final String template = """
                {"source":{"index":"__SOURCE_INDEX__","size":__SIZE__},"dest":{"index":"__DEST_INDEX__"}}
                """;
        final FessConfig fessConfig = ComponentUtil.getFessConfig();
        final String source = template //
                .replace("__SOURCE_INDEX__", fromIndex)//
                .replace("__SIZE__", fessConfig.getIndexReindexSize())//
                .replace("__DEST_INDEX__", toIndex);