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Trailing Slash Behavior Change in FME Flow REST API V4

Tandra Geraedts
Tandra Geraedts
  • Updated

Considerations

As of FME Flow 2026.1, the FME Flow REST API framework has been updated, which may cause REST API calls to return a 404 error if the URL ends with a trailing slash (e.g., /flow/api/example/). This change only affects the FME Flow REST API V4 endpoints, not other APIs you may be using with FME.

Why This Happens

As part of upgrading to Spring Framework 6 (via Spring Boot 3), the URL-matching behavior has changed: if a URL has a trailing slash, it will no longer be automatically matched to a URL without a trailing slash.

Under Spring Framework 5 (previous behavior):

  • /flow/api/example/ matched the endpoint
  • /flow/api/example matched the endpoint

Under Spring Framework 6 (new behavior):

  • /flow/api/example/ does not match
  • /flow/api/example matches

Trailing slashes are no longer automatically normalized. The framework now treats these as two distinct URLs, and only the exact configured path is valid. This change is documented in the official Spring migration guide.

Because FME Flow 2026.1 and newer use this updated framework, the behavior change applies to REST API V4.

How to Resolve It

To ensure your API calls continue working:

1. Review all scripts, integrations, and applications that call FME Flow REST API V4.

2. Remove any trailing slashes from endpoint URLs.

3. Confirm that requests use the exact endpoint path as documented.

Example:

Instead of:

https://<your-fme-flow-host>/flow/api/example/

Use:

https://<your-fme-flow-host>/flow/api/example

This may require updates to:

  • Automation scripts
  • Python or JavaScript integrations
  • Scheduled jobs
  • Third-party tools that call the API

After updating the URLs, test each integration to confirm successful responses.

Additional Notes

  • This change does not affect earlier versions of FME Flow, only 2026.1 and newer
  • This change does not affect REST API V3
  • The behavior is by design due to the underlying framework upgrade

Additional Resources

Spring Boot 3.0 Migration Guide – URL Matching Changes
https://github.com/spring-projects/spring-boot/wiki/Spring-Boot-3.0-Migration-Guide#spring-mvc-and-webflux-url-matching-changes.

If you continue experiencing unexpected 404 errors after upgrading, contact Safe Software Support

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