Interface SseEventSource

  • All Superinterfaces:

    public interface SseEventSource
    extends AutoCloseable
    Client for reading and processing incoming Server-Sent Events.

    SSE event source instances of this class are thread safe. To build a new instance, you can use the factory method to get a new event source builder that can be further customised and eventually used to create a new SSE event source.

    Once a SseEventSource is created, it can be used to open a connection to the associated web target. After establishing the connection, the event source starts processing any incoming inbound events. Whenever a new event is received, an Consumer<InboundSseEvent>#accept(InboundSseEvent) method is invoked on any registered event consumers.

    Reconnect support

    The SseEventSource supports automated recuperation from a connection loss, including negotiation of delivery of any missed events based on the last received SSE event id field value, provided this field is set by the server and the negotiation facility is supported by the server. In case of a connection loss, the last received SSE event id field value is sent in the "Last-Event-ID" HTTP request header as part of a new connection request sent to the SSE endpoint. Upon a receipt of such reconnect request, the SSE endpoint that supports this negotiation facility is expected to replay all missed events. Note however, that this is a best-effort mechanism which does not provide any guaranty that all events would be delivered without a loss. You should therefore not rely on receiving every single event and design your client application code accordingly.

    By default, when a connection to the SSE endpoint is lost, the event source will wait 500 ms before attempting to reconnect to the SSE endpoint. The SSE endpoint can however control the client-side retry delay by including a special retry field value in any sent event. JAX-RS SseEventSource tracks any received SSE event retry field values set by the endpoint and adjusts the reconnect delay accordingly, using the last received retry field value as the reconnect delay.

    In addition to handling the standard connection loss failures, JAX-RS SseEventSource behaves differently to various HTTP response status codes and headers:

    • 200 - with "Content-Type" header of "text/event-stream": This is normal operation. onEvent is invoked for each event. onComplete is invoked when there are no more events. onError is invoked only if an unrecoverable error occurs during processing.
    • 200 - with unsupported or missing "Content-Type" header: This is an error condition. onError is invoked.
    • 204 - This indicates that server has no events to send. Only onComplete is invoked.
    • 503 - with "Retry-After" header set to a valid value: This indicates that the server is unavailable, but that the client should reconnect later. No consumers are invoked unless the client event source is closed, prior to reconnecting (resulting in onComplete invocation). After the specified delay, the client should automatically attempt to reconnect which will result in a new response.
    • 503 - with invalid or missing "Retry-After" header: This is an error condition. onError is invoked.
    • Any other status code: This is an error condition. onError is invoked.

    In the case of an error condition response, the Throwable passed to the onError consumer should be a WebApplicationException containing the invalid Response object.

    Note that if, for any of the registered event consumers, an invocation of Consumer<InboundSseEvent>#accept(InboundSseEvent) method throws an exception, this is not an error condition. Thus onError is not invoked and event processing is not stopped. Users are encouraged to handle exceptions on their own as part of the event processing logic.

    Marek Potociar
    • Method Detail

      • register

        void register​(Consumer<InboundSseEvent> onEvent,
                      Consumer<Throwable> onError,
                      Runnable onComplete)
        Register InboundSseEvent and Throwable consumers and onComplete callback.

        Event consumer is invoked once per each received event, Throwable consumer is invoked invoked upon a unrecoverable error encountered by a SseEventSource, onComplete callback is invoked after a successful connection and when there are no further events to be received. Note that the onComplete callback will not be invoked if the onError callback has been invoked.

        onEvent - event consumer.
        onError - error consumer.
        onComplete - onComplete handler.
        IllegalArgumentException - when the any of the provided parameters is null.
      • target

        static SseEventSource.Builder target​(WebTarget endpoint)
        Create a new event source builder that provides convenient way how to configure and fine-tune various aspects of a newly prepared event source instance.
        endpoint - SSE streaming endpoint. Must not be null.
        a builder of a new event source instance pointing at the specified SSE streaming endpoint.
        NullPointerException - in case the supplied web target is null.
      • open

        void open()
        Open the connection to the supplied SSE underlying web target and start processing incoming events.
        IllegalStateException - in case the event source has already been opened earlier.
      • isOpen

        boolean isOpen()
        Check if this event source instance has already been opened.
        true if this event source is open, false otherwise.
      • close

        default void close()
        Close this event source.

        The method will wait up to 5 seconds for the internal event processing tasks to complete.

        Specified by:
        close in interface AutoCloseable
      • close

        boolean close​(long timeout,
                      TimeUnit unit)
        Close this event source and wait for the internal event processing task to complete for up to the specified amount of wait time.

        The method blocks until the event processing task has completed execution after a shutdown request, or until the timeout occurs, or the current thread is interrupted, whichever happens first.

        In case the waiting for the event processing task has been interrupted, this method restores the interrupt flag on the thread before returning false.

        timeout - the maximum time to wait.
        unit - the time unit of the timeout argument.
        true if this executor terminated and false if the timeout elapsed before termination or the termination was interrupted.