【引用】http://www.javaeye.com/topic/11712
在最近的圍繞domain object的討論中浮現(xiàn)出來(lái)了三種模型，(還有一些其他的旁枝，不一一分析了)，經(jīng)過一番討論，各種問題逐漸清晰起來(lái)，在這里我試圖做一個(gè)總結(jié)，便于大家了解和掌握。
第一種模型：只有g(shù)etter/setter方法的純數(shù)據(jù)類，所有的業(yè)務(wù)邏輯完全由business object來(lái)完成(又稱TransactionScript)，這種模型下的domain object被Martin Fowler稱之為“貧血的domain object”。下面用舉一個(gè)具體的代碼來(lái)說(shuō)明，代碼來(lái)自Hibernate的caveatemptor，但經(jīng)過我的改寫：
一個(gè)實(shí)體類叫做Item，指的是一個(gè)拍賣項(xiàng)目
一個(gè)DAO接口類叫做ItemDao
一個(gè)DAO接口實(shí)現(xiàn)類叫做ItemDaoHibernateImpl
一個(gè)業(yè)務(wù)邏輯類叫做ItemManager(或者叫做ItemService)
- public class Item implements Serializable {
- private Long id = null;
- private int version;
- private String name;
- private User seller;
- private String description;
- private MonetaryAmount initialPrice;
- private MonetaryAmount reservePrice;
- private Date startDate;
- private Date endDate;
- private Set categorizedItems = new HashSet();
- private Collection bids = new ArrayList();
- private Bid successfulBid;
- private ItemState state;
- private User approvedBy;
- private Date approvalDatetime;
- private Date created = new Date();
-
- }
public class Item implements Serializable {
private Long id = null;
private int version;
private String name;
private User seller;
private String description;
private MonetaryAmount initialPrice;
private MonetaryAmount reservePrice;
private Date startDate;
private Date endDate;
private Set categorizedItems = new HashSet();
private Collection bids = new ArrayList();
private Bid successfulBid;
private ItemState state;
private User approvedBy;
private Date approvalDatetime;
private Date created = new Date();
// getter/setter方法省略不寫，避免篇幅太長(zhǎng)
}
- public interface ItemDao {
- public Item getItemById(Long id);
- public Collection findAll();
- public void updateItem(Item item);
- }
public interface ItemDao {
public Item getItemById(Long id);
public Collection findAll();
public void updateItem(Item item);
}
ItemDao定義持久化操作的接口，用于隔離持久化代碼。
- public class ItemDaoHibernateImpl implements ItemDao extends HibernateDaoSupport {
- public Item getItemById(Long id) {
- return (Item) getHibernateTemplate().load(Item.class, id);
- }
- public Collection findAll() {
- return (List) getHibernateTemplate().find("from Item");
- }
- public void updateItem(Item item) {
- getHibernateTemplate().update(item);
- }
- }
public class ItemDaoHibernateImpl implements ItemDao extends HibernateDaoSupport {
public Item getItemById(Long id) {
return (Item) getHibernateTemplate().load(Item.class, id);
}
public Collection findAll() {
return (List) getHibernateTemplate().find("from Item");
}
public void updateItem(Item item) {
getHibernateTemplate().update(item);
}
}
ItemDaoHibernateImpl完成具體的持久化工作，請(qǐng)注意，數(shù)據(jù)庫(kù)資源的獲取和釋放是在ItemDaoHibernateImpl里面處理的，每個(gè)DAO方法調(diào)用之前打開Session，DAO方法調(diào)用之后，關(guān)閉Session。(Session放在ThreadLocal中，保證一次調(diào)用只打開關(guān)閉一次)
- public class ItemManager {
- private ItemDao itemDao;
- public void setItemDao(ItemDao itemDao) { this.itemDao = itemDao;}
- public Bid loadItemById(Long id) {
- itemDao.loadItemById(id);
- }
- public Collection listAllItems() {
- return itemDao.findAll();
- }
- public Bid placeBid(Item item, User bidder, MonetaryAmount bidAmount,
- Bid currentMaxBid, Bid currentMinBid) throws BusinessException {
- if (currentMaxBid != null && currentMaxBid.getAmount().compareTo(bidAmount) > 0) {
- throw new BusinessException("Bid too low.");
- }
-
-
- if ( !state.equals(ItemState.ACTIVE) )
- throw new BusinessException("Auction is not active yet.");
-
-
- if ( item.getEndDate().before( new Date() ) )
- throw new BusinessException("Can't place new bid, auction already ended.");
-
-
- Bid newBid = new Bid(bidAmount, item, bidder);
-
-
- item.getBids().add(newBid);
- itemDao.update(item);
- return newBid;
- }
- }
public class ItemManager {
private ItemDao itemDao;
public void setItemDao(ItemDao itemDao) { this.itemDao = itemDao;}
public Bid loadItemById(Long id) {
itemDao.loadItemById(id);
}
public Collection listAllItems() {
return itemDao.findAll();
}
public Bid placeBid(Item item, User bidder, MonetaryAmount bidAmount,
Bid currentMaxBid, Bid currentMinBid) throws BusinessException {
if (currentMaxBid != null && currentMaxBid.getAmount().compareTo(bidAmount) > 0) {
throw new BusinessException("Bid too low.");
}
// Auction is active
if ( !state.equals(ItemState.ACTIVE) )
throw new BusinessException("Auction is not active yet.");
// Auction still valid
if ( item.getEndDate().before( new Date() ) )
throw new BusinessException("Can't place new bid, auction already ended.");
// Create new Bid
Bid newBid = new Bid(bidAmount, item, bidder);
// Place bid for this Item
item.getBids().add(newBid);
itemDao.update(item); // 調(diào)用DAO完成持久化操作
return newBid;
}
}
事務(wù)的管理是在ItemManger這一層完成的，ItemManager實(shí)現(xiàn)具體的業(yè)務(wù)邏輯。除了常見的和CRUD有關(guān)的簡(jiǎn)單邏輯之外，這里還有一個(gè)placeBid的邏輯，即項(xiàng)目的競(jìng)標(biāo)。
以上是一個(gè)完整的第一種模型的示例代碼。在這個(gè)示例中，placeBid，loadItemById，findAll等等業(yè)務(wù)邏輯統(tǒng)統(tǒng)放在ItemManager中實(shí)現(xiàn)，而Item只有g(shù)etter/setter方法。