feat: add SpringValueCache for easy creation of ValueCache that use S…

…pring Caches

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

@@ -0,0 +1,76 @@
+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 java.util.function.Function;
+import lombok.RequiredArgsConstructor;
+import org.dataloader.ValueCache;
+import org.springframework.cache.Cache;
+import org.springframework.cache.Cache.ValueWrapper;
+
+/**
+ * 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;
+  private Function<K, ?> keyTransformer;
+
+  @Override
+  public CompletableFuture<V> get(K key) {
+    return supplyAsync(() -> {
+      Object finalKey = this.getKey(key);
+      ValueWrapper valueWrapper = this.cache.get(finalKey);
+
+      if (valueWrapper == null) {
+        throw new CacheEntryNotFoundException(this.cache.getName(), finalKey);
+      }
+
+      return (V) valueWrapper.get();
+    });
+  }
+
+  @Override
+  public CompletableFuture<V> set(K key, V value) {
+    return supplyAsync(() -> {
+      this.cache.put(this.getKey(key), value);
+      return value;
+    });
+  }
+
+  @Override
+  public CompletableFuture<Void> delete(K key) {
+    return runAsync(() -> this.cache.evictIfPresent(this.getKey(key)));
+  }
+
+  @Override
+  public CompletableFuture<Void> clear() {
+    return runAsync(this.cache::invalidate);
+  }
+
+  public <KFinal> SpringValueCache<K, V> setKeyTransformer(Function<K, KFinal> transformer) {
+    this.keyTransformer = transformer;
+    return this;
+  }
+
+  private Object getKey(K key) {
+    return (
+      this.keyTransformer == null
+        ? key
+        : this.keyTransformer.apply(key)
+    );
+  }
+
+  public static class CacheEntryNotFoundException extends RuntimeException {
+    public CacheEntryNotFoundException(String cacheName, Object key) {
+      super("Entry could not be found in cache named \"" + cacheName + "\" for key: " + key);
+    }
+  }
+}