Question

在我目前的Spring项目中，我在rootCOntext.xml文件上有这个Hibernate配置：

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xmlns:p="http://www.springframework.org/schema/p"
        xmlns:context="http://www.springframework.org/schema/context"
        xmlns:security="http://www.springframework.org/schema/security"
        xmlns:mvc="http://www.springframework.org/schema/mvc"
        xmlns:tx="http://www.springframework.org/schema/tx"
        xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd http://www.springframework.org/schema/security http://www.springframework.org/schema/security/spring-security.xsd http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc.xsd http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx.xsd">  

    <bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close">
        <property name="driverClassName" value="org.postgresql.Driver"/>
        <property name="url" value="jdbc:postgresql:mydata"/>
        <property name="username" value="klebermo"/>
        <property name="password" value="123"/>
    </bean>

    <bean id="hibernate4AnnotatedSessionFactory" class="org.springframework.orm.hibernate4.LocalSessionFactoryBean">
        <property name="dataSource" ref="dataSource"/>
        <property name="packagesToScan" value="org.kleber.model" />
        <property name="hibernateProperties">
            <props>
                <prop key="hibernate.dialect">org.hibernate.dialect.PostgreSQLDialect</prop>
                <prop key="hibernate.show_sql">false</prop>
                <prop key="hibernate.hbm2ddl.auto">create-drop</prop>
            </props>
        </property>
    </bean>

    <bean id="transactionManager" class="org.springframework.orm.hibernate4.HibernateTransactionManager">
        <property name="sessionFactory" ref="hibernate4AnnotatedSessionFactory"/>
    </bean>

    <tx:annotation-driven transaction-manager="transactionManager"/>
</beans>

但是当应用程序需要执行此查询时：

@Transactional
public List<E> select(String orderby, String groupby) {
    return (List<E>) this.getCurrentSession().createCriteria(clazz).setResultTransformer(Criteria.DISTINCT_ROOT_ENTITY).list();
}

包含在此类中：

public abstract class Dao<E> {
    protected Class<E> clazz;

    @Autowired
    protected SessionFactory sessionFactory;

    public Dao(Class<E> clazz) {
        this.clazz = clazz;
    }

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

我收到此错误：

org.hibernate.HibernateException: Could not obtain transaction-synchronized Session for current thread
    org.springframework.orm.hibernate4.SpringSessionContext.currentSession(SpringSessionContext.java:134)
    org.hibernate.internal.SessionFactoryImpl.getCurrentSession(SessionFactoryImpl.java:456)
    org.kleber.model.Dao.getCurrentSession(Dao.java:22)
    org.kleber.model.Dao.select(Dao.java:43)
    org.kleber.model.Service.select(Service.java:35)
    org.kleber.model.Controller.list(Controller.java:87)
    org.kleber.model.Controller$$FastClassBySpringCGLIB$$aa38cb3a.invoke(<generated>)
    org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:204)
    org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:652)
    org.kleber.model.usuario.UsuarioController$$EnhancerBySpringCGLIB$$7dce8c33.list(<generated>)
    sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    java.lang.reflect.Method.invoke(Method.java:498)
    org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:205)
    org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:133)
    org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:116)
    org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:827)
    org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:738)
    org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85)
    org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:963)
    org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:897)
    org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970)
    org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:861)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:622)
    org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:317)
    org.springframework.security.web.access.intercept.FilterSecurityInterceptor.invoke(FilterSecurityInterceptor.java:127)
    org.springframework.security.web.access.intercept.FilterSecurityInterceptor.doFilter(FilterSecurityInterceptor.java:91)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
    org.springframework.security.web.access.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:114)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
    org.springframework.security.web.session.SessionManagementFilter.doFilter(SessionManagementFilter.java:137)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
    org.springframework.security.web.authentication.AnonymousAuthenticationFilter.doFilter(AnonymousAuthenticationFilter.java:111)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
    org.springframework.security.web.authentication.rememberme.RememberMeAuthenticationFilter.doFilter(RememberMeAuthenticationFilter.java:158)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
    org.springframework.security.web.servletapi.SecurityContextHolderAwareRequestFilter.doFilter(SecurityContextHolderAwareRequestFilter.java:170)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
    org.springframework.security.web.savedrequest.RequestCacheAwareFilter.doFilter(RequestCacheAwareFilter.java:63)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
    org.springframework.security.web.authentication.www.BasicAuthenticationFilter.doFilterInternal(BasicAuthenticationFilter.java:158)
    org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
    org.springframework.security.web.authentication.AbstractAuthenticationProcessingFilter.doFilter(AbstractAuthenticationProcessingFilter.java:200)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
    org.springframework.security.web.authentication.logout.LogoutFilter.doFilter(LogoutFilter.java:116)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
    org.springframework.security.web.header.HeaderWriterFilter.doFilterInternal(HeaderWriterFilter.java:64)
    org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
    org.springframework.security.web.context.request.async.WebAsyncManagerIntegrationFilter.doFilterInternal(WebAsyncManagerIntegrationFilter.java:56)
    org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
    org.springframework.security.web.context.SecurityContextPersistenceFilter.doFilter(SecurityContextPersistenceFilter.java:105)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
    org.springframework.security.web.FilterChainProxy.doFilterInternal(FilterChainProxy.java:214)
    org.springframework.security.web.FilterChainProxy.doFilter(FilterChainProxy.java:177)
    org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:346)
    org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:262)

