ammachado opened a new pull request, #24258:
URL: https://github.com/apache/camel/pull/24258
## Summary
Running the TUI from the `camel-launcher` fat-jar (`./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 when the CLI is installed via 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 own
classloader as the TCCL before starting (`CamelMonitor.java:266-267`):
```java
// to make ServiceLoader work with tamboui for downloaded JARs
Thread.currentThread().setContextClassLoader(classLoader);
```
That `classLoader` arrives as `null` for **embedded** (fat-jar) plugins,
because `PluginHelper.loadPluginFromService(...)` instantiates the plugin and
calls `customize(...)` but, unlike the two downloaded-plugin paths
(`PluginHelper.java:344` and `:520`, which both call
`instance.setClassLoader(...)`), never calls `setClassLoader`. So
`TuiPlugin.classLoader` stays `null` → `CamelMonitor.classLoader` is `null` →
the TCCL is set to `null`.
With a `null` TCCL, `ServiceLoader` falls back to the system class loader
(`AppClassLoader`), which cannot see the nested `BOOT-INF/lib/*.jar` of a
Spring Boot fat-jar (only `LaunchedClassLoader` can). The provider is never
found, and TamboUI's `SafeServiceLoader.load(Class)` silently swallows the
resulting `ServiceConfigurationError`/`LinkageError` (it passes a `null` error
handler), producing the misleading "No BackendProvider found".
Proven directly inside the actual fat-jar:
```
probe loaded by: LaunchedClassLoader
system CL: AppClassLoader
[TCCL=null] SPI class not visible: ClassNotFoundException:
dev.tamboui.terminal.BackendProvider -> providers=-1
[TCCL=launched] providers=1
```
JBang works because there the TUI plugin is a *downloaded* plugin, which
goes through a path that calls `setClassLoader(...)` with a non-null
classloader chaining to the TamboUI jars.
## Fix
In `PluginHelper.loadPluginFromService(...)`, hand the loading classloader
to the plugin before customizing it, mirroring the downloaded-plugin paths:
```java
Plugin plugin = (Plugin) pluginClass.getDeclaredConstructor().newInstance();
plugin.setClassLoader(classLoader); // added
```
`Plugin.setClassLoader` is a `default` no-op, so this is harmless for every
other bundled plugin.
## Tests
Added `PluginHelperTest#testEmbeddedPluginReceivesClassLoader`, which drives
`loadPluginFromService` with a capturing `Plugin` and asserts it receives the
exact classloader used to load it. Verified it fails without the fix
(`expected: <1> but was: <0>`) and passes with it. Full `PluginHelperTest` (10
tests) 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](https://claude.com/claude-code)
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