PO即 Persistence Object
　　VO即 Value Object

　VO和PO的主要區別在于：
　　VO是獨立的Java Object。
　　PO是由Hibernate納入其實體容器（Entity Map）的對象，它代表了與數據庫中某條記錄對應的Hibernate實體，PO的變化在事務提交時將反應到實際數據庫中。

　實際上，這個VO被用作Data Transfer Object，即所謂的DTO。想必，VO就是Data Access Object ---DAO了啦。為什么要有這二者之分呢？如在傳統的MVC架構中，位于Model層的PO，是否允許被傳遞到其他層面。由于PO的更新最終將被映射到實際數據庫中，如果PO在其他層面（如View層）發生了變動，那么可能會對Model層造成意想不到的破壞。

　主要想說的還是如何進行二者之間的轉換：
　　屬性復制可以通過Apache Jakarta Commons Beanutils（http://jakarta.apache.org/commons/beanutils/）組件提供的屬性批量復制功能，避免繁復的get/set操作。down下來之后，里面的API DOC一應俱全。

　對于一些無需處理其它處理（如過濾）直接用BeanUtilsBean.copyProperties方法，其參考如下：

public static void copyProperties(java.lang.Object dest,
????????????????????????????????? java.lang.Object orig)
?????????????????????????? throws java.lang.IllegalAccessException,
????????????????????????????????? java.lang.reflect.InvocationTargetExceptioCopy property values from the origin bean to the destination bean for all cases where the property names are the same.
　范例１：

?TUser user? =?? new? TUser();
TUser anotherUser? =?? new? TUser();
user.setName( " Emma " );
user.setUserType( 1 );
?try??? {
BeanUtils.copyProperties(anotherUser,user);
System.out.println( " UserName =>? "
?+ anotherUser.getName()
);
System.out.println( " UserType =>? "
?+? anotherUser.getUserType()
);
}?? catch? (IllegalAccessException e)?? {
e.printStackTrace();
}?? catch? (InvocationTargetException e)?? {
e.printStackTrace();
} 　
?

　也可以利用其中的一些方法在copy屬性的時候達到自己的要求，如：

　范例２

? /** */ /** //*
?* Created on 2006-4-26
? */
?package? com.util;

?import? java.beans.PropertyDescriptor;
?import? java.util.Collection;

?import? org.apache.commons.beanutils.PropertyUtils;

?/** */ /**?? */ /** */ /**
?* CopyUtil
?*? @author? Jkallen
? */
? public?? class? CopyUtil?? {
???
???? /** */ /**?? */ /** */ /**
???? * Copy properties of orig to dest
???? * Exception the Entity and Collection Type
???? *? @param? dest
???? *? @param? orig
???? *? @return? the dest bean
????? */
????? public?? static? Object copyProperties(Object dest, Object orig)?? {
???????? if? (dest? ==?? null?? ||? orig? ==?? null )?? {
???????????? return? dest;
??????? }
???????
??????? PropertyDescriptor[] destDesc? =? PropertyUtils.getPropertyDescriptors(dest);
???????? try??? {
???????????? for? ( int? i? =?? 0 ; i? <? destDesc.length; i ++ )?? {
??????????????? Class destType? =? destDesc[i].getPropertyType();
??????????????? Class origType? =? PropertyUtils.getPropertyType(orig, destDesc[i].getName());
???????????????? if (destType? !=?? null?? &&? destType.equals(origType)
???????????????????????? &&?? ! destType.equals(Class. class ))?? {
???????????????????? if ( ! Collection. class .isAssignableFrom(origType))? {???????????????????
???????????????????????? try? {
??????????????????????????? Object value? =? PropertyUtils.getProperty(orig, destDesc[i].getName());
??????????????????????????? PropertyUtils.setProperty(dest, destDesc[i].getName(), value);
??????????????????????? } catch (Exception ex)? {???????????????????????????
??????????????????????? }
??????????????????? }
??????????????? }
??????????? }
???????????
???????????? return? dest;
??????? } catch (Exception ex)?? {
???????????? throw?? new? CopyException(ex);
?//???????????? return dest;
???????? }
??? }????
???
???? /** */ /**?? */ /** */ /**
???? * Copy properties of orig to dest
???? * Exception the Entity and Collection Type
???? *? @param? dest
???? *? @param? orig
???? *? @param? ignores
???? *? @return? the dest bean
????? */
????? public?? static? Object copyProperties(Object dest, Object orig, String[] ignores)?? {
???????? if? (dest? ==?? null?? ||? orig? ==?? null )?? {
???????????? return? dest;
??????? }
???????
??????? PropertyDescriptor[] destDesc? =? PropertyUtils.getPropertyDescriptors(dest);
???????? try??? {
???????????? for? ( int? i? =?? 0 ; i? <? destDesc.length; i ++ )?? {
???????????????? if? (contains(ignores, destDesc[i].getName()))?? {
???????????????????? continue ;
??????????????? }
???????????????
??????????????? Class destType? =? destDesc[i].getPropertyType();
??????????????? Class origType? =? PropertyUtils.getPropertyType(orig, destDesc[i].getName());
???????????????? if (destType? !=?? null?? &&? destType.equals(origType)
???????????????????????? &&?? ! destType.equals(Class. class ))?? {
???????????????????? if ( ! Collection. class .isAssignableFrom(origType))? {
??????????????????????? Object value? =? PropertyUtils.getProperty(orig, destDesc[i].getName());
??????????????????????? PropertyUtils.setProperty(dest, destDesc[i].getName(), value);
??????????????????? }
??????????????? }
??????????? }
???????????
???????????? return? dest;
??????? } catch (Exception ex)?? {
???????????? throw?? new? CopyException(ex);
??????? }
??? }
???
???? static?? boolean? contains(String[] ignores, String name)?? {
???????? boolean? ignored? =?? false ;
???????? for? ( int? j? =?? 0 ; ignores? !=?? null?? &&? j? <? ignores.length; j ++ )?? {
???????????? if? (ignores[j].equals(name))?? {
??????????????? ignored? =?? true ;
???????????????? break ;
??????????? }
??????? }
???????
???????? return? ignored;
??? }
}
?
?
　　

　　可以看到，在范例１中通過方法copyProperties的時候，二者之間在的屬性名必須相同（Copy property values from the origin bean to the destination bean for all cases where the property names are the same）。而在范例２中通過
?　　Object value = PropertyUtils.getProperty(orig, destDesc[i].getName());
? 　　PropertyUtils.setProperty(dest, destDesc[i].getName(), value);
　　也是將源與目的之間copy相同的屬性名。而VO是在前臺顯示，所以難免會用到PO中所不存在的屬性值。比如PO中可能是一個對象，而VO中則可能是此對象的全部屬性。其中的一些轉換則需要依據前臺需要針對性地處理啦！

Reference:? Apache DOC and <>