Support for Async Callbacks

Async callbacks allow a component to perform a request on another component and to receive its response asynchronously via a callback. This feature follows the programming model specified in the SCA Client and Implementation Model for Java (found in http://osoa.org/display/Main/Service+Component+Architecture+Specifications).

Currently, async callbacks are supported for components wired via bindless references, and via references with a web services binding using Axis2 (WS/Axis2).

Async Callbacks via Bindless References

In this mode, a source component uses a reference that does not include a binding, which is then wired to a target component via a service that does not include a binding either. For an example, see the inner.composite sample. To illustrate, an excerpt of the SCDLs for the inner.composite sample is as follows:

Source Composite

Contained in InnerComposite.scdl

• <component name="InnerSourceComponent">

  • <implementation.java class="innercomposite.SourceImpl"/>

  • <reference name="targetReference">TargetComponentRef</reference>

  </component>

  <reference name="TargetComponentRef">

  • <interface.java interface="innercomposite.Target"

    • callbackInterface="innercomposite.SourceCallback"/>

  </reference>

Target Composite

Contained in InnerComposite2.scdl

• <service name="InnerTargetService" target="InnerTargetComponent">

  • <interface.java interface="innercomposite.Target"

    • callbackInterface="innercomposite.SourceCallback"/>

    <reference name="innerSource">InnerTargetComponent</reference>

  </service>

  <component name="InnerTargetComponent">

  • <implementation.java class="innercomposite.TargetImpl"/>

  </component>

Containing Composite

Contained in default.scdl

• <component name="SourceComponent">

  • <implementation.composite name="InnerComposite" scdlLocation="InnerComposite.scdl"/> <reference name="TargetComponentRef2">TargetComponent2</reference>

  </component>

  <component name="TargetComponent2">

  • <implementation.composite name="InnerComposite2" scdlLocation="InnerComposite2.scdl"/>

  </component>

Async Callbacks via WS/Axis2 Binding

In this mode, the reference and service used by the source and target components use a WS/Axis2 binding (<binding.ws/>). For an example, see the helloworldws-async and helloworldwsclient-async samples. A preview of the SCDLs is as follows:

Server side

• <service name="HelloWorldWebService" target="http:///foo">

  • <interface.wsdl xmlns:wsdli="http://www.w3.org/2006/01/wsdl-instance"

    • interface="http://helloworld#wsdl.interface(HelloWorld)" callbackInterface="http://helloworld#wsdl.interface(HelloWorldCallback)" wsdli:wsdlLocation="http://helloworld wsdl/helloworld.wsdl" />

    <binding.ws endpoint="http://helloworld#wsdl.endpoint(HelloWorldService/HelloWorldSoapPort)"

    • conformanceURIs="http://ws-i.org/profiles/basic/1.1" location="wsdl/helloworld.wsdl" />

    <reference>HelloWorldServiceComponent</reference>

  </service>

  <component name="HelloWorldServiceComponent">

  • <implementation.java class="helloworld.HelloWorldImpl" />

  </component>

Client side

• <component name="HelloWorldServiceComponent">

  • <implementation.java class="helloworld.HelloWorldServiceComponent"/> <reference name="helloWorldService">HelloWorldService</reference>

  </component>

  <reference name="HelloWorldService">

  • <interface.wsdl xmlns:wsdli="http://www.w3.org/2006/01/wsdl-instance"

    • interface="http://helloworld#wsdl.interface(HelloWorld)" callbackInterface="http://helloworld#wsdl.interface(HelloWorldCallback)" wsdli:wsdlLocation="http://helloworld wsdl/helloworld.wsdl" />

    <binding.ws endpoint="http://helloworld#wsdl.endpoint(HelloWorldService/HelloWorldSoapPort)"

    • location="wsdl/helloworld.wsdl" />

  </reference>

Limitations

Currently, async callbacks over WS/Axis2 has the following limitations:

• The callback interface can only use a single method
• The WSDL definition in use must include a port type that describes the callback interface separately, see resources/META-INF/wsdl/helloworld.wsdl