我是否需要Persistence.xml中的<class>元素？我有一個非常簡單的sistance.xml文件：<?xml version="1.0" encoding="UTF-8"?><persistence version="1.0"     xmlns="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"     xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_1_0.xsd">     <persistence-unit name="eventractor" transaction-type="RESOURCE_LOCAL">         <class>pl.michalmech.eventractor.domain.User</class>         <class>pl.michalmech.eventractor.domain.Address</class>         <class>pl.michalmech.eventractor.domain.City</class>         <class>pl.michalmech.eventractor.domain.Country</class>         <properties>             <property name="hibernate.hbm2ddl.auto" value="validate" />             <property name="hibernate.show_sql" value="true" />         </properties>     </persistence-unit></persistence>而且起作用了。但當我移除<class>元素應用程序看不到實體(所有類都用@Entity).有沒有自動掃描機制@Entity上課？