Expose more reflection hints (#3951)

* Expose more reflection hints

* Bring back `@Reflective` on `Pausable` - for possible end-user usage
* Add `ReactiveMessageHandler` hint since its method is used reflectively
in the `IntegrationRSocketMessageHandler`
* Add `@Reflective` on the `ServerRSocketMessageHandler.handleConnectionSetup()`
since it is used reflectively for a `registerHandlerMethod()`
* Add `KafkaRuntimeHints` to expose `Pausable` contract on Kafka inbound endpoints
for SpEL invocation via Control Bus
* Document native images support

* Fix language in docs

Co-authored-by: Gary Russell <grussell@vmware.com>

Co-authored-by: Gary Russell <grussell@vmware.com>

src/reference/asciidoc/index-single.adoc

@@ -41,6 +41,8 @@ include::./system-management.adoc[]
 
 include::./reactive-streams.adoc[]
 
+include::./native-aot.adoc[]
+
 include::./endpoint-summary.adoc[]
 
 include::./amqp.adoc[]

src/reference/asciidoc/index.adoc

@@ -28,6 +28,7 @@ Welcome to the Spring Integration reference documentation!
 <<./kotlin-dsl.adoc#kotlin-dsl,Kotlin DSL>> :: Details about Kotlin DSL for EIP
 <<./system-management.adoc#system-management-chapter,System Management>> :: Message store, control bus, integration graph, metrics, JMX
 <<./reactive-streams.adoc#reactive-streams,Reactive Streams Support>> :: Details about Reactive Streams support: message channels, channel adapters etc.
+<<./native-aot.adoc#native-images-support,Native Images Support>> :: GraalVM native images and Spring AOT support
 
 [horizontal]
 **Integration Endpoints** ::

src/reference/asciidoc/native-aot.adoc

@@ -0,0 +1,57 @@
+[[native-images-support]]
+=== Native Images Support
+
+Starting with version 6.0, GraalVM compilation of Spring Integration applications to native images is supported by https://docs.spring.io/spring-framework/docs/current/reference/html/core.html#aot[Spring AOT] native hints.
+For most common use cases, such as endpoint definitions with `@Bean` methods, Java DSL configuration with lambdas and `@MessagingGateway` interface scanning (importing), the framework provides respective reflection, proxy and serialization hints.
+If configuration uses messaging annotations (`@ServiceActivator`, `@Splitter` etc.) on POJO methods, or POJO methods are used with the `IntegrationFlowBuilder.handle(Object service, String methodName)` API, they have to be also marked with a `@Reflective` annotation since they are invoked by the framework reflectively.
+
+IMPORTANT: XML configuration is not supported for native images.
+
+As stated before, service interfaces with the `@MessagingGateway` annotation, when they are scanned by the `@IntegrationComponentScan` or used in an `@Import` annotation, are processed by the framework and the respective proxy hint is exposed into the AOT contribution.
+When gateways are declared using the `IntegrationFlow.from(Class<?> serviceInterface)` API, the proxy configured for such interfaces have to be exposed manually:
+
+====
+[source,java]
+----
+@Configuration
+@EnableIntegration
+@ImportRuntimeHints(GatewayRuntimeHints.class)
+public class IntegrationConfiguration {
+
+    @Bean
+    IntegrationFlow someFlow() {
+        return IntegrationFlow.from(SomeGateway)
+                  // ...
+                   .get();
+    }
+
+    public interface SomeGateway {
+
+        void doSomething(Object payload);
+
+    }
+
+    private static class GatewayRuntimeHints implements RuntimeHintsRegistrar {
+
+        @Override
+        public void registerHints(RuntimeHints hints, ClassLoader classLoader) {
+            hints.proxies().registerJdkProxy(
+                                   AopProxyUtils.completeJdkProxyInterfaces(SomeGateway));
+        }
+
+    }
+
+}
+----
+====
+
+NOTE: The `IntegrationFlow` content is not processed during the AOT processing phase.
+Therefore, some hints, such as the one mentioned above for a gateway proxy, must be provided by the target application.
+
+Of course, configuration is just a piece of an integration solution.
+The most important part is data transferring over the network as well as persistent storage.
+That's where serialization comes handy for many use-cases.
+Spring Integration exposes serialization hints into a native image configuration for these types used by the framework internally: `String`, `Number`, `Long`, `Date`, `ArrayList`, `HashMap`, `Properties`, `Hashtable`, `Exception`, `UUID`, `GenericMessage`, `ErrorMessage`, `MessageHeaders`, `AdviceMessage`, `MutableMessage`, `MutableMessageHeaders`, `MessageGroupMetadata`, `MessageHolder`, `MessageMetadata`, `MessageHistory`, `MessageHistory.Entry`, `DelayHandler.DelayedMessageWrapper`.
+For user specific data, mostly present as a message payload, the serialization hint must be exposed manually via a `RuntimeHintsRegistrar` implementation, as is shown above for a gateway proxy, and the respective `RuntimeHints.serialization().registerType()` API.
+
+NOTE: It is recommended that native integration applications are developed with Spring Boot, using its respective build tools.

