> For the complete documentation index, see [llms.txt](https://fredhopper.gitbook.io/product-discovery/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://fredhopper.gitbook.io/product-discovery/a-b-testing-for-fhr/integration-steps-for-a-caching-solution/java-sdk-integration/extending-the-sdk.md).

# Extending the SDK

The **SDK** is designed to be easily extendable by providing custom implementations of the **RunningAbTestsFetcher** and **AbTestsCache** interfaces. Once provided to the **AbTesting** object through the **builder**, these will be called by the **AbTesting** object in the flow.

{% hint style="warning" %}
**Warning**! Custom implementations should only be if you absolutely need them. Rezolve AI can not offer support with integration of custom implementations.
{% endhint %}

The **interface** for **RunningAbTestsFetcher** can be imported as:

```
com.attraqt.sdk.fhr.abtesting.retrieval
```

And for **AbTestsCache** this can be imported as:

```
com.attraqt.sdk.fhr.abtesting.caching
```

Both rely on the model for **RunningAbTests** provided in the following location:

```
com.attraqt.sdk.fhr.abtesting.model;
```

Please ensure that the **A/B** tests server **URL** is **not** hit as part of any custom **AbTestsCache** implementation. **RunningAbTestsFetcher** implementations should take responsibility for fetching the **AB** tests, whereas **AbTestsCache** implementations should **only** be responsible for caching the **A/B** tests **provided** to **it**, rather than doing any calls to the server.

{% hint style="warning" %}
**Warning!** When doing a custom implementation, please make sure to respect the minimum refresh time of **5 minutes**, as otherwise we'd be forced to implement a throttling mechanism to avoid unnecessary load on our services.
{% endhint %}

Once the new object has been created, pass it to the **AbTestingBuilder** through the respective method (i.e. **abTestsCache** or **runningAbTestsFetcher**).