Validator for email addresses, host names, IP addresses

[willhains]

Email address validation can be tricky.
Should there be an explicit validator rule for email address strings?
There may also be some performance benefit to validate by code rather than by regex.

Proposed API

@EmailAddress
public final @Value class EmailAddress extends PureString<EmailAddress> {...}

@HostName
public final @Value class HostName extends PureString<HostName> {...}

@IPAddress
public final @Value class ServerIP extends PureString<ServerIP> {...}

Alternatives

Rather than creating separate annotations for each, provide constants for special cases:

@Matching(EMAIL_ADDRESS)
public final @Value class EmailAddress extends PureString<EmailAddress> {...}

@Matching(HOST_NAME)
public final @Value class HostName extends PureString<HostName> {...}

@Matching(IP_V4_ADDRESS)
public final @Value class ServerIP extends PureString<ServerIP> {...}

These could be well-tested regex patterns, or special constant string values that the @Matching rule checks for, and invokes non-regex logic for faster validation.