# Step 9 - Add a Standalone Activity

> For the complete documentation index, see [llms.txt](https://docs.temporal.io/llms.txt).
> Any documentation page is available as raw Markdown by appending `.md` to its URL.

> Back the notification Nexus Operation with a Standalone Activity instead of a Workflow, with no wrapper Workflow required.

The last Operation is `notifyRequester`, which tells the requester their approval was `APPROVED` or `DENIED`.

This one is not a Workflow. It is a single outbound notification with no state, nothing to wait for, and nothing to orchestrate — the [Standalone Activity](/nexus/standalone-activity) shape chosen in [step 3](/develop/java/nexus/development-walkthrough/choose-backing-implementation).

## Write the Activity

The Activity is an ordinary Activity. In this walkthrough it is a placeholder that does nothing — no email is sent. Real logic would call an email provider, push to a notification service, or write to an outbox.

Nothing in it is Nexus-specific. The same Activity Function can be invoked from a Workflow and started behind this Operation with no code changes — what differs is what starts it, not how it is written.

`{sample code will be here}`

## Back the Operation with it

Use `TemporalOperationHandler` as with every other Operation, but start an Activity on the [Client](/nexus/temporal-operation-handler#the-nexus-aware-client) instead of a Workflow. The Operation starts an Activity Execution with no parent Workflow and completes when the Activity returns.

This is the right shape whenever an Operation is one durable step behind a team boundary. The Activity supplies the durability — retries on the policy you set, timeouts you control, and a record of every attempt — and the Operation supplies the contract, so the notification is reachable by other teams without them sharing your code or your Namespace.

`{sample code will be here}`

### Options an Activity-backed Operation requires

`StartActivityOptions` needs an **Activity Id**, unique within the Namespace, which a Workflow-called Activity does not, because there is no parent Workflow to scope it.

The Task Queue is optional and defaults to the one the Operation is running on. Set it explicitly to run notifications on their own Worker fleet rather than the one the Endpoint targets.

**To keep server retries from sending a second email, derive the Activity Id from the Nexus request Id.** The server retries Nexus start requests, and the request Id travels with them, so every retry lands on the same Activity Id and the notification goes out once. Without that, a retried request is a duplicate message to a real person.

The same pattern applies to any Operation whose work is externally visible and cannot be taken back: charging a card, posting to a webhook, creating a ticket, writing to a system with no dedup of its own. Deriving the Id from the request Id costs nothing and removes the whole class of duplicate-side-effect bugs.

Deriving the Id from the Operation *input* instead is a different tool for a different job: it makes several Operations share one Activity Execution and all receive its result. See [Nexus Standalone Activity](/nexus/standalone-activity#required-options).

## Register the Activity on the Worker

Add the Activity implementation to the same Worker that hosts the Nexus Service. An Activity-backed Operation needs no Workflow implementation registered for it.

`{sample code will be here}`

## Cancellation needs heartbeating

This notification finishes immediately, so cancellation never comes up for it. It does come up for any longer Activity-backed Operation, and the behavior differs from a Workflow-backed one: an Activity is not interrupted by a cancellation request, so an Activity that never heartbeats runs to completion or to its timeout no matter how many cancellations arrive.

If you write a long-running Activity-backed Operation, read [Activity cancellation](/activity-execution#cancellation) before you ship it. None of the mechanics are Nexus-specific.

## Next

**[Step 10 - Call the Standalone Activity](/develop/java/nexus/development-walkthrough/call-the-standalone-activity)** - complete the approval flow end to end.

Back to the [Microservice Development Walkthrough overview](/develop/java/nexus/development-walkthrough).

> **💡 Tip:**
> RESOURCES
>
> - [Nexus Standalone Activity](/nexus/standalone-activity) for the full concept and options.
> - [Standalone Activity](/standalone-activity) for Activity Executions outside a Workflow.
> - [Java: Standalone Activities](/develop/java/activities/standalone-activities) for the SDK API.
>