Add GraphQL subscription client example

Author: rogelio-o

web-graphql-examples/src/main/java/io/vertx/example/web/graphql/SubscriptionClient.java

@@ -0,0 +1,40 @@
+package io.vertx.example.web.graphql;
+
+import io.vertx.core.AbstractVerticle;
+import io.vertx.core.Launcher;
+import io.vertx.core.http.HttpClient;
+import io.vertx.core.http.HttpClientOptions;
+import io.vertx.core.http.WebSocket;
+import io.vertx.core.json.JsonObject;
+import io.vertx.ext.web.handler.graphql.ApolloWSMessageType;
+
+public class SubscriptionClient extends AbstractVerticle {
+
+  public static void main(String[] args) {
+    Launcher.executeCommand("run", SubscriptionClient.class.getName());
+  }
+
+  @Override
+  public void start() {
+    HttpClient httpClient = vertx.createHttpClient(new HttpClientOptions().setDefaultPort(8080));
+    httpClient.webSocket("/graphql").setHandler(websocketRes -> {
+      if (websocketRes.succeeded()) {
+        WebSocket webSocket = websocketRes.result();
+
+        webSocket.handler(message -> {
+          System.out.println(message.toJsonObject().encodePrettily());
+        });
+
+        JsonObject request = new JsonObject()
+          .put("id", "1")
+          .put("type", ApolloWSMessageType.START.getText())
+          .put("payload", new JsonObject()
+            .put("query", "subscription { links { url, postedBy { name } } }"));
+        webSocket.write(request.toBuffer());
+      } else {
+        websocketRes.cause().printStackTrace();
+      }
+    });
+  }
+
+}