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Step 6 - Call the Service

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Call requestApproval from a Workflow in the caller Namespace. The caller knows the Endpoint name and the contract, and nothing else about the handler.

Use the generated interface as a stub​

In Java, the generated Service interface works directly as a Nexus Service stub. Create it inside the caller Workflow with the Endpoint name and Operation options, then call its methods as if they were local.

Because the stub is the generated interface, the call is type-checked against the contract at compile time. A field the contract does not have will not compile, and a payload the contract forbids is rejected by the generated validator before it reaches the wire.

{sample code will be here}

Await the decision​

requestApproval returns APPROVED or DENIED. That value is the approval Workflow's return value, delivered to the caller through the Nexus completion callback when the Workflow finishes.

The caller does not poll. It awaits the Operation, and the wait is durable — the caller Workflow can be evicted, the Worker can restart, and the result still arrives.

Set a schedule-to-close timeout that reflects how long an approval can legitimately take. A human approval measured in days needs a timeout in days; the default is not going to be right. See Nexus Operations for the timeout model.

Callers in other languages​

The caller here is Java, but nothing about the handler requires that.

For reviewers

Every sample in this walkthrough is generated from the contract written in step 1, so a caller in any supported language talks to this same Java handler without changes on either side. Readers working in Go, Python, or TypeScript will be able to find a caller for their language in that language's sample repository rather than porting this one by hand.

To generate a caller for another language from this contract, see Generate code in the Nexus Client Code Generator documentation.

Calling without a caller Workflow​

A caller Workflow is the usual pattern and the one this walkthrough uses, because a Workflow gives the call durability and lets you orchestrate around it.

If you only need to run one Operation and have nothing to orchestrate, a Client can start an Operation directly with no caller Workflow at all. That is a Standalone Nexus Operation, and it uses the same Service contract, the same handler, and the same Endpoint — only the caller side differs. See Java: Standalone Operations.

Next​

The Service can start an approval and return a decision. Add messaging so callers can interact with an approval while it is pending.

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