NIFI-15674: Add isValidDate and isValidInstant Expression Language fu…

[Scrooge-McDucks]

Summary

NIFI-15674

Adds two new Expression Language validation functions:

• isValidDate(format[, timezone])
• isValidInstant()

These functions allow flows to validate date and instant values before attempting conversion.

Motivation

NiFi currently does not provide a simple top-level Expression Language function for validating whether a value can be parsed as a date or instant.

Today, users often need to rely on regex, nested expressions, or extra processor logic in places like UpdateAttribute or RouteOnAttribute to guard parsing. Regex can validate shape, but it is not calendar-aware, so values like 31-02-2026 may still appear valid even though they are not real dates.

This also creates operational risk. If invalid values are parsed directly, expression evaluation can fail, which in some flows can lead to repeated retries or queue looping instead of clean handling.

These functions provide a lightweight and safe way to keep validation logic visible at the top level of an expression.

Behavior

isValidDate(format)

Returns true if the subject can be parsed as a valid date using the supplied format, otherwise false.

isValidDate(format, timezone)

Returns true if the subject can be parsed as a valid date using the supplied format and timezone, otherwise false.

isValidInstant()

Returns true if the subject can be parsed as a valid ISO-8601 instant, otherwise false.

Invalid input returns false rather than throwing an evaluation error.

Examples

${myDate:isValidDate("dd-MM-yyyy"):ifElse("valid","invalid")}

${myDate:isValidDate("yyyy-MM-dd HH:mm:ss", "UTC")}

${eventTime:isValidInstant():ifElse("valid-instant","invalid-instant")}

Tracking

Please complete the following tracking steps prior to pull request creation.

Issue Tracking

• Apache NiFi Jira issue created

Pull Request Tracking

• Pull Request title starts with Apache NiFi Jira issue number, such as NIFI-00000
• Pull Request commit message starts with Apache NiFi Jira issue number, as such NIFI-00000
• Pull request contains commits signed with a registered key indicating Verified status

Pull Request Formatting

• Pull Request based on current revision of the main branch
• Pull Request refers to a feature branch with one commit containing changes

Verification

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Build

• Build completed using ./mvnw clean install -P contrib-check
  • JDK 21
  • JDK 25

Licensing

• New dependencies are compatible with the Apache License 2.0 according to the License Policy
• New dependencies are documented in applicable LICENSE and NOTICE files

Documentation

• Documentation formatting appears as expected in rendered files