Finally, it is time to create the implementation for the HelloWorldMediation component. This component is a mediation flow and was created for you when you created the mediation module, although you could also create one by dragging a mediation flow from the palette. Because of the type of the component, you will use the mediation flow editor to implement it.
In the flow area, you see an input node on the left, which represents control reaching your request flow by way of the callHello operation being invoked. On the right, there are two output nodes: the top one, which represents calling out to the getHello reference operation and the bottom one that represents returning to the caller of this flow. If you wire to the top callout output node, you will invoke whatever that reference is wired to, which in this case is an external Web service. If you wire to the bottom input response output node, you will end the flow and send a response back to whatever is wired to this component, which in this case is an SCA export component. However, typically the result is returned in the response flow versus this input response node.
The flow editor allows you to place primitives between the input and output nodes and wire them together, producing a flow upon which the message travels. The message is the parameter data for the input operation, which in this case is the payload for callHello – namely, a FullName business object.
The warning occurs because you have not dealt with the case when the call to the Web service fails. Expand the Error Handling category in the palette, and drag the Fail primitive to the canvas, and then wire the Callout Response fail terminal to this primitive. Then from the context menu of the Fail primitive, select Show in Properties. Go to the Details property page and enter a string like “Oops, call failed!” to include in the fault that gets sent to the caller, as shown in the following figure: