FINERACT-2511: Validate dateFormat parameter to return HTTP 400 instead of 500

[Harshitmehra-270709]

Description

Fixes FINERACT-2511: Invalid dateFormat on client create returns HTTP 500 instead of 400 Bad Request.

Root Cause

When an invalid dateFormat value (e.g., 02 February 2026 instead of a valid pattern like dd MMMM yyyy) is provided in POST /fineract-provider/api/v1/clients, ClientDataValidator.validateForCreate() does not validate this parameter. The invalid value reaches DateTimeFormatter.ofPattern(command.dateFormat()) in ClientWritePlatformServiceJpaRepositoryImpl.createClient(), which throws IllegalArgumentException. This uncaught exception surfaces as HTTP 500.

Changes

1. DataValidatorBuilder.java - Added a reusable validDateTimeFormatPattern() method that validates date/time format pattern strings by attempting DateTimeFormatter.ofPattern() and catching IllegalArgumentException. This method follows the existing fluent API pattern and can be reused by other validators across the codebase.

2. ClientDataValidator.java - Added dateFormat validation in both validateForCreate() and validateForUpdate() using the new validDateTimeFormatPattern() method. Invalid patterns are now caught during validation and returned as HTTP 400 with a clear error message.

3. DataValidatorBuilderDateFormatTest.java [NEW] - 12 parameterized unit tests covering:

   • Valid patterns (dd MMMM yyyy, yyyy-MM-dd, dd/MM/yyyy, MM/dd/yyyy, dd-MM-yyyy HH:mm:ss)
   • Invalid patterns (02 February 2026, not-a-pattern, P!@#$, {{invalid}})
   • Null value handling (with and without ignoreIfNull)
   • Blank value handling

Testing

• All 12 unit tests pass (0 failures, 0 errors)
• fineract-core:compileJava BUILD SUCCESSFUL
• Code formatted via spotlessJavaApply

[adamsaghy]

@Harshitmehra-270709 Please rebase this PR with latest develop branch.
Please make sure you have a configured GPG signature and valid email address.

[Harshitmehra-270709]

@Harshitmehra-270709 Please rebase this PR with latest develop branch. Please make sure you have a configured GPG signature and valid email address.

Yes, sir, I did all the changes, and I have a question: Where do all the contributors and maintainers hang out?
or discuss things?

[adamsaghy]

@Harshitmehra-270709 Please rebase this PR with latest develop branch. Please make sure you have a configured GPG signature and valid email address.

Yes, sir, I did all the changes, and I have a question: Where do all the contributors and maintainers hang out? or discuss things?

Official dev mail list:
https://fineract.apache.org -> Mailing list

Unofficial slack channel:
"Mifos" as the organization and look for "fineract" channel.