Interface ResponseObserver<V> (2.55.0)

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public interface ResponseObserver<V>

Receives notifications from server-streaming calls.

The application is responsible for implementing the ResponseObserver and passing it to GAX, which then calls the observer with the messages for the application to receive them. The methods might be called by different threads, but are guaranteed to happen sequentially. The order of callbacks is guaranteed to be:

• exactly 1 onStart
• 0 or more on Response
• exactly 1 onError or onComplete

By default, the stream uses automatic flow control, where the next response will be delivered as soon as the current one is processed by onResponse. A consumer can disable automatic flow control by calling disableAutoInboundFlowControl() in onStart. After this, the consumer must request responses by calling request().

Type Parameter
Name	Description
V

Methods

onComplete()

public abstract void onComplete()

Receives a notification of successful stream completion.

May only be called once, and if called, it must be the last method called. In particular, if an exception is thrown by an implementation of onComplete, no further calls to any method are allowed.

onError(Throwable t)

public abstract void onError(Throwable t)

Receives a terminating error from the stream.

May only be called once, and if called, it must be the last method called. In particular, if an exception is thrown by an implementation of onError, no further calls to any method are allowed.

Parameter
Name	Description
t	Throwable the error occurred on the stream

onResponse(V response)

public abstract void onResponse(V response)

Receives a value from the stream.

Can be called many times but is never called after #onError(Throwable) or #onComplete() are called.

Clients may may receive 0 or more onResponse callbacks.

If an exception is thrown by an implementation the caller will terminate the stream by calling #onError(Throwable) with the caught exception as the cause.

Parameter
Name	Description
response	V the value passed to the stream

onStart(StreamController controller)

public abstract void onStart(StreamController controller)

Called before the stream is started. This must be invoked synchronously on the same thread that called ServerStreamingCallable#call(Object, ResponseObserver, ApiCallContext)

Allows for disabling flow control and early stream termination via StreamController.

Parameter
Name	Description
controller	StreamController The controller for the stream.