public static StringBuilder epochMillis(long timeMillis) {
        // 24 (human readable part) + 2 (parens) + 19 (max digits of a long integer)
        final StringBuilder buf = new StringBuilder(45);
        appendEpochMillis(buf, timeMillis);
        return buf;
    }
Formats the given epoch time in milliseconds to typical human-readable format
"yyyy-MM-dd'T'HH:mm:ss.SSSX".

@param timeMillis epoch time in milliseconds

@return the human readable string representation of the given epoch time
core/src/main/java/com/linecorp/armeria/common/util/TextFormatter.java