added SpringValueCache for easy creation of data loader ValueCache ob…

…jects that utilize Spring Caches under the hood

graphql-kickstart-spring-support/src/main/java/graphql/kickstart/spring/cache/SpringValueCache.java

@@ -0,0 +1,43 @@
+package graphql.kickstart.spring.cache;
+
+import static java.util.concurrent.CompletableFuture.runAsync;
+import static java.util.concurrent.CompletableFuture.supplyAsync;
+
+import java.util.concurrent.CompletableFuture;
+import lombok.RequiredArgsConstructor;
+import org.dataloader.ValueCache;
+import org.springframework.cache.Cache;
+
+/**
+ * A {@link ValueCache} which uses a Spring {@link Cache} for caching.
+ *
+ * @see <a href="https://www.graphql-java.com/documentation/batching/#per-request-data-loaders">GraphQL Java docs</a>
+ */
+@RequiredArgsConstructor
+public class SpringValueCache<K, V> implements ValueCache<K, V> {
+
+  private final Cache cache;
+
+  @Override
+  public CompletableFuture<V> get(K key) {
+    return supplyAsync(() -> ((V) this.cache.get(key).get()));
+  }
+
+  @Override
+  public CompletableFuture<V> set(K key, V value) {
+    return supplyAsync(() -> {
+      this.cache.put(key, value);
+      return value;
+    });
+  }
+
+  @Override
+  public CompletableFuture<Void> delete(K key) {
+    return runAsync(() -> this.cache.evictIfPresent(key));
+  }
+
+  @Override
+  public CompletableFuture<Void> clear() {
+    return runAsync(this.cache::invalidate);
+  }
+}