fix(EventSourceClient) : remove the need calling opPatch when incremental cache is off

- remove preconditions check if no cache
- update javadoc and demo

Author: bordigoni

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

@@ -45,7 +45,6 @@ public static void main(String... args) throws URISyntaxException, InterruptedEx
             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!"))
                     .open();
 

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

@@ -12,7 +12,6 @@ public interface EventSourceClient {
     String SD_PROXY_URL = "https://streamdata.motwin.net/";
 
 
-
     /**
      * Add a header to the polling request (those header will be passed to the request when SD.io will poll the API)
      *
@@ -88,7 +87,8 @@ public interface EventSourceClient {
 
 
     /**
-     * Opens the connections with streamdata proxy that will poll data for you. {@link #onSnapshot(Consumer)} and {@link #onPatch(Consumer)} must have called before.
+     * Opens the connections with streamdata proxy that will poll data for you.
+     * {@link #onSnapshot(Consumer)} must have called before and {@link #onPatch(Consumer)} is incremental cache is on (default is yes unless you call {@link #incrementalCache(boolean)} with false.
      *
      * @return a future to get hints on the thread status
      */

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

@@ -145,7 +145,9 @@ public JsonNode getCurrentSnapshot() {
     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()");
+        if (incrementalCache) {
+            checkNotNull(this.onPatchCallback, "You must call onPatch() with a non-null callback before calling open()");
+        }
         checkArgument(this.eventSource == null, "You cannot call open() on an already opened event source");
 
         try {