CAMEL-24526: camel-djl - reject the zoo tabular applications instead of returning no-op predictors

[oscerd]

Issue

CAMEL-24526

Problem

ZooLinearRegressionPredictor and ZooSoftmaxRegressionPredictor were empty stubs:

@Override
public void process(Exchange exchange) throws Exception {
    // TODO: impl
}

ModelPredictorProducer.getZooPredictor() routes djl:tabular/linear_regression and
djl:tabular/softmax_regression (in zoo mode) to these classes, so the producer did nothing and
the exchange body was passed through unchanged — the input was silently returned as if it were the
model's prediction. This is a silent wrong-result bug: a route appears to run a regression but never
does.

Why not just implement them?

The DJL model zoo publishes no tabular regression models — the test class documents exactly this
(ModelPredictorProducerTest lines 92–93: "No builtin zoo model available for tabular/linear_regression / softmax_regression"),
consistent with the other applications that have no downloadable artifact. Unlike CV (Image →
Classifications) or NLP (String → …), a tabular model has no fixed input/output type pair and DJL
provides no generic tabular Translator; those types are specific to the user's data. There is
therefore nothing generic a zoo predictor could load or translate. The supported way to run a tabular
model is the custom variant (CustomTabularPredictor), where the user supplies their own Model
and Translator via the registry.

Fix

• Remove the two no-op stub classes.
• getZooPredictor() now throws a clear RuntimeCamelException for the tabular applications,
  telling the user to provide their own model and translator and use the custom predictor instead —
  a loud, actionable failure instead of a silently wrong result.
• Add testGetZooPredictorRejectsTabularApplications covering both applications.

The custom tabular path (CustomTabularPredictor) is unchanged and still fully supported.

Testing

• mvn -pl components/camel-ai/camel-djl test (new test green; existing tests unaffected).
• mvn -Psourcecheck validate green (formatter + impsort).

Claude Code on behalf of oscerd

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🧪 CI tested the following changed modules:

• components/camel-ai/camel-djl

---

🔬 Scalpel shadow comparison — Scalpel: 9 tested, 28 compile-only — current: 9 all tested

Maveniverse Scalpel detected 37 affected modules (current approach: 9).

⚠️ Modules only in Scalpel (28)

• apache-camel
• camel-allcomponents
• camel-catalog
• camel-catalog-console
• camel-catalog-maven
• camel-catalog-suggest
• camel-componentdsl
• camel-csimple-maven-plugin
• camel-endpointdsl
• camel-endpointdsl-support
• camel-itest
• camel-jbang-core
• camel-jbang-it
• camel-jbang-main
• camel-jbang-plugin-edit
• camel-jbang-plugin-generate
• camel-jbang-plugin-kubernetes
• camel-jbang-plugin-test
• camel-kamelet-main
• camel-launcher
• camel-report-maven-plugin
• camel-route-parser
• camel-yaml-dsl
• camel-yaml-dsl-deserializers
• camel-yaml-dsl-maven-plugin
• coverage
• docs
• dummy-component

Skip-tests mode would test 9 modules (1 direct + 8 downstream), skip tests for 28 (generated code, meta-modules)

Modules Scalpel would test (9)

• camel-djl
• camel-jbang-mcp
• camel-jbang-plugin-mcp
• camel-jbang-plugin-route-parser
• camel-jbang-plugin-tui
• camel-jbang-plugin-validate
• camel-launcher-container
• camel-yaml-dsl-validator
• camel-yaml-dsl-validator-maven-plugin

Modules with tests skipped (28)

• apache-camel
• camel-allcomponents
• camel-catalog
• camel-catalog-console
• camel-catalog-maven
• camel-catalog-suggest
• camel-componentdsl
• camel-csimple-maven-plugin
• camel-endpointdsl
• camel-endpointdsl-support
• camel-itest
• camel-jbang-core
• camel-jbang-it
• camel-jbang-main
• camel-jbang-plugin-edit
• camel-jbang-plugin-generate
• camel-jbang-plugin-kubernetes
• camel-jbang-plugin-test
• camel-kamelet-main
• camel-launcher
• camel-report-maven-plugin
• camel-route-parser
• camel-yaml-dsl
• camel-yaml-dsl-deserializers
• camel-yaml-dsl-maven-plugin
• coverage
• docs
• dummy-component

ℹ️ Shadow mode — Scalpel observes but does not affect test execution. Learn more

⚠️ Some tests are disabled on GitHub Actions (@DisabledIfSystemProperty(named = "ci.env.name")) and require manual verification:

• components/camel-ai/camel-djl: 1 test(s) disabled on GitHub Actions

All tested modules (37 modules)

• Camel :: AI :: Deep Java Library
• Camel :: All Components Sync point
• Camel :: Assembly
• Camel :: Catalog :: CSimple Maven Plugin (deprecated)
• Camel :: Catalog :: Camel Catalog
• Camel :: Catalog :: Camel Report Maven Plugin
• Camel :: Catalog :: Camel Route Parser
• Camel :: Catalog :: Console
• Camel :: Catalog :: Dummy Component
• Camel :: Catalog :: Maven
• Camel :: Catalog :: Suggest
• Camel :: Component DSL
• Camel :: Coverage
• Camel :: Docs
• Camel :: Endpoint DSL
• Camel :: Endpoint DSL :: Support
• Camel :: Integration Tests
• Camel :: JBang :: Core
• Camel :: JBang :: Integration tests
• Camel :: JBang :: MCP
• Camel :: JBang :: Main
• Camel :: JBang :: Plugin :: Edit
• Camel :: JBang :: Plugin :: Generate
• Camel :: JBang :: Plugin :: Kubernetes
• Camel :: JBang :: Plugin :: MCP
• Camel :: JBang :: Plugin :: Route Parser
• Camel :: JBang :: Plugin :: TUI
• Camel :: JBang :: Plugin :: Testing
• Camel :: JBang :: Plugin :: Validate
• Camel :: Kamelet Main
• Camel :: Launcher
• Camel :: Launcher :: Container
• Camel :: YAML DSL
• Camel :: YAML DSL :: Deserializers
• Camel :: YAML DSL :: Maven Plugins
• Camel :: YAML DSL :: Validator
• Camel :: YAML DSL :: Validator Maven Plugin

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⚙️ View full build and test results

[gnodet]

Nice fix — the deleted ZooLinearRegressionPredictor and ZooSoftmaxRegressionPredictor were genuine stubs with empty process() methods (// TODO: impl), so replacing them with a clear RuntimeCamelException is the right approach. The error message is actionable, directing users to the custom predictor path which remains fully functional.

One thing I believe is missing:

Upgrade guide entry — This PR changes user-visible behavior: routes using djl:tabular/linear_regression or djl:tabular/softmax_regression in zoo mode previously completed silently (no-op); they now throw a RuntimeCamelException. Per project convention, this should be documented in camel-4x-upgrade-guide-4_23.adoc.

There is direct precedent: CAMEL-22518 (commit 66d00a5f6ab) removed the nlp/word_embedding zoo path under identical circumstances and included an upgrade guide entry in camel-4x-upgrade-guide-4_21.adoc.

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AI-generated review on behalf of Guillaume Nodet — verify any suggestions before applying.