Jpetstore阅读心得之分层结构

虽然对Spring不熟悉，又不懂iBatis，而且对模式的概念还没有弄清楚，但也硬着头皮去读Spring包自带的Jpetstore经典J2EE例子。

可以肯定，Jpetstore是按照MVC模式设计的。持久化层用iBatis（这个我不懂，我希望是用Hibernate），web层控制器的servlet有两个选择，一个是用Struts，另一个是Spring的MVC。

以下是自己的阅读体会，也许分析不当或描述不清，但也算初步尝试，所以记下来了。

一，分层结构

Jpetstore使用了门面模式、单例模式，DAO模式。

1.门面模式

门面接口的实现类： PetStoreImpl

public class PetStoreImpl 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;

    }

    //省略余下的四个setter

    // -------------------------------------------------------------------------

    // 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);

    }

    //省略其它的crud方法

}

暂时先不管 OrderService 这个接口。

PetStoreImpl的那些setter方法正是spring的注入方法。

在配置文件中：

<bean id="petStore" class="org.springframework.samples.jpetstore.domain.logic.PetStoreImpl">

    <property name="accountDao" ref="accountDao" />

    <property name="categoryDao" ref="categoryDao" />

    <property name="productDao" ref="productDao" />

    <property name="itemDao" ref="itemDao" />

    <property name="orderDao" ref="orderDao" />

</bean>

2. 单例模式

单例模式中，我们一般把类的构造方法设置为private，提供静态工厂方法给外界返回唯一的实例，但在这里，它不是这样做的，因为有了Spring。有了Spring的BeanFactory管理，可以轻易配置实现单例。看看作者的注释。

There is one instance of this class in the JPetStore application. In Spring terminology, it is a "singleton". This means a per-Application Context singleton. The factory creates a single instance; there is no need for a private constructor, static factory method etc as in the traditional implementation of the Singleton Design Pattern.

单例的PetStoreImpl

在Struts当控制器时，它这样做：为整个应用程序编写一个继承自Action的BaseAction基础类。

public abstract class BaseAction extends Action

{

    private PetStoreFacade petStore;

    public void setServlet(ActionServlet actionServlet)

    {

        super.setServlet(actionServlet);

        if (actionServlet != null)

        {

            ServletContext servletContext = actionServlet.getServletContext();

            WebApplicationContext wac = WebApplicationContextUtils

                .getRequiredWebApplicationContext(servletContext);

            this.petStore = (PetStoreFacade) wac.getBean("petStore");

        }

    }

    protected PetStoreFacade getPetStore()

    {

        return petStore;

    }

}

3.DAO模式

ORM工具用iBatis，在领域模式层使用了粗粒度对象。下面是AccountDao 的配置。

<select id="getAccountByUsername" resultMap="result">

    select

          signon.username as userid,

          account.email,

          account.firstname,

          account.lastname,

          account.status,

          account.addr1,

          account.addr2,

          account.city,

          account.state,

          account.zip,

          account.country,

          account.phone,

          profile.langpref,

          profile.favcategory,

          profile.mylistopt,

          profile.banneropt,

          bannerdata.bannername

    from account, profile, signon, bannerdata

    where account.userid = #value#

      and signon.username = account.userid

      and profile.userid = account.userid

      and profile.favcategory = bannerdata.favcategory

  </select>

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