任何人都可以看到这里有什么问题？

更新

我改变了我的DAO方法：

@Transactional
public List<E> select(String orderby, String groupby) {
    Session sess = sessionFactory.openSession();
    Transaction tx = null;
    List<E> list = null;
    try {
        tx = sess.beginTransaction();
        list = sess.createCriteria(clazz).setResultTransformer(Criteria.DISTINCT_ROOT_ENTITY).list();
        tx.commit();
    } catch (Exception e) {
        if(tx != null)
            tx.rollback();
        throw e;
    } finally {
        sess.close();
    }
    return list;
    //return (List<E>) this.getCurrentSession().createCriteria(clazz).setResultTransformer(Criteria.DISTINCT_ROOT_ENTITY).list();
}

现在我收到了这个错误：

org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: org.kleber.model.usuario.Usuario.listas, could not initialize proxy - no Session
    org.hibernate.collection.internal.AbstractPersistentCollection.throwLazyInitializationException(AbstractPersistentCollection.java:582)
    org.hibernate.collection.internal.AbstractPersistentCollection.withTemporarySessionIfNeeded(AbstractPersistentCollection.java:201)
    org.hibernate.collection.internal.AbstractPersistentCollection.readSize(AbstractPersistentCollection.java:145)
    org.hibernate.collection.internal.PersistentBag.size(PersistentBag.java:261)
    com.fasterxml.jackson.databind.ser.std.CollectionSerializer.serialize(CollectionSerializer.java:102)
    com.fasterxml.jackson.databind.ser.std.CollectionSerializer.serialize(CollectionSerializer.java:25)
    com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:704)
    com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:690)
    com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:155)
    com.fasterxml.jackson.databind.ser.impl.IndexedListSerializer.serializeContents(IndexedListSerializer.java:119)
    com.fasterxml.jackson.databind.ser.impl.IndexedListSerializer.serialize(IndexedListSerializer.java:79)
    com.fasterxml.jackson.databind.ser.impl.IndexedListSerializer.serialize(IndexedListSerializer.java:18)
    com.fasterxml.jackson.databind.ser.DefaultSerializerProvider.serializeValue(DefaultSerializerProvider.java:292)
    com.fasterxml.jackson.databind.ObjectMapper._configAndWriteValue(ObjectMapper.java:3681)
    com.fasterxml.jackson.databind.ObjectMapper.writeValueAsString(ObjectMapper.java:3057)
    org.kleber.model.Controller.list(Controller.java:88)
    org.kleber.model.Controller$$FastClassBySpringCGLIB$$aa38cb3a.invoke(<generated>)
    org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:204)
    org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:652)
    org.kleber.model.usuario.UsuarioController$$EnhancerBySpringCGLIB$$7c57ca50.list(<generated>)
    sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    java.lang.reflect.Method.invoke(Method.java:498)
    org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:205)
    org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:133)
    org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:116)
    org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:827)
    org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:738)
    org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85)
    org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:963)
    org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:897)
    org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970)
    org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:861)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:622)
    org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:317)
    org.springframework.security.web.access.intercept.FilterSecurityInterceptor.invoke(FilterSecurityInterceptor.java:127)
