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EnterLib ObjectBuild vs Castle WindsorContainer, part 1

Posted on 2006-08-15 14:35 idior 阅读(...) 评论(...) 编辑 收藏
首先来看一下在Castle项目中用于示范其Ioc功能的一个小例子:


   1:  public interface IEmailSender
   2:  {
   3:      void Send(String from, String to, String message);
   4:  }
   5:   
   6:  public interface ITemplateEngine
   7:  {
   8:      String Process(String templateName);
   9:  }
  10:   
  11:  public interface INewsletterService
  12:  {
  13:      void Dispatch(String from, String[] targets, String message);
  14:  }
  15:   
  16:  public class SmtpEmailSender : IEmailSender
  17:  {
  18:      private String _host;
  19:      private int _port;
  20:   
  21:      public SmtpEmailSender(String host, int port)
  22:      {
  23:          _host = host;
  24:          _port = port;
  25:      }
  26:   
  27:      public virtual void Send(String from, String to, String message)
  28:      {
  29:          Console.WriteLine("Sending e-mail from {0} to {1} with '{2}'", 
  30:              from, to, message );
  31:      }
  32:  }
  33:   
  34:  public class NVelocityTemplateEngine : ITemplateEngine
  35:  {
  36:      public virtual String Process(String templateName)
  37:      {
  38:          return "Some template content";
  39:      }
  40:  }
  41:   
  42:  public class SimpleNewsletterService : INewsletterService
  43:  {
  44:      private IEmailSender _sender;
  45:      private ITemplateEngine _templateEngine;
  46:   
  47:      public SimpleNewsletterService
  48:          (IEmailSender sender, ITemplateEngine templateEngine)
  49:      {
  50:          _sender = sender;
  51:          _templateEngine = templateEngine;
  52:      }
  53:   
  54:      public void Dispatch(String from, String[] targets, String message)
  55:      {
  56:          String msg = _templateEngine.Process(message);
  57:   
  58:          foreach(String target in targets)
  59:          {
  60:              _sender.Send(from, target, msg);
  61:          }
  62:      }
  63:   
  64:  }


Ioc的作用就是能够利用容器自动的构建出一个SimpleNewsletterService对象,而不是由用户直接的创建并传递其参数,这样就可以进一步降低对象与对象之间耦合程度,从而方便的替换其实现。在上例中将采用构造器设值的方式,来实现对象依赖关系的注入。下面给出Castle的实现方式:

BasicUsage.xml
<?xml version="1.0" encoding="utf-8" ?>
<configuration>
    <components>
        <component id="smtpemailsender">
            <parameters>
                <host>localhost</host>
                <port>110</port>
            </parameters>
        </component>
    </components>
</configuration>

   1:  public static void Main()
   2:  {
   3:      IWindsorContainer container = 
   4:      new WindsorContainer( new XmlInterpreter("../BasicUsage.xml") );
   5:   
   6:      container.AddComponent( "newsletter", 
   7:          typeof(INewsletterService), typeof(SimpleNewsletterService) );
   8:      container.AddComponent( "smtpemailsender", 
   9:          typeof(IEmailSender), typeof(SmtpEmailSender) );
  10:      container.AddComponent( "templateengine", 
  11:          typeof(ITemplateEngine), typeof(NVelocityTemplateEngine) );
  12:   
  13:      String[] friendsList = new String[] { "john", "steve", "david" };
  14:   
  15:      // Ok, start the show
  16:   
  17:      INewsletterService service = 
  18:          (INewsletterService) container["newsletter"];
  19:      service.Dispatch("hammett at gmail dot com",
  20:                                friendsList, "merryxmas");
  21:  }

不断向容器中加入各种类型的对象,加入过程中容器自动建立起它们之间的依赖关系,最后当我们从容器取出对象的时候,就是已经配置好依赖关系的对象。以上就是Castle的工作模式,不过Castle中的配置过程过于透明,在你完全意料不到的情况下,对象的依赖关系就按照对象被注入容器的先后顺序被设定了。非常的自动,非常的透明带来的就是某些时候的莫名奇妙。

再来看看ObjectBuild的实现方式,首先你需要通过属性(Attibute)或者配置文件的方式显式的设定依赖关系:

