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diff --git a/java/com/google/gerrit/server/git/RefCache.java b/java/com/google/gerrit/server/git/RefCache.java
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+// Copyright (C) 2016 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.gerrit.server.git;
+
+import java.io.IOException;
+import java.util.Optional;
+import org.eclipse.jgit.lib.ObjectId;
+
+/**
+ * Simple short-lived cache of individual refs read from a repo.
+ *
+ * <p>Within a single request that is known to read a small bounded number of refs, this class can
+ * be used to ensure a consistent view of one ref, and avoid multiple system calls to read refs
+ * multiple times.
+ *
+ * <p><strong>Note:</strong> Implementations of this class are only appropriate for short-term
+ * caching, and do not support invalidation. It is also not threadsafe.
+ */
+public interface RefCache {
+  /**
+   * Get the possibly-cached value of a ref.
+   *
+   * @param refName name of the ref.
+   * @return value of the ref; absent if the ref does not exist in the repo. Never null, and never
+   *     present with a value of {@link ObjectId#zeroId()}.
+   */
+  Optional<ObjectId> get(String refName) throws IOException;
+}