CAMEL-23835: camel-launcher - set classloader on embedded plugins so TUI ServiceLoader works in fat-jar

[ammachado]

Summary

Running the TUI from the camel-launcher fat-jar (java -jar camel-launcher-*.jar tui, ./camel.sh tui, or podman run camel-launcher tui) fails immediately with:

dev.tamboui.terminal.BackendException: No BackendProvider found on classpath.
Add a backend dependency such as tamboui-jline3-backend or tamboui-panama-backend.
	at dev.tamboui.terminal.BackendFactory.tryProviders(BackendFactory.java:139)
	at dev.tamboui.terminal.BackendFactory.create(BackendFactory.java:91)
	at dev.tamboui.tui.TuiRunner.create(TuiRunner.java:186)
	at org.apache.camel.dsl.jbang.core.commands.tui.TuiBackendHelper.createTuiRunner(TuiBackendHelper.java:36)
	...

The same command works under JBang. This is not a packaging problem: tamboui-jline3-backend and its META-INF/services/dev.tamboui.terminal.BackendProvider SPI entry are correctly bundled under BOOT-INF/lib/.

JIRA: https://issues.apache.org/jira/browse/CAMEL-23835

Root cause

tamboui discovers its terminal backend via ServiceLoader.load(BackendProvider.class), which keys off the thread-context classloader (TCCL). The TUI deliberately installs its plugin classloader as the TCCL before starting (CamelMonitor.java:266-267):

// to make ServiceLoader work with tamboui for downloaded JARs
Thread.currentThread().setContextClassLoader(classLoader);

The launcher registers its bundled plugins in CamelLauncherMain.postAddCommands by instantiating them directly and calling customize(...), but never calling setClassLoader:

new TuiPlugin().customize(commandLine, this);   // classLoader stays null

So TuiPlugin.classLoader (and the CamelMonitor it creates) is null, the TCCL is set to null, and ServiceLoader falls back to the system class loader (AppClassLoader). In a Spring Boot fat-jar that loader cannot see the nested BOOT-INF/lib/*.jar (only LaunchedClassLoader can), so the backend is never found. tamboui's SafeServiceLoader.load(Class) then swallows the resulting ServiceConfigurationError/LinkageError (it passes a null error handler), producing the misleading "No BackendProvider found".

Evidence gathered inside the actual fat-jar:

launcher CL: LaunchedClassLoader
[TCCL=null]     SPI class not visible: ClassNotFoundException: dev.tamboui.terminal.BackendProvider  -> providers=0
[TCCL=launched] providers=1

The embedded-plugin scanning path (PluginHelper.addEmbeddedPlugins) is not involved here: it finds the service resources but their nested URLs (jar:nested:.../fat.jar/!BOOT-INF/lib/...) make new JarFile(...) throw, so it silently registers nothing. The launcher relies entirely on postAddCommands. JBang works because there the TUI plugin is a downloaded plugin loaded through a path that already calls setClassLoader(...).

Fix

CamelLauncherMain.postAddCommands now sets the fat-jar classloader (this class's classloader, i.e. LaunchedClassLoader) on each embedded plugin before customizing it:

ClassLoader classLoader = getClass().getClassLoader();
for (Plugin plugin : List.of(new GeneratePlugin(), new KubernetesPlugin(),
        new TuiPlugin(), new ValidatePlugin(), new TestPlugin())) {
    plugin.setClassLoader(classLoader);
    plugin.customize(commandLine, this);
}

Plugin.setClassLoader is a default no-op, so this is harmless for the other bundled plugins.

Verification

• End-to-end against the rebuilt fat-jar: java -jar camel-launcher-*.jar tui no longer throws BackendException (zero occurrences of "No BackendProvider found"); JLine's terminal provider initializes and the TUI enters raw mode and renders.
• Regression test: CamelLauncherTest#testEmbeddedTuiPluginReceivesClassLoader drives postAddCommands and asserts the registered TUI monitor command received a non-null classloader that can load dev.tamboui.terminal.BackendProvider. Verified it fails without the fix (expected: not <null>) and passes with it. Full CamelLauncherTest green.

Notes

• The misleading error message originates upstream in tamboui (SafeServiceLoader.load(Class) discards the real LinkageError/ServiceConfigurationError). Worth reporting to tamboui separately; out of scope here.
• No upgrade-guide entry: pure bug fix with nothing to migrate.

Claude Code on behalf of Adriano Machado

🤖 Generated with Claude Code

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🧪 CI tested the following changed modules:

• dsl/camel-jbang/camel-launcher

💡 Manual integration tests recommended:

You modified dsl/camel-jbang/camel-launcher. The related integration tests in dsl/camel-jbang/camel-jbang-it are excluded from CI. Consider running them manually:

mvn verify -f dsl/camel-jbang/camel-jbang-it -Djbang-it-test

All tested modules (2 modules)

• Camel :: Launcher
• Camel :: Launcher :: Container

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[davsclaus]

LGTM — clean fix for the TUI "No BackendProvider found" failure in the fat-jar. Setting the classloader on all embedded plugins in postAddCommands is the right approach, and the regression test verifies the wiring end-to-end.

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