walkthrough documentation

showcase-quarkus-eventsourcing/README.md

@@ -63,7 +63,6 @@ $GRAALVM_HOME/bin/java -agentlib:native-image-agent=trace-output=native-image/tr
 
 As described in [Using GraalVM native-image-agent][UsingNativeImageAgent] it is very helpful to use integration tests and run them [against the running application][QuarkusIntegrationTestsAgainstRunningApplication], that was started by one of the commands above with the native image agent activated. This is much easier than clicking through the application manually. 
 
-
 ## Features
 * MicroProfile Standard
 * "Reactive" example using server sent events (tested with safari & chrome browser) and axon subscription query
@@ -76,12 +75,41 @@ As described in [Using GraalVM native-image-agent][UsingNativeImageAgent] it is
 * Full-Stack Build configuration including JavaScript Unit Tests with Jasmine, JavaScript minify, ... 
 * Continuous Integration using [GitHub Actions][GitHubActions] for a fully automated build including Java and JavaScript Unit Tests, Web Packaging, native image and integration-tests.
 
-## Notes
+### Notes
 * Code comments containing the marker ```Note:``` describes thoughts, background information, documented decisions and hints to problems. 
 * ```ArchitectureRulesTest``` defines rules to assure low coupling between the business core, axon and microprofile features.
 * These rules might seem a bit extreme. Some may even find them to be impractical. After all, this examples shows that it can be done.
 * This is just a simple show case, not an full application. 
 
+## Walkthrough
+
+### Connecting Context and Dependency Injection (CDI) to AxonFramework
+
+[Axon Framework CDI Support][AxonFrameworkCDI] already provides a CDI integration by providing a [CDI Portable Extension][CDIExtension].
+Unfortunately, this doesn't work for Quarkus, since [Quarkus CDI][QuarkusCDI]
+only implements a subset of the CDI specification and doesn't support [CDI Portable Extensions][CDIExtension].
+
+#### Bean Discovery
+
+To most important part is the discovery of all building blocks (beans) of AxonFramework. This includes for example finding all aggregates, event handlers, command handlers, query handlers, ...
+
+This is done inside [AxonComponentDiscovery.java](./src/main/java/io/github/joht/showcase/quarkuseventsourcing/messaging/infrastructure/axon/inject/cdi/AxonComponentDiscovery.java), whereas the most important line is probably the following:
+
+```java
+Set<Bean<?>> beans = beanManager.getBeans(Object.class, AnnotationLiteralAny.ANY);
+```
+
+This line seems to work for pretty any CDI implementation including [Quarkus CDI][QuarkusCDI]
+and returns all beans (of any type) that CDI can discover (in respect of its configuration). 
+
+#### Axon Configuration
+
+[AxonConfiguration.java](./src/main/java/io/github/joht/showcase/quarkuseventsourcing/messaging/infrastructure/axon/AxonConfiguration.java) takes all discovered beans and registers them accordingly. It also wires up custom settings (e.g. database schema) and global settings (e.g. bean validation). 
+
+#### Thoughts about application startup
+
+Axon configuration is all done the first time it is used. The disadvantage of it is, that the application might benefit from a warm up. The advantage is, that this can be done strongly within CDI standard. Even if `@Observes @Initialized(ApplicationScope.class)` is standard and could be used to call a method on server start, Quarkus would run this e.g. in native mode during build. For details see [Quarkus Application Initialization and Termination][QuarkusLivecycle].
+
 ## What is [AxonFramework][AxonFramework]?
 
 > Open source framework for event-driven microservices and domain-driven design
@@ -105,20 +133,28 @@ For more details please visit [Quarkus][Quarkus].
 * [ArchUnit][ArchUnit]
 * [Assisted Configuration with Tracing Agent][NativeImageAssistedConfiguration]
 * [AxonFramework][AxonFramework]
+* [Axon Framework CDI Support][AxonFrameworkCDI]
 * [Building a native executable][QuarkusNativeExecutable]
+* [CDI Portable Extension][CDIExtension]
+* [CDI - Jakarta Contexts and Dependency Injection][CDI]
 * [Eclipse MicroProfile][MicroProfile]
 * [EqualsVerifier][EqualsVerifier]
 * [Flyway Version control for your database][Flyway]
 * [GitHub Actions][GitHubActions]
 * [GraalVM][GraalVM]
 * [Jakarta JSON Binding][JSONBinding]
 * [Quarkus][Quarkus]
+* [Quarkus Context and Dependency Injection (CDI)][QuarkusCDI]
 * [Quarkus Integrationtest - Executing against a running application][QuarkusIntegrationTestsAgainstRunningApplication]
+* [Quarkus Application Initialization and Termination][QuarkusLivecycle]
 * [Testing all equals and hashCode methods][TestingEqualsHashcode]
 * [Using GraalVM native-image-agent when porting a library to Quarkus][UsingNativeImageAgent]
 
 [ArchUnit]: https://www.archunit.org
 [AxonFramework]: https://axoniq.io/product-overview/axon-framework
+[AxonFrameworkCDI]: https://github.com/AxonFramework/extension-cdi
+[CDI]: https://jakarta.ee/specifications/cdi
+[CDIExtension]: https://docs.jboss.org/weld/reference/latest/en-US/html/extend.html
 [EqualsVerifier]: https://jqno.nl/equalsverifier
 [Flyway]: https://flywaydb.org
 [GitHubActions]: https://docs.github.com/en/actions
@@ -127,7 +163,9 @@ For more details please visit [Quarkus][Quarkus].
 [MicroProfile]: https://projects.eclipse.org/projects/technology.microprofile
 [NativeImageAssistedConfiguration]: https://www.graalvm.org/reference-manual/native-image/Agent
 [Quarkus]: https://quarkus.io
+[QuarkusCDI]: https://quarkus.io/guides/cdi-reference
 [QuarkusNativeExecutable]: https://quarkus.io/guides/building-native-image-guide
 [QuarkusIntegrationTestsAgainstRunningApplication]: https://quarkus.io/guides/getting-started-testing#executing-against-a-running-application
+[QuarkusLivecycle]: https://quarkus.io/guides/lifecycle
 [TestingEqualsHashcode]: https://joht.github.io/johtizen/testing/2020/03/08/test-all-equal-and-hashcode-methods.html
 [UsingNativeImageAgent]: https://peter.palaga.org/2021/01/31/using-native-image-agent-when-porting-a-lib-to-quarkus.html