    org.springframework.security.web.access.intercept.FilterSecurityInterceptor.doFilter(FilterSecurityInterceptor.java:91)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
    org.springframework.security.web.access.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:114)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
    org.springframework.security.web.session.SessionManagementFilter.doFilter(SessionManagementFilter.java:137)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
    org.springframework.security.web.authentication.AnonymousAuthenticationFilter.doFilter(AnonymousAuthenticationFilter.java:111)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
    org.springframework.security.web.authentication.rememberme.RememberMeAuthenticationFilter.doFilter(RememberMeAuthenticationFilter.java:158)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
    org.springframework.security.web.servletapi.SecurityContextHolderAwareRequestFilter.doFilter(SecurityContextHolderAwareRequestFilter.java:170)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
    org.springframework.security.web.savedrequest.RequestCacheAwareFilter.doFilter(RequestCacheAwareFilter.java:63)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
    org.springframework.security.web.authentication.www.BasicAuthenticationFilter.doFilterInternal(BasicAuthenticationFilter.java:158)
    org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
    org.springframework.security.web.authentication.AbstractAuthenticationProcessingFilter.doFilter(AbstractAuthenticationProcessingFilter.java:200)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
    org.springframework.security.web.authentication.logout.LogoutFilter.doFilter(LogoutFilter.java:116)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
    org.springframework.security.web.header.HeaderWriterFilter.doFilterInternal(HeaderWriterFilter.java:64)
    org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
    org.springframework.security.web.context.request.async.WebAsyncManagerIntegrationFilter.doFilterInternal(WebAsyncManagerIntegrationFilter.java:56)
    org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
    org.springframework.security.web.context.SecurityContextPersistenceFilter.doFilter(SecurityContextPersistenceFilter.java:105)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
    org.springframework.security.web.FilterChainProxy.doFilterInternal(FilterChainProxy.java:214)
    org.springframework.security.web.FilterChainProxy.doFilter(FilterChainProxy.java:177)
    org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:346)
    org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:262)

我想我指的是如何在Model层中实现我的类之间的关系。

这是我的班级：

public class Usuario {
@Id
@GeneratedValue(strategy=GenerationType.IDENTITY)
private Integer id;

@Column
@Input
@Text
private String login;

@Column
@Input
@Password
private String senha;

@Column
@Input
@Text
private String nome;

@Column
@Input
@Text
private String sobrenome;

@Column
@Input
@Email
private String email;

@OneToOne
private Cart cesta;

@ManyToMany
private List<Wishlist> listas;

@ManyToMany
private List<Orders> pedidos;

@ManyToMany
@Select
private List<Credencial> credenciais;

@Column
@Input
@Date
private java.util.Date expirationDate;

@Column
@Input
@Checkbox
private Boolean locked;

@Column
@Input
@Checkbox
private Boolean enabled;
}

有人知道如何解决这个问题？不使用FetchType.EAGER ManyToMany关系（如果我这样做，应用程序甚至无法启动，因为我收到错误，hibernate无法获取多个包）。

更新2

我在我的DAO方法中尝试这个：

@Transactional
public List<E> select(String orderby, String groupby) {
    Session sess = sessionFactory.openSession();
    Transaction tx = null;
    List<E> list = null;
    try {
        tx = sess.beginTransaction();

