instance = (E) sessionFactory.getCurrentSession().get(entity.getClass(), id);
            return instance;
        } catch (RuntimeException re) {
            return null;
        }
    }

    @SuppressWarnings("unchecked")
    @Transactional
    public E findByUsername(String username) {
        try {
            E instance = (E) sessionFactory.getCurrentSession().createCriteria(entity.getClass(), username).add(Restrictions.like("login", username)).list().get(0);
            return instance;
        } catch (RuntimeException re) {
            return null;
        }
    }

    @SuppressWarnings("unchecked")
    @Transactional
    public List<E> findAll() {
        try {
            List<E> instance = sessionFactory.getCurrentSession().createCriteria(entity.getClass()).list();
            return instance;
        } catch (RuntimeException re) {
            return null;
        }
    }

}

我的Dao课是这样写的：

@Repository
public class UsuarioHome extends Dao<Usuario> {

    public UsuarioHome(Usuario entity) {
        super(entity);
        // TODO Auto-generated constructor stub
    }

}

但是当我尝试运行应用程序时出现此错误：

Caused by: org.springframework.beans.factory.BeanCreationException: Could not autowire field: private com.spring.webapp.lojavirtual.acesso.persistence.UsuarioHome com.spring.webapp.lojavirtual.acesso.service.AuthenticationService.accountDao; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'usuarioHome' defined in file [/home/kleber/workspace/.metadata/.plugins/org.eclipse.wst.server.core/tmp0/wtpwebapps/webapp2/WEB-INF/classes/com/spring/webapp/lojavirtual/acesso/persistence/UsuarioHome.class]: Instantiation of bean failed; nested exception is org.springframework.beans.BeanInstantiationException: Could not instantiate bean class [com.spring.webapp.lojavirtual.acesso.persistence.UsuarioHome]: No default constructor found; nested exception is java.lang.NoSuchMethodException: com.spring.webapp.lojavirtual.acesso.persistence.UsuarioHome.<init>()
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:514)
    at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:87)
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:285)
    ... 48 more
Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'usuarioHome' defined in file [/home/kleber/workspace/.metadata/.plugins/org.eclipse.wst.server.core/tmp0/wtpwebapps/webapp2/WEB-INF/classes/com/spring/webapp/lojavirtual/acesso/persistence/UsuarioHome.class]: Instantiation of bean failed; nested exception is org.springframework.beans.BeanInstantiationException: Could not instantiate bean class [com.spring.webapp.lojavirtual.acesso.persistence.UsuarioHome]: No default constructor found; nested exception is java.lang.NoSuchMethodException: com.spring.webapp.lojavirtual.acesso.persistence.UsuarioHome.<init>()
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateBean(AbstractAutowireCapableBeanFactory.java:1007)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:953)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:487)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:458)
    at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:295)
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:223)
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:292)
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:194)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.findAutowireCandidates(DefaultListableBeanFactory.java:912)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:855)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:770)
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:486)
    ... 50 more
Caused by: org.springframework.beans.BeanInstantiationException: Could not instantiate bean class [com.spring.webapp.lojavirtual.acesso.persistence.UsuarioHome]: No default constructor found; nested exception is java.lang.NoSuchMethodException: com.spring.webapp.lojavirtual.acesso.persistence.UsuarioHome.<init>()
    at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:83)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateBean(AbstractAutowireCapableBeanFactory.java:1000)
    ... 61 more
Caused by: java.lang.NoSuchMethodException: com.spring.webapp.lojavirtual.acesso.persistence.UsuarioHome.<init>()
    at java.lang.Class.getConstructor0(Class.java:2810)
    at java.lang.Class.getDeclaredConstructor(Class.java:2053)
    at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:78)
    ... 62 more

任何人都可以说我的方法是否真的有效，如果是真的，我在这里错过了什么？

Answer 1

您在UsuarioHome中缺少一个无参数构造函数。添加一个，spring应该能够实例化它。

@Repository
public class UsuarioHome extends Dao<Usuario> {

    public UsuarioHome() { //<---
        super(null);
    } 

    public UsuarioHome(Usuario entity) {
        super(entity);
        // TODO Auto-generated constructor stub
    }
}

我建议的一件事是没有字段 - private final E entity;。这真的没用。

此外，最好从DAO中取出交易设置并将其放入您的服务中。

使用泛型时Dao类中的错误

1 个答案: