Channels are client-side objects that encapsulate the connection behavior between Flex components and the BlazeDS server. Channels communicate with corresponding endpoints on the BlazeDS server. You configure the properties of a channel and its corresponding endpoint in the services-config.xml file.

信道是链接flex components和blazeds服务的客户端对象，信道可以与在BlazeDs服务器上的终端进行通信，你可以在services-config.xml文件中配置信道与它对象的终端

Configuring channels and endpoints

配置信道和终端

You configure channels in channel definitions in the services-config.xml file. The channel definition in the following example creates an AMFChannel that communicates with an AMFEndpoint on the server:

你可以在services-config.xml中以通道定义的方式配置通道.在下面的例子中的通道可以产生一个AMFChannel与服务器上的AMFEndpoint进行通信。

<channels>
...
<channel-definition id="samples-amf"
        type="mx.messaging.channels.AMFChannel">
        <endpoint url="http://servername:8400/myapp/messagebroker/amf"
            type="flex.messaging.endpoints.AMFEndpoint"/>
</channel-definition>
</channels>

The channel-definition element specifies the following information:

该通道定义元素指定如下信息：

• id and channel class type of the client-side channel that the Flex client uses to contact the server
• id和type属性指定与服务器进行通信的客户端信道类型
• endpoint element that contains the URL and endpoint class type of the server-side endpoint
• 终端元素包含服务器的URL和type属性
• properties element that contains channel and endpoint properties
• 属性元素包含信道和终端的属性?

The endpoint URL is the specific network location that the endpoint is exposed at. The channel uses this value to connect to the endpoint and interact with it. The URL

终端URL是终端所在的确定网络地址。信道使用该值与终端进行链接和通信。在所有服务器产生的终端中这个URL必须是唯一的。这个URL属性指向MessageBrokerServlet

?must be unique across all endpoints exposed by the server. The url attribute points to the MessageBrokerServlet.

How channels are assigned to a Flex component

信道是如何被分配给flex组件

Flex components use channel sets,which contain one or more channels,to contact the server. You can automatically or manually create and assign a channel set to a

flex组件使用信道组(信道组包含一个或者多个信道)与服务器进行通信，你可以自动或者手动创建和分配一个信道给flex组件

Flex component. The channel allows the component to contact the endpoint,which forwards the request to the destination.

该信道允许组件与终端进行链接，从而将请求发送到目的地

If you compile an MXML file using the MXML compiler option -services pointing to the services-config.xml file,the component (RemoteObject,HTTPService,and so on)

如果你编译一个MXML文件指定了选项 -services 对应的services-config.xml文件，那么组件(RemoteObject,HTTPService等等)将被自动分配一个信道组，is automatically assigned a channel set that contains one or more appropriately configured channel instances. The configuration is based on the channel definition

该信道组包含一个或者多个适合配置好的信道实例。该配置是建立在信道定义基础上的，在配置文件中分配了一个目的地。或者，如果你没有在编译环境中使用-service选项

assigned to a destination in a configuration file. Alternatively,if you do not compile your application with the -services option or want to override the compiled-in

，想重写编译行为，你可以手动创建一个信道组在MXML或者ActionScript,分配一个或者多个信道，然后将该信道组指定给flex?组件

behavior,you can manually create a channel set in MXML or ActionScript,populate it with one or more channels,and then assign the channel set to the Flex component.

Application-level default channels are especially important when you want to use dynamically created destinations and you do not want to create and assign channel sets

当你想手动创建应用目的地，并且不想为你的动态目的地的flex?组件创建和分配信道组，那么应用级别的信道对这种应用是很重要的

to your Flex components that use the dynamic destination. In that case,application-level default channels are used. For more information,see Assigning channels and endpoints to a destination.

这种情况时应用级别的默认信道应该被使用。需要更多信息可以查看为目的地分配信道和终端

When you compile a Flex client application with the MXML compiler-services option,it contains all of the information from the configuration files that is needed for the client to connect to the server.

当你编译一个flex客户端应用带有编译环境-services选项，它包含客户端与服务端进行链接的所有必要配置信息

To manually create channels,you create your own channel set in MXML or ActionScript,add channels to it,and then assign the channel set to a component. This process

为了手动创建信道，你创建自己信道组在MXML或者ActionScript文件，在其中添加信道，然后分配在信道组给对应的组件，这个过程一般遵循如下的规则：

is common in the following situations:

• You do not compile your MXML file using the -services MXML compiler option. This is useful when you do not want to hard code endpoint URLs into your compiled SWF files on the client.
• 你在编译环境中没有使用 -services选项，当你不想使用硬代码将终端URL嵌入到你的为客户端编译的SWF文件中
• You want to use a dynamically created destination (the destination is not in the services-config.xml file) with the run-time configuration feature. For more information,see Run-time configuration.
• 你希望动态创建目的地，该目的地不在services-config.xml文件中，带有运行时的配置特征，需要更多信息，请查看运行时配置
• You want to control in your client code the order of channels that a Flex component uses to connect to the server.
• 你希望在你的客户端代码控制信道序列，该信道进行flex组件与服务器的通信

When you create and assign a channel set on the client,the client requires the correct channel type and endpoint URL to contact the server. The client does not specify

当你在客户端创建和分配一个信道组，客户端需要一个正确的信道类型和终端URL与服务器进行连接，客户端没有指定终端类进行请求的处理

the endpoint class that handles that request,but there must be a channel definition in the services-config.xml file that specifies the endpoint class to use with the specified endpoint URL.

但是必须在services-config.xml文件中有一个信道定义，它指定终端类和所使用的确定终端URL

The following example shows a RemoteObject component that defines a channel set and channel inline in MXML:

下面的例子显示了一个RemoteObject组件，定义了一个信道组和内联信道在MXML文件中：

...
<RemoteObject id="ro" destination="Dest">
    <mx:channelSet>
        <mx:ChannelSet>
            <mx:channels>
                <mx:AMFChannel id="myAmf"
                    uri="http://myserver:2000/myapp/messagebroker/amf"/>
            </mx:channels>
        </mx:ChannelSet>
    </mx:channelSet>
</RemoteObject>
...

The following example shows ActionScript code that is equivalent to the MXML code in the previous example:

下面显示的as脚本与前面例子中的MXML代码具有一样作用:

...
    private function run():void {
            ro = new RemoteObject();
            var cs:ChannelSet = new ChannelSet(); 
            cs.addChannel(new AMFChannel("myAmf","http://servname:2000/eqa/messagebroker/amf"));
            ro.destination = "Dest"; 
            ro.channelSet = cs;
    }
...

Assigning channels and endpoints to a destination

分配一个信道和终端给一个目的地

Settings in the BlazeDS configuration files determine the channels and endpoints from which a destination can accept messages,invocations,or data,except when you use the run-time configuration feature. The channels and endpoints are determined in one of the following ways:

在BlazeDS配置文件中的设置决定了从哪个信道组和终端中目的地地址可以接收到消息，头信息，数据，排除使用运行配置的这种情况。这些信道和终端是以下面的方式被决定的

• If most of the destinations across all services use the same channels,you can define application-level default channels in the services-config.xml file,as the following example shows.

?????????? 如果多数的目的地跨越了所有服务使用一样的信道，那么定义一个应用级别的默认通道在services-config.xml文件中，如下面的例子所示：

<services-config ...>
...
    <default-channels>
        <channel ref="my-http"/>
        <channel ref="my-amf"/>
    </default-channels>
...

In this case,all destinations that do not define channels use a default channel. Destinations can override the default channel setting by specifying their own channels,and services can also override it by specifying their own default channels.

<service ...>
...
    <default-channels>
        <channel ref="my-http"/>
        <channel ref="my-amf"/>
    </default-channels>
...

<destination id="sampleVerbose">
    <channels>
        <channel ref="my-secure-amf"/>
    </channels>
...
</destination>