Hi Amit,
Here the Username input is taken from the key field of the business object.
So you need to pass the value to the "USERNAME" field in the business object, so the method GETDETAIL will fetch the data for that username in the key field..
In the workflow you need to create a workflow container with type reference to business object,then you need to pass the value to the Username field in the business object and also you need to create a container in task and you need to bind it with workflow container.
Regards,
KK