Facade用的非常的廣了，以前剛接觸的時候有個誤解，總覺得Facade是簡單的，而它后面的支撐服務是復雜的，對于客戶來說卻是簡單的，現在來看，不完全對，或者說只是說對了一半，因為有時候恰恰是Facade是復雜的.
我們舉一個例子，比如發送短信，我們一般就定義一個MessageService的服務類，里面只提供一個方法就行了，sendToUser(String phone,String content)
但是到了客戶端的時候有了自己的 "方言",比如它不是關心一個抽象的用戶，它只知道向教師發送短信，或者向學生發送短信，或者向家長發送短信。
示例如下:
由圖中可以看到，Facade的內容非常豐富，而支撐它的服務類卻很簡單，在開發過程中我們一般先實現通用的ServiceA,然后根據進一步的需求做一個面向具體復雜的Facade.
在Spring提供的sample里發現一個小技巧，就是Facade和ServiceA都是接口，然后提供一個實現二者的支撐類:
public?class?PetStoreAnnotationImpl?implements?PetStoreFacade,?OrderService?{
????private?AccountDao?accountDao;
????private?CategoryDao?categoryDao;
????private?ProductDao?productDao;
????private?ItemDao?itemDao;
????private?OrderDao?orderDao;
????//-------------------------------------------------------------------------
????//?Setter?methods?for?dependency?injection
????//-------------------------------------------------------------------------
????public?void?setAccountDao(AccountDao?accountDao)?{
????????this.accountDao?=?accountDao;
????}
????public?void?setCategoryDao(CategoryDao?categoryDao)?{
????????this.categoryDao?=?categoryDao;
????}
????public?void?setProductDao(ProductDao?productDao)?{
????????this.productDao?=?productDao;
????}
????public?void?setItemDao(ItemDao?itemDao)?{
????????this.itemDao?=?itemDao;
????}
????public?void?setOrderDao(OrderDao?orderDao)?{
????????this.orderDao?=?orderDao;
????}
????//-------------------------------------------------------------------------
????//?Operation?methods,?implementing?the?PetStoreFacade?interface
????//-------------------------------------------------------------------------
????public?Account?getAccount(String?username)?{
????????return?this.accountDao.getAccount(username);
????}
????public?Account?getAccount(String?username,?String?password)?{
????????return?this.accountDao.getAccount(username,?password);
????}
????public?void?insertAccount(Account?account)?{
????????this.accountDao.insertAccount(account);
????}
????public?void?updateAccount(Account?account)?{
????????this.accountDao.updateAccount(account);
????}
????public?List?getUsernameList()?{
????????return?this.accountDao.getUsernameList();
????}
????public?List?getCategoryList()?{
????????return?this.categoryDao.getCategoryList();
????}
????public?Category?getCategory(String?categoryId)?{
????????return?this.categoryDao.getCategory(categoryId);
????}
????public?List?getProductListByCategory(String?categoryId)?{
????????return?this.productDao.getProductListByCategory(categoryId);
????}
????public?List?searchProductList(String?keywords)?{
????????return?this.productDao.searchProductList(keywords);
????}
????public?Product?getProduct(String?productId)?{
????????return?this.productDao.getProduct(productId);
????}
????public?List?getItemListByProduct(String?productId)?{
????????return?this.itemDao.getItemListByProduct(productId);
????}
????public?Item?getItem(String?itemId)?{
????????return?this.itemDao.getItem(itemId);
????}
????public?boolean?isItemInStock(String?itemId)?{
????????return?this.itemDao.isItemInStock(itemId);
????}
????public?void?insertOrder(Order?order)?{
????????this.orderDao.insertOrder(order);
????????this.itemDao.updateQuantity(order);
????}
????public?Order?getOrder(int?orderId)?{
????????return?this.orderDao.getOrder(orderId);
????}
????public?List?getOrdersByUsername(String?username)?{
????????return?this.orderDao.getOrdersByUsername(username);
????}
}
看起來似乎不錯，不過仔細想想個人認為還是不是太好,總的感覺就是層次不清晰，因為很多時候Facade和Service之間是被服務與服務的關系，所以理當分開。 同時，這個類有點傾向于"萬能類"了，能分還是分開好.這和我們以前提到的dao又背離過來了（以前我們提倡一個業務一個dao,現在覺得只用一個通用的dao更合適）,這個并不矛盾，具體問題具體看待.
歡迎各位拍磚.