By default, when a connection the 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 the any send 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. 
...
SSE event source will automatically schedule a new reconnect attempt and use the received {@value javax.ws.rs.core.HttpHeaders#RETRY_AFTER} HTTP header
value as a one-time override of the reconnect delay