The Filter Development Kit is a Java framework that extends Axway API Gateway with capabilities the platform does not provide out of the box: calling policies from scripts, resolving selectors cleanly, sharing code between scripts, exposing Java methods as selectors, creating fully packaged custom filters with a Policy Studio UI, and hot-reloading code changes without a gateway restart.
A Docker-based playground is provided so you can have a working gateway, an IDE, and all FDK features running in a single container within minutes. See Getting Started.
| Pain point | FDK solution |
|---|---|
| Scripts cannot call other policies | Advanced Script Filter / Script Context |
| Scripts cannot resolve selectors properly | Resource binding with type coercion |
| Scripts cannot access KPS or caches with proper references | KPS and Cache resources |
| Code is duplicated across scripts (copy/paste) | Groovy resource reflection + export |
| JUEL's built-in reflection resolver can call Java methods at invocation time, but the message is not part of the JUEL context — it is designed for self-contained objects, with no type coercion and no message access | Extension Context pre-registers functions at configuration time; the message is injected directly from the resolver context, and parameter type coercion is handled automatically — no glue filters needed to convert arguments before the call |
| Custom filters require complex GUI maintenance | Java Quick Filters (generated from annotations) |
| Adding a library causes dependency conflicts | Child-first ClassLoader |
| Testing requires a gateway restart | Dynamic Compiler |
| Feature | What it does | Requires typeset | Standalone |
|---|---|---|---|
| Script Context | Adds resource binding to the standard Groovy script filter | No | — |
| Script Extensions | Adds Java-backed top-level functions to any script | No | — |
| Advanced Script Filter | Enhanced script filter with full resource and reflection API | Yes | — |
| Extension Context | Exposes Java methods as API Gateway selectors | Yes | — |
| Extension Interface | Shares a Java interface between FDK and custom filters | Yes | — |
| Child-first ClassLoader | Isolates conflicting third-party libraries | Yes | — |
| Java Quick Filters | Generates complete Policy Studio filters from annotated Java | No¹ (own typeset) | Yes |
| Dynamic Compiler | Compiles Java on deploy; no restart needed | Yes | — |
¹ Quick Filter archives embed their own typesets and are imported independently, but filter-devkit-runtime must be installed in the gateway ext/lib.
Do you want to create a new filter that appears in the Policy Studio palette?
├─ Yes → Java Quick Filters (docs/QuickFilters.md)
│ Each filter archive is self-contained; no other installation needed.
│
└─ No → Do you want the full feature set (Extension Context global namespace,
Extension Interface, child-first ClassLoader, Advanced Script Filter)?
├─ Yes → Full install: deploy runtime jars + import typeset
│ → docs/BuildAndInstall.md, then docs/Architecture.md (§ Installation modes)
│
└─ No → Script-only install: deploy runtime jars, no typeset import
Gives you: Script Context, Script Extensions
→ docs/GettingStarted.md (§ Manual install)
| Document | Read it when… |
|---|---|
| Getting Started | You want a working example as fast as possible |
| Architecture | You want to understand how the pieces fit together |
| Concepts | You want the mental model before diving into features |
| Scripting Guide | You are enhancing scripts (calling policies, resolving selectors, sharing code) |
| Java Extensions | You are exposing Java methods to selectors or custom filters |
| Java Quick Filters | You are building a new filter with a Policy Studio UI |
| Dynamic Compiler | You want faster iteration without gateway restarts |
| Build & Install | You are setting up the build from source |
| Migration | You are migrating from a legacy FDK release |
| Reference | You need the full annotation and runtime API |
- JDK 11
- API Gateway and Policy Studio 7.7.20260228
- Gradle (wrapper included)
git
The codebase has been tested from version 20220530 (JDK 8) through 20260228 (JDK 11). Always use artifacts built for the API Gateway version you are targeting — bytecode differences between releases can trigger MethodNotFoundException. If no matching branch exists, open an issue or submit a pull request.
Note: The FDK runtime contains no code specific to either Entity Store variant (one log directive in
AbstractScriptProcessoraside), so YAML should work at runtime — it has simply not been tested. Typeset generation targets the XML Entity Store tooling; YAML tooling support is not currently planned.
| Plugin | Description | Typeset required |
|---|---|---|
| Extended Eval Selector | Selector evaluation with native CircuitAbortException propagation | Yes (own typeset) |
| OAuth 2.0 extended Token service | Token exchange, assertion and client_assertion grant support | Yes (own typeset) |
| OAuth 2.0 extended Authorize service | Built-in PKCE support | Yes (own typeset) |
| HTTP Signature | Generation and validation per draft-cavage-http-signatures-12 | Yes (own typeset) |
| JAXRS support | JAX-RS web service behaviour in Groovy scripts | No (extension loading) |
| Circuit Loop | Controlled iteration within policy execution | Yes (own typeset) |
| Script Extensions | Built-in script extension module | No (extension loading) |
| Certificate Manager | Certificate manipulation and JWKS export (work in progress) | No (extension loading) |
| Area | Limitation | Status |
|---|---|---|
| Docker playground | No gateway configuration is provided out of the box. The user must create an XML configuration and import typesets manually before policies can run. Automation of this step is under investigation. | In progress |
| Entity Store | The FDK runtime contains no code specific to either Entity Store variant (one log directive in AbstractScriptProcessor aside), so YAML should work at runtime — it has simply not been tested. Typeset generation targets the XML Entity Store tooling; YAML tooling support is not currently planned. | Not planned |
| Quick Filter UI | No sub-dialogs in generated filter UIs. Complex multi-panel configurations requiring sub-dialogs (such as the Resources tab) cannot be expressed with the current xmlui code generator. | Not planned |
| Certificate Manager plugin | Certificate manipulation and JWKS export for OpenID/OAuth services. | In progress |