jamesfredley opened a new pull request, #15411:
URL: https://github.com/apache/grails-core/pull/15411
## Summary
Fixes two Micronaut integration bugs by automating configuration that
previously required manual `build.gradle` setup:
- **#15207** - `java -jar` broken for grails-micronaut apps due to Spring
Boot 3.2+ default loader incompatibility
- **#15211** - Java `@Singleton` beans not registered when using Groovy
incremental compilation (missing annotation processor)
## Problem
### Issue #15207 - `java -jar` fails with `NoClassDefFoundError`
Spring Boot 3.2+ changed the default `LoaderImplementation` from `CLASSIC`
to a new implementation. The new loader is incompatible with Micronaut-Spring's
classpath scanning mechanism (`MicronautImportRegistrar`), causing
`NoClassDefFoundError` at runtime when running a packaged JAR/WAR via `java
-jar`.
### Issue #15211 - Java `@Singleton` beans silently ignored
Groovy sources use `micronaut-inject-groovy` AST transforms to generate
`BeanDefinitionReference` classes. However, Java sources in a Grails project
require the `micronaut-inject-java` annotation processor on the
`annotationProcessor` configuration. Without it, Java beans annotated with
`@Singleton`, `@Factory`, etc. are silently ignored - no compile error, just
missing beans at runtime.
## Solution
### GrailsGradlePlugin (`configureMicronaut()`)
1. **Annotation processor** - Automatically adds `micronaut-inject-java` +
`jakarta.annotation-api` to the `annotationProcessor` configuration, scoped to
the Micronaut platform BOM. This only affects `compileJava` tasks (Groovy
sources continue using AST transforms via `compileOnlyApi`).
2. **CLASSIC loader** - Configures `bootJar` and `bootWar` tasks with
`LoaderImplementation.CLASSIC` as a convention default (overridable by users).
This ensures `java -jar` works correctly with Micronaut-Spring's classpath
scanning.
### Forge Template
Adds the missing `bootWar` CLASSIC loader configuration to match the
existing `bootJar` configuration in Forge-generated `build.gradle` files.
### Housekeeping
- Adds Apache license header to `GrailsMicronautValidator.java`
- Replaces `// TODO:` with `// See:` to satisfy Forge checkstyle
`TodoComment` rule
## Commits
| Commit | Description |
|--------|-------------|
| `fix: configure Micronaut annotation processor and CLASSIC loader in
GrailsGradlePlugin` | Core fix - adds annotation processor for Java sources +
CLASSIC loader convention for bootJar/bootWar |
| `fix: add bootWar CLASSIC loader to Forge-generated build.gradle` | Forge
template parity - bootWar was missing CLASSIC loader config |
| `chore: add Apache license header to GrailsMicronautValidator` | License
header + checkstyle compliance |
| `test: add integration tests for Micronaut bean type registration` | New
`MicronautBeanTypesSpec` covering Java @Singleton, Groovy @Factory/@Bean, and
@ConfigurationProperties bean registration |
| `docs: document Micronaut annotation processor and CLASSIC loader in
upgrade guide` | Upgrade guide notes warning against manual annotation
processor setup |
## Test Coverage
**21 integration tests passing** in `grails-test-examples-micronaut`:
- `BeanInjectionServiceSpec` (3 tests) - existing Micronaut bean injection
tests
- `MicronautBeanTypesSpec` (5 tests) - **NEW** - Java @Singleton,
@Factory/@Bean, @ConfigurationProperties, singleton identity checks
- `MicronautContextSpec` (6 tests) - existing context bridge tests
- `MicronautQualifierSpec` (7 tests) - existing qualifier/named bean tests
### New test bean types added:
| Bean | Type | Registration Path |
|------|------|-------------------|
| `JavaSingletonService` | Java class | `@Singleton` via annotation
processor |
| `FactoryCreatedService` | Groovy POJO | `@Factory`/`@Bean` via AST
transform |
| `ServiceFactory` | Groovy factory | `@Factory` with `@Singleton` method |
| `AppConfig` | Groovy config | `@ConfigurationProperties('app')` bound from
`application.yml` |
## Build Verification
| Project | Status |
|---------|--------|
| `grails-gradle` (plugins) | :white_check_mark: BUILD SUCCESSFUL |
| `grails-forge` (checkstyle) | :white_check_mark: BUILD SUCCESSFUL |
| `grails-doc` (guide) | :white_check_mark: BUILD SUCCESSFUL |
| `codeStyle` (main project) | :white_check_mark: BUILD SUCCESSFUL |
| `grails-test-examples-micronaut:integrationTest` | :white_check_mark:
21/21 PASSED |
## Remaining Gaps (Out of Scope)
These are known limitations of the current Micronaut integration, not
addressed by this PR:
- `spring-boot-devtools` incompatibility
([micronaut-spring#769](https://github.com/micronaut-projects/micronaut-spring/issues/769))
- Groovy incremental compilation may re-trigger AST transforms on unchanged
files (Groovy compiler limitation)
- No `bootRun` CLASSIC loader needed (only affects packaged archives)
Fixes #15207
Fixes #15211
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