PoC: Built-in OpenAPI routing with controller.json

[joewiz]

Summary

Add built-in OpenAPI routing to eXist-db via controller.json + api.json. Apps define REST endpoints declaratively in an OpenAPI 3.0 spec; eXist automatically routes requests to XQuery handler functions by operationId. This eliminates the need for Roaster and the controller.xql + api.xq + $lookup boilerplate.

What Changed

All new code is in the exist-services Maven module (not exist-core), per the architectural principle that exist-core should contain only the core database engine.

New classes in exist-services/

• OpenApiServiceRegistry.java — in-memory routing table with path pattern matching
• OpenApiServlet.java — dispatches matched routes to XQuery handlers
• OpenApiStartupTrigger.java — scans /db/apps/ at startup for controller.json
• OpenApiTrigger.java — collection trigger for auto-discovery on storage events

Configuration

• web.xml — OpenApiServlet registration
• controller-config.xml — URL pattern forwarding for /openapi/
• conf.xml — startup trigger registration

Demo app

• exist-core/src/test/resources/openapi-demo/ — three endpoints, no Roaster, no controller.xql

Architecture

controller.json (in app collection)
    └── references api.json (OpenAPI 3.0 spec)
            └── operationId: "prefix:functionName"
                    └── OpenApiServlet resolves to XQuery module + function
                            └── Handler returns map → servlet serializes as JSON

Relationship to PR #6247

This PR builds on #6247 (feature/builtin-package-api). Both share the exist-services module.

Test Plan

• mvn install -pl exist-services -am -DskipTests compiles cleanly
• Dashboard tests pass without Roaster installed
• Apps using controller.json route correctly via OpenApiServlet

🤖 Generated with Claude Code

[adamretter]

May I suggest that this should go into its own module. The exist-core module was created with the specific purpose of being slimmed down rather than made bigger, the previous plans was to remove everything from exist-core apart from core database engine.