refactor(EventSourceClient) : change some return types

- Remove unused Future as return type
- add EventSourceClient as return type of open()
- update demo code

Author: bordigoni

src/main/java/io/streamdata/demo/Main.java

@@ -42,8 +42,8 @@ public static void main(String... args) throws URISyntaxException, InterruptedEx
          * */
         {
 
-            EventSourceClient eventSource = StreamdataClient.createClient(apiURL, appKey);
-            eventSource.incrementalCache(false)
+            EventSourceClient eventSource = StreamdataClient.createClient(apiURL, appKey)
+                    .incrementalCache(false)
                     .onSnapshot(data -> logger.info("INITIAL SNAPSHOT {}", data))
                     .onPatch(System.out::println) // useless
                     .onOpen(() -> logger.info("And we are... live!"))

src/main/java/io/streamdata/sdk/EventSourceClient.java

@@ -2,7 +2,6 @@
 
 import com.fasterxml.jackson.databind.JsonNode;
 
-import java.util.concurrent.Future;
 import java.util.function.Consumer;
 
 /**
@@ -93,7 +92,7 @@ public interface EventSourceClient {
      *
      * @return a future to get hints on the thread status
      */
-    Future<?> open();
+    EventSourceClient open();
 
     /**
      * Closes the event source gracefully

src/main/java/io/streamdata/sdk/impl/EventSourceClientImpl.java

@@ -21,7 +21,6 @@
 import java.net.URI;
 import java.net.URISyntaxException;
 import java.net.URLEncoder;
-import java.util.concurrent.Future;
 import java.util.concurrent.atomic.AtomicReference;
 import java.util.function.Consumer;
 
@@ -143,7 +142,7 @@ public JsonNode getCurrentSnapshot() {
 
 
     @Override
-    public Future<?> open() {
+    public EventSourceClient open() {
 
         checkNotNull(this.onDataCallback, "You must call onSnapshot() with a non-null callback before calling open()");
         checkNotNull(this.onPatchCallback, "You must call onPatch() with a non-null callback before calling open()");
@@ -234,7 +233,7 @@ public void onEvent(InboundEvent inboundEvent) {
             System.exit(1);
         }
 
-        return null;
+        return this;
 
 
     }