1 files changed, 44 insertions, 0 deletions
diff --git a/vespa-feed-client-api/src/main/java/ai/vespa/feed/client/Helper.java b/vespa-feed-client-api/src/main/java/ai/vespa/feed/client/Helper.java
index 59c12077bef..6971b2ea8f5 100644
--- a/vespa-feed-client-api/src/main/java/ai/vespa/feed/client/Helper.java
+++ b/vespa-feed-client-api/src/main/java/ai/vespa/feed/client/Helper.java
@@ -1,18 +1,62 @@
 // Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
 package ai.vespa.feed.client;
 
+import java.lang.reflect.Constructor;
+import java.lang.reflect.InvocationTargetException;
 import java.util.ArrayList;
+import java.util.Iterator;
 import java.util.List;
 import java.util.Objects;
+import java.util.ServiceLoader;
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.CompletionException;
+import java.util.concurrent.atomic.AtomicReference;
+import java.util.function.Supplier;
 import java.util.stream.Collectors;
 
+import static ai.vespa.feed.client.FeedClientBuilder.PREFERRED_IMPLEMENTATION_PROPERTY;
+
 /**
  * @author bjorncs
  */
 class Helper {
 
+    private static final AtomicReference<Supplier<FeedClientBuilder>> feedClientBuilderSupplier = new AtomicReference<>(Helper::getFeedClientBuilder);
+
+    static final void setFeedClientBuilderSupplier(Supplier<FeedClientBuilder> supplier) {
+        feedClientBuilderSupplier.set(supplier);
+    }
+
+    static Supplier<FeedClientBuilder> getFeedClientBuilderSupplier() {
+        return feedClientBuilderSupplier.get();
+    }
+
+    static FeedClientBuilder getFeedClientBuilder() {
+        String defaultImplementation = "ai.vespa.feed.client.impl.FeedClientBuilderImpl";
+        String preferredImplementation = System.getProperty(PREFERRED_IMPLEMENTATION_PROPERTY, defaultImplementation);
+        Iterator<FeedClientBuilder> iterator = ServiceLoader.load(FeedClientBuilder.class).iterator();
+        if (iterator.hasNext()) {
+            List<FeedClientBuilder> builders = new ArrayList<>();
+            iterator.forEachRemaining(builders::add);
+            return builders.stream()
+                    .filter(builder -> preferredImplementation.equals(builder.getClass().getName()))
+                    .findFirst()
+                    .orElse(builders.get(0));
+        } else {
+            try {
+                Class<?> aClass = Class.forName(preferredImplementation);
+                for (Constructor<?> constructor : aClass.getConstructors()) {
+                    if (constructor.getParameterTypes().length == 0) {
+                        return ((FeedClientBuilder) constructor.newInstance());
+                    }
+                }
+                throw new RuntimeException("Could not find Feed client builder implementation");
+            } catch (ClassNotFoundException | InvocationTargetException | InstantiationException | IllegalAccessException e) {
+                throw new RuntimeException(e);
+            }
+        }
+    }
+
     private Helper() {}
 
     @SafeVarargs