code: private static void forceClearCompilerCache() {
          if (CLEAR_COMPILER_CACHE != null && SHARED_ZIP_FILE_INDEX_CACHE != null) {
              try {
                  CLEAR_COMPILER_CACHE.invoke(SHARED_ZIP_FILE_INDEX_CACHE);
              } catch (IllegalAccessException | InvocationTargetException e) {
                  LOG.warn("Failed to force-clear compiler caches, even though it should have been possible." +
                          "This will probably leak memory", e);
              }
          }
      }
docs: clear a shared "zip file index" cache, when it is close()'d. We try to clear it by force.