  42:  public class SimpleNewsletterService : INewsletterService
  43:  {
  44:      private IEmailSender _sender;
  45:      private ITemplateEngine _templateEngine;
  46:   
  47:      public SimpleNewsletterService(
  48:              [Dependency(CreateType = typeof(SmtpEmailSender))]
  49:              IEmailSender sender, 
  50:              [Dependency(CreateType = typeof(NVelocityTemplateEngine))] 
  51:              ITemplateEngine templateEngine)
  52:      {
  53:          _sender = sender;
  54:          _templateEngine = templateEngine;
  55:      }
  56:   
  57:      public void Dispatch(String from, String[] targets, String message)
  58:      {
  59:          String msg = _templateEngine.Process(message);
  60:   
  61:          foreach(String target in targets)
  62:          {
  63:              _sender.Send(from, target, msg);
  64:          }
  65:      }
  66:   
  67:  

 

然后再利用Build直接的构造出对象

public static void Main(string[] args)
{
    string config = string.Format(
      @"<object-builder-config xmlns='pag-object-builder'>
        <build-rules>
            <build-rule type='{0}' mode='Singleton'>
              <mapped-type type='{1}'/>                           
              <constructor-params>
                 <value-param type='System.String'>localhost</value-param>
                 <value-param type='System.Int32'>110</value-param>
              </constructor-params>
            </build-rule>
         </build-rules>
        </object-builder-config>"
, FullNameIEmailSender, FullNameSmtpEmailSender);

    Builder builder = new Builder(ObjectBuilderXmlConfig.FromXml(config));
    Locator locator = CreateLocator();

    INewsletterService newsletterService =
       builder.BuildUp<SimpleNewsletterService>(locator, null, null);


    String[] friendsList = new String[] { "john", "steve", "david" };

    // Ok, start the show

    newsletterService.Dispatch("hammett at gmail dot com",
                                  friendsList, "merryxmas");
}

从以上我们可以看出
1.  ObjectBuild和Sping类似,需要显式指定依赖关系,不过多出通过Attribute来指定的方式,而Castle则依赖于特定的对象注入顺序。可以说各有优缺点,但是我prefer前者,安全第一。(Castle也提供了在配置文件中显式指定的方式。)
2.  ObjectBuild支持直接创建临时对象,而不注入容器。(注意在上面的代码中我们仅仅BuildUp了SimpleNewsletterService,而没有象Castle那样还要将SimpleNewsletterService所依赖的对象也注入容器。)其实在OB中你可以选择是否将对象注入容器,通常情况下Singleton类型的对象才被注入容器。
3.  相对与Castle容器的概念,ObjectBuild如同它的名字所示,更象是一个构建器,你可以通过它来构建任意的对象,这些对象可能会被注入容器,也可能仅仅是一个临时对象,不过在对象的创建过程中你可以加入很多的控制,让它更符合你的需求。
4. 相对而言Castle Ioc的使用更加简洁,而ObjectBuild更加复杂一些(其实比较它们构建对象所需要的语句,OB需要的更少,只是OB的API还不够简洁,需要再做些包装),不过ObjectBuild的定制扩展能力也是相当强大,比如以上通过配置文件和属性(Attribute)结合的配置方式,完全可以通过OB中提供的API搞定,下面就是采用全编程方式的实现:
    public static void Main()
    {

        Builder builder = new Builder();
        Locator locator = CreateLocator();
       
        builder.Policies.SetDefault<ISingletonPolicy>(new SingletonPolicy(true));
       
        ConstructorPolicy policy = new ConstructorPolicy();
        policy.AddParameter(new ValueParameter<string>("localhost"));
        policy.AddParameter(new ValueParameter<int>(110));

        builder.Policies.Set<ICreationPolicy>
            (policy, typeof(SmtpEmailSender), null);
        builder.Policies.Set<ITypeMappingPolicy>
            (new TypeMappingPolicy(typeof(SmtpEmailSender), null),
             typeof(IEmailSender), null);

        builder.Policies.Set<ITypeMappingPolicy>
            (new TypeMappingPolicy(typeof(NVelocityTemplateEngine), null),
             typeof(ITemplateEngine), null);

        ConstructorPolicy policy2 = new ConstructorPolicy();
        policy2.AddParameter(new CreationParameter(typeof(IEmailSender)));
        policy2.AddParameter(new CreationParameter(typeof(ITemplateEngine)));
        builder.Policies.Set<ICreationPolicy>
            (policy2,typeof(SimpleNewsletterService),null); 


        INewsletterService newsletterService =
             builder.BuildUp<SimpleNewsletterService>(locator, null, null);
     
        String[] friendsList = new String[] { "john", "steve", "david" };

        // Ok, start the show

        newsletterService.Dispatch("hammett at gmail dot com",
                                   friendsList, "merryxmas");
    }

5. Castle Ioc和ObjectBuild都支持属性设值(Property Setter)的注入方式,在此不再举例。