Regular Expression for domain validation
A very simple example:
^[a-zA-Z0-9-]+(\.[a-zA-Z0-9-]+){1,}$
From org.apache.common.validator:
DOMAIN_LABEL_REGEX
\p{Alnum}(?>[\p{Alnum}-]*\p{Alnum})*
TOP_LABEL_REGEX
\p{Alpha}{2,}
DOMAIN_NAME_REGEX
^(?:" + DOMAIN_LABEL_REGEX + "\.)+" + "(" + TOP_LABEL_REGEX + ")$
About \p{Alnum}
, \p{Alpha}
, you can refer to util.regex.Pattern