How to design an agnostic api with enough modularity for specific implementations

Basically I have generic api for a series of datasources like the following:

api/data/get1
api/data/get2
api/data/get3

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The problem is how should this be designed when I want to implement a specific api for a datasource like the following:

 api/data/get1
 api/data/get2
 api/data/get3
 api/data/get4 - api specific to datasource

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I am using Spring Boot I have a package structure like the following:

services/
    dataservice/
        impl/
            dataserviceimpl

dataservice is an interface in this scenario

• dataservieimpl implements get1, get2, get3

  • my question is two-fold:
    • how do I implement a service specific to a datasource
    • what if I have multiple datasource which multiple apis specific to themselves

Thanks for reading