各位高手，我在使用hibernate、jpa、springdata集成時遇到了如下的問題：1.model@Entity@Table(name="group",schema="sc")@Inheritance(strategy =  InheritanceType.TABLE_PER_CLASS)public class Group extends AbstractEntity{    ...        @ElementCollection(fetch= FetchType.EAGER)    @NotNull    @Column(name="user")    @CollectionTable(name = "t_group_users", schema = "sc", joinColumns = @JoinColumn(name = "group_id"))    private List<String> users;}2.repositorypublic interface GroupRepository extends CrudRepository<Group, UUID>{}3.config@Configuration@EnableJpaRepositories(basePackages = { "com.**.**" })public class RepositoryTestConfig{    @Bean    public PlatformTransactionManager transactionManager(EntityManagerFactory emf)    {        JpaTransactionManager transactionManager = new JpaTransactionManager();        transactionManager.setEntityManagerFactory(emf);        return transactionManager;    }    @Bean    public LocalContainerEntityManagerFactoryBean entityManagerFactory(DataSource dataSource)    {        LocalContainerEntityManagerFactoryBean emfb = new LocalContainerEntityManagerFactoryBean();        emfb.setDataSource(dataSource());        emfb.setJpaVendorAdapter(jpaVendorAdapter());        emfb.setPackagesToScan("com.**.**.model");        Properties properties = new Properties();        properties.setProperty("hibernate.hbm2ddl.auto", "create");        properties.setProperty("hibernate.format_sql", "true");        emfb.setJpaProperties(properties);        return emfb;    }    @Bean    public JpaVendorAdapter jpaVendorAdapter()    {        HibernateJpaVendorAdapter adapter = new HibernateJpaVendorAdapter();        adapter.setDatabase(Database.H2);        adapter.setShowSql(false);        adapter.setGenerateDdl(false);        adapter.setDatabasePlatform("org.hibernate.dialect.H2Dialect");        return adapter;    } 但我使用groupRepository.findOne方法時，users返回的是org.hibernate.collection.internal.PersistentBag類型，而不是ArrayList類型，請問是什么原因？