src/reference/asciidoc/whats-new.adoc

@@ -52,7 +52,7 @@ The Java DSL (see `org.springframework.integration.smb.dsl.Smb` factory) also ha
 An `SmbStreamingMessageSource` and `SmbOutboundGateway` implementation are introduced.
 See <<./smb.adoc#smb,SMB Support>> for more information.
 
-[[x6.0-jdbc]]
+[[x6.0-postgres]]
 ==== PostgreSQL Push Notification
 
 A `PostgresSubscribableChannel` allows to receive push notifications via `PostgresChannelMessageTableSubscriber` upon new messages add to the `JdbcChannelMessageStore`.
@@ -98,6 +98,12 @@ Kotlin Coroutines support has been introduced to the framework.
 
 See <<./kotlin-functions.adoc#kotlin-coroutines,Kotlin Coroutines>> for more information.
 
+[[x6.0-aot]]
+==== Native Images
+
+Support for creating GraalVM native images is provided.
+See <<./native-aot.adoc#native-images-support,Native Images Support>> for more information.
+
 [[x6.0-general]]
 === General Changes
 
@@ -160,6 +166,7 @@ The `spring-integration-gemfire` module has been removed altogether since there
 The `#cookies` variable for expression evaluation context, exposed in the `HttpRequestHandlingEndpointSupport`, is now a `MultiValueMap` to carry all the values for cookies set by the client.
 See <<./http.adoc#http,HTTP Support>> for more information.
 
+[[x6.0-kafka]]
 === Apache Kafka Changes
 
 When providing a `RetryTemplate` on the inbound gateway or message-driven channel adapter, if an `errorChannel` is also provided, an `ErrorMessageSendingRecoverer` is automatically configured.
@@ -168,24 +175,28 @@ In addition, the new `KafkaErrorMessageSendingRecoverer` is provided; this can b
 
 See <<./kafka.adoc#kafka,Spring for Apache Kafka Support>> for more information.
 
+[[x6.0-jdbc]]
 === JDBC Changes
 
 The `DefaultLockRepository` can now be supplied with a `PlatformTransactionManager` instead of relying on the primary bean from the application context.
 
 See <<./jdbc.adoc#jdbc-lock-registry,JDBC Lock Registry>> for more information.
 
+[[x6.0-tcp]]
 === TCP/IP Changes
 
 The `lookupHost` property of the `AbstractConnectionFactory` and `DatagramPacketMessageMapper` is now set to `false` by default to avoid delays in the environments where DNS is not configured.
 
 See <<./ip.adoc#ip,TCP and UDP Support>> for more information.
 
+[[x6.0-jms]]
 === JMS Changes
 
 The `JmsOutboundGateway` now creates a `TemporaryTopic` instead of `TemporaryQueue` if `replyPubSubDomain` option is set to `true`.
 
 See <<./jms.adoc#jms,JMS Support>> for more information.
 
+[[x6.0-security]]
 === Security Changes
 
 The `ChannelSecurityInterceptor` and its annotation `@SecuredChannel` and XML `<secured-channels>` configurations have been deprecated in favor of `AuthorizationChannelInterceptor`.