Expose getter to return values stored in the SharedRefDB

Feature: Issue 12251
Change-Id: Ic997c13f75c0bf30f25a5082b8fecee86186414e

src/main/java/com/gerritforge/gerrit/globalrefdb/GlobalRefDatabase.java

diff --git a/src/main/java/com/gerritforge/gerrit/globalrefdb/GlobalRefDatabase.java b/src/main/java/com/gerritforge/gerrit/globalrefdb/GlobalRefDatabase.java
index c2e222b..4217751 100644
--- a/src/main/java/com/gerritforge/gerrit/globalrefdb/GlobalRefDatabase.java
+++ b/src/main/java/com/gerritforge/gerrit/globalrefdb/GlobalRefDatabase.java
@@ -15,6 +15,7 @@
 package com.gerritforge.gerrit.globalrefdb;
 
 import com.google.gerrit.reviewdb.client.Project;
+import java.util.Optional;
 import org.eclipse.jgit.lib.ObjectId;
 import org.eclipse.jgit.lib.Ref;
 
@@ -81,4 +82,14 @@
    * @throws GlobalRefDbSystemError project cannot be removed due to a system error.
    */
   void remove(Project.NameKey project) throws GlobalRefDbSystemError;
+
+  /**
+   * Return value for a specific project and ref name
+   *
+   * @param project project name
+   * @param refName reference name
+   * @return {@link java.util.Optional} of the value
+   * @throws GlobalRefDbSystemError value cannot be returned due to a system error.
+   */
+  <T> Optional<T> get(Project.NameKey project, String refName) throws GlobalRefDbSystemError;
 }

src/test/java/com/gerritforge/gerrit/globalrefdb/FakeGlobalRefDatabase.java

diff --git a/src/test/java/com/gerritforge/gerrit/globalrefdb/FakeGlobalRefDatabase.java b/src/test/java/com/gerritforge/gerrit/globalrefdb/FakeGlobalRefDatabase.java
index 498cd76..d96f532 100644
--- a/src/test/java/com/gerritforge/gerrit/globalrefdb/FakeGlobalRefDatabase.java
+++ b/src/test/java/com/gerritforge/gerrit/globalrefdb/FakeGlobalRefDatabase.java
@@ -16,6 +16,7 @@
 
 import com.google.common.collect.MapMaker;
 import com.google.gerrit.reviewdb.client.Project;
+import java.util.Optional;
 import java.util.concurrent.ConcurrentMap;
 import java.util.concurrent.atomic.AtomicReference;
 import java.util.concurrent.locks.Lock;
@@ -86,6 +87,14 @@
     keyValueStore.remove(project);
   }
 
+  @Override
+  @SuppressWarnings("unchecked")
+  public <T> Optional<T> get(Project.NameKey project, String refName)
+      throws GlobalRefDbSystemError {
+    return Optional.ofNullable((T) projectRefDb(project).get(refName))
+        .map(v -> ((AtomicReference<T>) v).get());
+  }
+
   private ConcurrentMap<String, AtomicReference<ObjectId>> projectRefDb(Project.NameKey project) {
     ConcurrentMap<String, AtomicReference<ObjectId>> projectRefDb = keyValueStore.get(project);
     if (projectRefDb == null) {

src/test/java/com/gerritforge/gerrit/globalrefdb/GlobalRefDatabaseTest.java

diff --git a/src/test/java/com/gerritforge/gerrit/globalrefdb/GlobalRefDatabaseTest.java b/src/test/java/com/gerritforge/gerrit/globalrefdb/GlobalRefDatabaseTest.java
index b1bad65..9e2ee81 100644
--- a/src/test/java/com/gerritforge/gerrit/globalrefdb/GlobalRefDatabaseTest.java
+++ b/src/test/java/com/gerritforge/gerrit/globalrefdb/GlobalRefDatabaseTest.java
@@ -18,6 +18,7 @@
 
 import com.google.gerrit.acceptance.AbstractDaemonTest;
 import com.google.gerrit.reviewdb.client.RefNames;
+import java.util.Optional;
 import java.util.concurrent.Executor;
 import java.util.concurrent.Executors;
 import org.eclipse.jgit.lib.ObjectId;
@@ -152,6 +153,20 @@
     }
   }
 
+  @Test
+  public void shouldReturnValueInTheGlobalRefDB() {
+    objectUnderTest.compareAndPut(project, initialRef, objectId1);
+    Optional<ObjectId> o = objectUnderTest.get(project, initialRef.getName());
+    assertThat(o.isPresent()).isTrue();
+    assertThat(o.get()).isEqualTo(objectId1);
+  }
+
+  @Test
+  public void shouldReturnEmptyIfValueIsNotInTheGlobalRefDB() {
+    Optional<ObjectId> o = objectUnderTest.get(project, "nonExistentRef");
+    assertThat(o.isPresent()).isFalse();
+  }
+
   private Ref ref(String refName, ObjectId objectId) {
     return new ObjectIdRef.Unpeeled(Ref.Storage.NETWORK, refName, objectId);
   }