diff --git a/java/com/google/gerrit/server/restapi/change/GetRelated.java b/java/com/google/gerrit/server/restapi/change/GetRelated.java
index ba1a1dc..57291e8e 100644
--- a/java/com/google/gerrit/server/restapi/change/GetRelated.java
+++ b/java/com/google/gerrit/server/restapi/change/GetRelated.java
@@ -14,10 +14,6 @@
 
 package com.google.gerrit.server.restapi.change;
 
-import static com.google.common.base.Preconditions.checkArgument;
-import static java.util.stream.Collectors.toSet;
-
-import com.google.common.annotations.VisibleForTesting;
 import com.google.common.collect.Lists;
 import com.google.common.flogger.FluentLogger;
 import com.google.gerrit.common.Nullable;
@@ -29,56 +25,37 @@
 import com.google.gerrit.extensions.common.CommitInfo;
 import com.google.gerrit.extensions.restapi.Response;
 import com.google.gerrit.extensions.restapi.RestReadView;
-import com.google.gerrit.index.IndexConfig;
 import com.google.gerrit.server.ChangeUtil;
 import com.google.gerrit.server.CommonConverters;
-import com.google.gerrit.server.PatchSetUtil;
 import com.google.gerrit.server.change.RevisionResource;
-import com.google.gerrit.server.notedb.ChangeNotes;
 import com.google.gerrit.server.permissions.PermissionBackendException;
 import com.google.gerrit.server.project.NoSuchProjectException;
 import com.google.gerrit.server.query.change.ChangeData;
-import com.google.gerrit.server.query.change.InternalChangeQuery;
 import com.google.inject.Inject;
-import com.google.inject.Provider;
 import com.google.inject.Singleton;
 import java.io.IOException;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
 import java.util.Locale;
-import java.util.Set;
-import org.eclipse.jgit.errors.RepositoryNotFoundException;
 import org.eclipse.jgit.revwalk.RevCommit;
 
 @Singleton
 public class GetRelated implements RestReadView<RevisionResource> {
   private static final FluentLogger logger = FluentLogger.forEnclosingClass();
 
-  private final Provider<InternalChangeQuery> queryProvider;
-  private final PatchSetUtil psUtil;
-  private final RelatedChangesSorter sorter;
-  private final IndexConfig indexConfig;
   private final ChangeData.Factory changeDataFactory;
+  private final GetRelatedUtil getRelatedUtil;
 
   @Inject
-  GetRelated(
-      Provider<InternalChangeQuery> queryProvider,
-      PatchSetUtil psUtil,
-      RelatedChangesSorter sorter,
-      IndexConfig indexConfig,
-      ChangeData.Factory changeDataFactory) {
-    this.queryProvider = queryProvider;
-    this.psUtil = psUtil;
-    this.sorter = sorter;
-    this.indexConfig = indexConfig;
+  GetRelated(ChangeData.Factory changeDataFactory, GetRelatedUtil getRelatedUtil) {
     this.changeDataFactory = changeDataFactory;
+    this.getRelatedUtil = getRelatedUtil;
   }
 
   @Override
   public Response<RelatedChangesInfo> apply(RevisionResource rsrc)
-      throws RepositoryNotFoundException, IOException, NoSuchProjectException,
-          PermissionBackendException {
+      throws IOException, NoSuchProjectException, PermissionBackendException {
     RelatedChangesInfo relatedChangesInfo = new RelatedChangesInfo();
     relatedChangesInfo.changes = getRelated(rsrc);
     return Response.ok(relatedChangesInfo);
@@ -86,30 +63,15 @@
 
   public List<RelatedChangeAndCommitInfo> getRelated(RevisionResource rsrc)
       throws IOException, PermissionBackendException {
-    Set<String> groups = getAllGroups(rsrc.getNotes(), psUtil);
-    logger.atFine().log("groups = %s", groups);
-    if (groups.isEmpty()) {
-      return Collections.emptyList();
-    }
-
-    List<ChangeData> cds =
-        InternalChangeQuery.byProjectGroups(
-            queryProvider, indexConfig, rsrc.getChange().getProject(), groups);
-    if (cds.isEmpty()) {
-      return Collections.emptyList();
-    }
-    if (cds.size() == 1 && cds.get(0).getId().equals(rsrc.getChange().getId())) {
-      return Collections.emptyList();
-    }
-    List<RelatedChangeAndCommitInfo> result = new ArrayList<>(cds.size());
-
     boolean isEdit = rsrc.getEdit().isPresent();
     PatchSet basePs = isEdit ? rsrc.getEdit().get().getBasePatchSet() : rsrc.getPatchSet();
     logger.atFine().log("isEdit = %s, basePs = %s", isEdit, basePs);
 
-    cds = reloadChangeIfStale(cds, rsrc.getChange(), basePs);
+    List<RelatedChangesSorter.PatchSetData> sortedResult =
+        getRelatedUtil.getRelated(changeDataFactory.create(rsrc.getNotes()), basePs);
 
-    for (RelatedChangesSorter.PatchSetData d : sorter.sort(cds, basePs)) {
+    List<RelatedChangeAndCommitInfo> result = new ArrayList<>(sortedResult.size());
+    for (RelatedChangesSorter.PatchSetData d : sortedResult) {
       PatchSet ps = d.patchSet();
       RevCommit commit;
       if (isEdit && ps.id().equals(basePs.id())) {
@@ -134,37 +96,6 @@
     return result;
   }
 
-  @VisibleForTesting
-  public static Set<String> getAllGroups(ChangeNotes notes, PatchSetUtil psUtil) {
-    return psUtil.byChange(notes).stream().flatMap(ps -> ps.groups().stream()).collect(toSet());
-  }
-
-  private List<ChangeData> reloadChangeIfStale(
-      List<ChangeData> changeDatasFromIndex, Change wantedChange, PatchSet wantedPs) {
-    checkArgument(
-        wantedChange.getId().equals(wantedPs.id().changeId()),
-        "change of wantedPs (%s) doesn't match wantedChange (%s)",
-        wantedPs.id().changeId(),
-        wantedChange.getId());
-
-    List<ChangeData> changeDatas = new ArrayList<>(changeDatasFromIndex.size() + 1);
-    changeDatas.addAll(changeDatasFromIndex);
-
-    // Reload the change in case the patch set is absent.
-    changeDatas.stream()
-        .filter(
-            cd -> cd.getId().equals(wantedPs.id().changeId()) && cd.patchSet(wantedPs.id()) == null)
-        .forEach(ChangeData::reloadChange);
-
-    if (changeDatas.stream().noneMatch(cd -> cd.getId().equals(wantedPs.id().changeId()))) {
-      // The change of the wanted patch set is missing in the result from the index.
-      // Load it from NoteDb and add it to the result.
-      changeDatas.add(changeDataFactory.create(wantedChange));
-    }
-
-    return changeDatas;
-  }
-
   static RelatedChangeAndCommitInfo newChangeAndCommit(
       Project.NameKey project, @Nullable Change change, @Nullable PatchSet ps, RevCommit c) {
     RelatedChangeAndCommitInfo info = new RelatedChangeAndCommitInfo();
diff --git a/java/com/google/gerrit/server/restapi/change/GetRelatedUtil.java b/java/com/google/gerrit/server/restapi/change/GetRelatedUtil.java
new file mode 100644
index 0000000..c08e3ed
--- /dev/null
+++ b/java/com/google/gerrit/server/restapi/change/GetRelatedUtil.java
@@ -0,0 +1,119 @@
+// Copyright (C) 2021 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.restapi.change;
+
+import static com.google.common.base.Preconditions.checkArgument;
+import static java.util.stream.Collectors.toSet;
+
+import com.google.common.annotations.VisibleForTesting;
+import com.google.common.flogger.FluentLogger;
+import com.google.gerrit.entities.PatchSet;
+import com.google.gerrit.index.IndexConfig;
+import com.google.gerrit.server.permissions.PermissionBackendException;
+import com.google.gerrit.server.query.change.ChangeData;
+import com.google.gerrit.server.query.change.InternalChangeQuery;
+import com.google.inject.Inject;
+import com.google.inject.Provider;
+import com.google.inject.Singleton;
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.List;
+import java.util.Set;
+
+/** Utility class that gets the ancestor changes and the descendent changes of a specific change. */
+@Singleton
+public class GetRelatedUtil {
+  private static final FluentLogger logger = FluentLogger.forEnclosingClass();
+
+  private final Provider<InternalChangeQuery> queryProvider;
+  private final RelatedChangesSorter sorter;
+  private final IndexConfig indexConfig;
+  private final ChangeData.Factory changeDataFactory;
+
+  @Inject
+  GetRelatedUtil(
+      Provider<InternalChangeQuery> queryProvider,
+      RelatedChangesSorter sorter,
