java - 为什么复合ID类必须实现Serializable？

Question

如果我创建了一个没有实现 Serializable 的复合 ID 类，例如:

@Entity
@Table(name = "board")
public class Board {
    @Id
    @Column(name = "keyword_news_id")
    private int id;

    @Id
    @Column(name = "board_no")
    private int boardNo;
....

错误发生如下:

Caused by: org.hibernate.MappingException: composite-id class must implement Serializable: com.estinternet.news.domain.IssueNewsBoard
    at org.hibernate.mapping.RootClass.checkCompositeIdentifier(RootClass.java:263)
    at org.hibernate.mapping.RootClass.validate(RootClass.java:244)
    at org.hibernate.cfg.Configuration.validate(Configuration.java:1362)
    at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1865)
    at org.springframework.orm.hibernate3.LocalSessionFactoryBean.newSessionFactory(LocalSessionFactoryBean.java:860)
    at org.springframework.orm.hibernate3.LocalSessionFactoryBean.buildSessionFactory(LocalSessionFactoryBean.java:779)
    at org.springframework.orm.hibernate3.AbstractSessionFactoryBean.afterPropertiesSet(AbstractSessionFactoryBean.java:211)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeInitMethods(AbstractAutowireCapableBeanFactory.java:1477)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1417)

Hibernate entity classes doesn't need to be Serializable .那么，为什么composite-id 类必须实现Serializable 呢？我读了this thread ，但它没有给我足够的信息。

Answer 1

session 对象需要可序列化，因此它引用的所有对象也必须是可序列化的。id 用作索引 session 中加载的对象的键。在 CompositeId 的情况下，类本身被用作 id。