public static String normalize(String content, short ws) {
        int len = content == null ? 0 : content.length();
        if (len == 0 || ws == WS_PRESERVE)
            return content;

        StringBuffer sb = new StringBuffer();
        if (ws == WS_REPLACE) {
            char ch;
            // when it's replace, just replace #x9, #xa, #xd by #x20
            for (int i = 0; i < len; i++) {
                ch = content.charAt(i);
                if (ch != 0x9 && ch != 0xa && ch != 0xd)
                    sb.append(ch);
                else
                    sb.append((char)0x20);
            }
        } else {
            char ch;
            int i;
            boolean isLeading = true;
            // when it's collapse
            for (i = 0; i < len; i++) {
                ch = content.charAt(i);
                // append real characters, so we passed leading ws
                if (ch != 0x9 && ch != 0xa && ch != 0xd && ch != 0x20) {
                    sb.append(ch);
                    isLeading = false;
                }
                else {
                    // for whitespaces, we skip all following ws
                    for (; i < len-1; i++) {
                        ch = content.charAt(i+1);
                        if (ch != 0x9 && ch != 0xa && ch != 0xd && ch != 0x20)
                            break;
                    }
                    // if it's not a leading or tailing ws, then append a space
                    if (i < len - 1 && !isLeading)
                        sb.append((char)0x20);
                }
            }
        }

        return sb.toString();
    }