        Criteria criteria = this.getCurrentSession().createCriteria(clazz);
        if(orderby != null)
            criteria = criteria.addOrder( Order.asc(orderby) );
        if(groupby != null)
            //TODO
        for(Field field : clazz.getDeclaredFields()) {
            if(field.isAnnotationPresent(ManyToMany.class))
                criteria = criteria.setFetchMode(field.getName(), FetchMode.EAGER);
        }
        list = criteria.list();

        tx.commit();
    } catch (Exception e) {
        if(tx != null)
            tx.rollback();
        throw e;
    } finally {
        sess.close();
    }
    return list;
}

现在我收到了这篇文章中提到的第一个错误。

更新3

因此，我设法修复此错误，将方法getCurrentSession() Dao类更改为：

public Session getCurrentSession() {
    return sessionFactory.openSession();
}

但是现在当我从表单提交数据时，尽管没有触发错误，但它们不会保留在数据库中。

Answer 1

我使用与您相同的包，我在xml配置文件中有这两个附加条目：

<context:component-scan base-package="com.mypkg.daos"/>
<context:annotation-config/>

当您使用@Transactional和@Autowried注释时，我想添加这两个配置属性是个好主意。

Answer 2

我想春天无法正确注入SessionFactory

我会在你的XML中启用spring注释事务;试着看看http://docs.spring.io/spring/docs/current/spring-framework-reference/html/transaction.html;您应该启用事务，或者在配置类中添加@EnableTransactionManagement或在XML中添加：<tx:annotation-driven/>

然后我要做的是：

我写这个存储库DAO

   @Repository
     public class Dao<E> {
        protected Class<E> clazz;

        @Autowired
        protected SessionFactory sessionFactory;

        public Dao(Class<E> clazz) {
            this.clazz = clazz;
        }

        public Session getCurrentSession() {
            return sessionFactory.getCurrentSession();
        }
        public List<E> select(String orderby, String groupby) 
        {
         return (List<E>) this.getCurrentSession().createCriteria(clazz).setResultTransformer(Criteria.DISTINCT_ROOT_ENTITY).list();
        }
    }

然后我创建一个服务类，我将执行以下操作

@Service
public class ServiceClass<E>
{
  @Autowired
  private Dao<E> repos;

@Transactional
public List<E> select(String orderby, String groupby) {
    return repos.select(orderby, groupby);
}
}

我希望这是有用的

安吉洛

Answer 3

我建议您尝试在 transactionManager 而不是 sessionFactory 上设置数据源，如下所示：

<bean id="transactionManager" class="org.springframework.orm.hibernate4.HibernateTransactionManager">
    <property name="dataSource" ref="dataSource"/>
</bean>

此更改的原因可在此link上找到。另外，请确保您拥有以下内容：

<tx:annotation-driven transaction-manager="transactionManager"/>在xml文件中声明，rootContext.xml.
<context:component-scan base-package="com.myproject"/>让bean可以看到Spring。
@Repository。
@Transactional关于您的方法或班级。
1. 和4.让Spring通过Transaction支持应用和创建代理。

Answer 4

您的代码存在多个问题。让我们从头开始。

@Transactional无效。从您复制的堆栈跟踪中可以清楚地看到这一点，因为Spring使用代理对象来实现事务性调用。我看，你的配置应该没问题，所以我唯一能想到的就是你使用了错误的注释。

不幸的是，有2个@Transactional注释，一个来自javax.transaction包，另一个来自org.springframework.transaction.annotation包。显然，你必须使用后者，否则它将无法正常工作。

第二件事，懒惰初始化异常。发生这种情况是因为您尝试在事务之外初始化惰性关系。

有多种解决方案：

在交易中获取
使用原始查询直接获取

第一件事将解决问题，但与第二个解决方案相比，它不会表现得非常好。

首先，您可以通过调用延迟集合上的任何方法来执行此操作，例如

list.getLazyCollection().size()

或者您可以使用Hibernate的机制来执行此操作：

Hibernate.initialize(list.getLazyCollection())

唯一重要的是在交易中执行此操作。

后一个解决方案直接获取关系涉及JPQL / HQL查询或您的案例中的Criteria API。

Hibernate不会在数据库上保留数据（参见更新3）

4 个答案: