code: public static List<String> getFilesByChange(GerritQueryHandler gerritQueryHandler, String changeId) {
          try {
              List<JSONObject> jsonList = gerritQueryHandler.queryFiles("change:" + changeId);
              for (JSONObject json : jsonList) {
                  if (json.has("type") && "stats".equalsIgnoreCase(json.getString("type"))) {
                      continue;
                  }
                  if (json.has("currentPatchSet")) {
                      JSONObject currentPatchSet = json.getJSONObject("currentPatchSet");
                      if (currentPatchSet.has("files")) {
                          JSONArray changedFiles = currentPatchSet.optJSONArray("files");
                          int numberOfFiles = changedFiles.size();
  
                          if (numberOfFiles > 0) {
                              List<String> files = new ArrayList<String>(numberOfFiles);
                              for (int i = 0; i < changedFiles.size(); i++) {
                                  JSONObject file = changedFiles.getJSONObject(i);
                                  files.add(file.getString("file"));
                              }
                              return files;
                          }
                      }
  
                      break;
                  }
              }
          } catch (IOException e) {
              logger.error("IOException occurred. ", e);
          } catch (GerritQueryException e) {
              logger.error("Bad query. ", e);
          }
          return null;
      }
docs: Provides list of files related to the change.
  @param gerritQueryHandler the query handler, responsible for the queries to gerrit.
  @param changeId the Gerrit change id.
  @return list of files from the change, null in case of errors