I have not found a regexp to do this. I need to validate the "Message-ID:" value from an email. It is similar to a email address validation regexp but much simpler, without most of the edge cases the email address allows, from rfc2822
msg-id = [CFWS] "<" id-left "@" id-right ">" [CFWS]
id-left = dot-atom-text / no-fold-quote / obs-id-left
id-right = dot-atom-text / no-fold-literal / obs-id-right
no-fold-quote = DQUOTE *(qtext / quoted-pair) DQUOTE
no-fold-literal = "[" *(dtext / quoted-pair) "]"
Let's say the outter <> are optional. dot-atom-text and missing definitions can be found in rfc2822
I am not proficient in regex and I prefer to use an already tested one, if exists.
As I could not find any I ended up implementing it myself. It is not a proper validation as per RFC2822 but a good enough aproximation for now:
static String VALIDMIDPATTERN = "[a-z0-9!#$%&'*+/=?^_`{|}~-]+(?:\\.[a-z0-9!#$%&'*+/=?^_`{|}~-]+)*@[a-z0-9!#$%&'*+/=?^_`{|}~-]+(?:\\.[a-z0-9!#$%&'*+/=?^_`{|}~-]+)*";
private static Pattern patvalidmid = Pattern.compile(VALIDMIDPATTERN);
public static boolean isMessageIdValid(String midt) {
String mid = midt;
if (StringUtils.countMatches(mid, "<") > 1)
return false;
if (StringUtils.countMatches(mid, ">") > 1)
return false;
if (StringUtils.containsAny(mid, "<>")) {
mid = StringUtils.substringBetween(mid, "<", ">");
if (StringUtils.isBlank(mid)) {
return false;
}
}
if (StringUtils.contains(mid, "..")) {
return false;
}
//extract from <>
mid = mid.trim();
//now validate
Matcher m = patvalidmid.matcher(mid);
return m.matches();
}