# Interceptors

> 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.
> For related questions, query https://docs.temporal.io/api/retrieve?q=<question>&jtb=<job-to-be-done>&src=md-page&agent=<your-name> (no auth; returns JSON `{content, source_url, page_url}`, with `source_url` pointing to Markdown for docs pages). Don't include personal data or credentials.

Interceptors wrap inbound and outbound Temporal calls so you can apply shared behavior such as tracing, logging, or
authorization. See [Interceptors](/encyclopedia/interceptors) for the inbound vs outbound model.

Register them on the Client (`WorkflowClientOptions.Builder.setInterceptors`) or the Worker Factory
(`WorkerFactoryOptions.Builder.setWorkerInterceptors`). Full API:
[`io.temporal.common.interceptors`](https://www.javadoc.io/doc/io.temporal/temporal-sdk/latest/io/temporal/common/interceptors/package-summary.html).

Several interceptor APIs are marked `@Experimental`.

## Implement a Client interceptor

Extend `WorkflowClientInterceptorBase` and override `workflowClientCallsInterceptor` to return a
`WorkflowClientCallsInterceptor` that wraps `next`. Override only the calls you want to intercept; forward the rest to
`next` (or to `super`, if you extend `WorkflowClientCallsInterceptorBase`).

```java
public class TracingClientInterceptor extends WorkflowClientInterceptorBase {
  @Override
  public WorkflowClientCallsInterceptor workflowClientCallsInterceptor(
      WorkflowClientCallsInterceptor next) {
    return new WorkflowClientCallsInterceptorBase(next) {
      @Override
      public WorkflowStartOutput start(WorkflowStartInput input) {
        System.out.println("starting workflow " + input.getWorkflowId());
        return super.start(input);
      }
    };
  }
}
```

Register the interceptor when you build the Client:

```java
WorkflowClientOptions clientOptions =
    WorkflowClientOptions.newBuilder().setInterceptors(new TracingClientInterceptor()).build();
WorkflowClient client = WorkflowClient.newInstance(service, clientOptions);
```

## Implement a Worker interceptor

Extend `WorkerInterceptorBase` and override `interceptWorkflow`, `interceptActivity`, or both, for the inbound call
chains you need. Each inbound interceptor must forward every override to `next`. To also intercept outbound calls made
from inside the Workflow, wrap the `WorkflowOutboundCallsInterceptor` passed to `init` and forward that wrapper to
`next.init(...)`:

```java
public class TracingWorkerInterceptor extends WorkerInterceptorBase {
  @Override
  public WorkflowInboundCallsInterceptor interceptWorkflow(WorkflowInboundCallsInterceptor next) {
    return new WorkflowInboundCallsInterceptorBase(next) {
      @Override
      public void init(WorkflowOutboundCallsInterceptor outboundCalls) {
        next.init(
            new WorkflowOutboundCallsInterceptorBase(outboundCalls) {
              @Override
              public <R> ActivityOutput<R> executeActivity(ActivityInput<R> input) {
                Workflow.getLogger(TracingWorkerInterceptor.class)
                    .info("starting activity " + input.getActivityName());
                return super.executeActivity(input);
              }
            });
      }
    };
  }
}
```

Register the interceptor on the Worker Factory:

```java
WorkerFactoryOptions factoryOptions =
    WorkerFactoryOptions.newBuilder().setWorkerInterceptors(new TracingWorkerInterceptor()).build();
WorkerFactory factory = WorkerFactory.newInstance(client, factoryOptions);
```

> **⚠️ Warning:**
> Workflow interceptors and replay
>
> Workflow interceptor methods also run during [replay](/develop/java/best-practices/testing-suite#replay). Use replay-safe
> APIs for logging, randomness, and time.
>

## Related

- [Observability - Tracing](/develop/java/platform/observability#tracing)
- [Error handling - Worker Interceptor](/develop/java/best-practices/error-handling#centralize-with-interceptor)
- [Spring Boot - Interceptors](/develop/java/integrations/spring-boot-integration#interceptors)
- [Plugins - Interceptors](/develop/plugins-guide#interceptors)