[hibernate#1001] Don't create a new Vert.x instance is one exists

DefaultVertxInstance used to create a new Vert.x instance
every time, even if one was already present.

This commit make it easier to use Hibernate Reactive when
a Vert.x instance already exists. In particular, when used
with Vert.x verticles.

Author: codingxu97

hibernate-reactive-core/src/main/java/org/hibernate/reactive/vertx/impl/DefaultVertxInstance.java

@@ -7,6 +7,7 @@
 
 import java.lang.invoke.MethodHandles;
 
+import io.vertx.core.Context;
 import io.vertx.core.Vertx;
 
 import org.hibernate.reactive.logging.impl.Log;
@@ -29,6 +30,7 @@ public final class DefaultVertxInstance implements VertxInstance, Stoppable, Sta
     private static final Log LOG = LoggerFactory.make( Log.class, MethodHandles.lookup() );
 
     private Vertx vertx;
+    private boolean vertxCreator;
 
     @Override
     public Vertx getVertx() {
@@ -40,14 +42,18 @@ public Vertx getVertx() {
 
     @Override
     public void stop() {
-        if ( vertx != null ) {
+        if ( vertxCreator && vertx != null ) {
             vertx.close().toCompletionStage().toCompletableFuture().join();
         }
     }
 
     @Override
     public void start() {
-        vertx = Vertx.vertx();
+        final Context context = Vertx.currentContext();
+        vertxCreator = context == null || context.owner() == null;
+        vertx = vertxCreator
+                ? Vertx.vertx() // Create a new one
+                : context.owner(); // Get the existing one
     }
 
 }