+      IndexConfig indexConfig,
+      ChangeData.Factory changeDataFactory) {
+    this.queryProvider = queryProvider;
+    this.sorter = sorter;
+    this.indexConfig = indexConfig;
+    this.changeDataFactory = changeDataFactory;
+  }
+
+  /**
+   * Gets related changes of a specific change revision.
+   *
+   * @param changeData the change of the inputted revision.
+   * @param basePs the revision that the method checks for related changes.
+   * @return list of related changes, sorted via {@link RelatedChangesSorter}
+   */
+  public List<RelatedChangesSorter.PatchSetData> getRelated(ChangeData changeData, PatchSet basePs)
+      throws IOException, PermissionBackendException {
+    Set<String> groups = getAllGroups(changeData.patchSets());
+    logger.atFine().log("groups = %s", groups);
+    if (groups.isEmpty()) {
+      return Collections.emptyList();
+    }
+
+    List<ChangeData> cds =
+        InternalChangeQuery.byProjectGroups(
+            queryProvider, indexConfig, changeData.project(), groups);
+    if (cds.isEmpty()) {
+      return Collections.emptyList();
+    }
+    if (cds.size() == 1 && cds.get(0).getId().equals(changeData.getId())) {
+      return Collections.emptyList();
+    }
+
+    cds = reloadChangeIfStale(cds, changeData, basePs);
+
+    return sorter.sort(cds, basePs);
+  }
+
+  private List<ChangeData> reloadChangeIfStale(
+      List<ChangeData> changeDatasFromIndex, ChangeData wantedChange, PatchSet wantedPs) {
+    checkArgument(
+        wantedChange.getId().equals(wantedPs.id().changeId()),
+        "change of wantedPs (%s) doesn't match wantedChange (%s)",
+        wantedPs.id().changeId(),
+        wantedChange.getId());
+
+    List<ChangeData> changeDatas = new ArrayList<>(changeDatasFromIndex.size() + 1);
+    changeDatas.addAll(changeDatasFromIndex);
+
+    // Reload the change in case the patch set is absent.
+    changeDatas.stream()
+        .filter(
+            cd -> cd.getId().equals(wantedPs.id().changeId()) && cd.patchSet(wantedPs.id()) == null)
+        .forEach(ChangeData::reloadChange);
+
+    if (changeDatas.stream().noneMatch(cd -> cd.getId().equals(wantedPs.id().changeId()))) {
+      // The change of the wanted patch set is missing in the result from the index.
+      // Load it from NoteDb and add it to the result.
+      changeDatas.add(changeDataFactory.create(wantedChange.change()));
+    }
+
+    return changeDatas;
+  }
+
+  @VisibleForTesting
+  public static Set<String> getAllGroups(Collection<PatchSet> patchSets) {
+    return patchSets.stream().flatMap(ps -> ps.groups().stream()).collect(toSet());
+  }
+}
diff --git a/javatests/com/google/gerrit/acceptance/server/change/GetRelatedIT.java b/javatests/com/google/gerrit/acceptance/server/change/GetRelatedIT.java
index 74dfa04..b605594 100644
--- a/javatests/com/google/gerrit/acceptance/server/change/GetRelatedIT.java
+++ b/javatests/com/google/gerrit/acceptance/server/change/GetRelatedIT.java
@@ -47,7 +47,7 @@
 import com.google.gerrit.index.IndexConfig;
 import com.google.gerrit.server.query.change.ChangeData;
 import com.google.gerrit.server.restapi.change.ChangesCollection;
-import com.google.gerrit.server.restapi.change.GetRelated;
+import com.google.gerrit.server.restapi.change.GetRelatedUtil;
 import com.google.gerrit.server.update.BatchUpdate;
 import com.google.gerrit.server.update.BatchUpdateOp;
 import com.google.gerrit.server.update.ChangeContext;
@@ -573,7 +573,7 @@
 
     ChangeData cd = getChange(last);
     assertThat(cd.patchSets()).hasSize(n);
-    assertThat(GetRelated.getAllGroups(cd.notes(), psUtil)).hasSize(n);
+    assertThat(GetRelatedUtil.getAllGroups(cd.notes().getPatchSets().values())).hasSize(n);
 
     assertRelated(cd.change().currentPatchSetId());
   }