Add Java DSL for Camel module and docs (#3937)

* Add Java DSL for Camel module and docs

* Introduce a `LambdaRouteBuilder` option into the `CamelMessageHandler`
to easily provide the Camel route just in-place

* * Fix language in docs

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

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

spring-integration-camel/src/test/java/org/springframework/integration/camel/dsl/CamelDslTests.java

@@ -0,0 +1,90 @@
+/*
+ * Copyright 2022 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.integration.camel.dsl;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import org.apache.camel.CamelContext;
+import org.apache.camel.builder.RouteBuilder;
+import org.apache.camel.spring.SpringCamelContext;
+import org.junit.jupiter.api.Test;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.beans.factory.annotation.Qualifier;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.context.event.ContextRefreshedEvent;
+import org.springframework.context.event.EventListener;
+import org.springframework.integration.config.EnableIntegration;
+import org.springframework.integration.core.MessagingTemplate;
+import org.springframework.integration.dsl.IntegrationFlow;
+import org.springframework.messaging.MessageChannel;
+import org.springframework.test.annotation.DirtiesContext;
+import org.springframework.test.context.junit.jupiter.SpringJUnitConfig;
+
+/**
+ * @author Artem Bilan
+ *
+ * @since 6.0
+ */
+@SpringJUnitConfig
+@DirtiesContext
+public class CamelDslTests {
+
+	@Autowired
+	@Qualifier("camelFlow.input")
+	MessageChannel input;
+
+	@Test
+	void sendAndReceiveCamelRoute() {
+		String result = new MessagingTemplate().convertSendAndReceive(this.input, "apache camel", String.class);
+		assertThat(result).isEqualTo("___APACHE CAMEL___");
+	}
+
+	@Configuration
+	@EnableIntegration
+	public static class Config {
+
+		@Bean
+		CamelContext springCamelContext() {
+			return new SpringCamelContext();
+		}
+
+		@EventListener(ContextRefreshedEvent.class)
+		public void simpleRoute() throws Exception {
+			RouteBuilder.addRoutes(springCamelContext(),
+					rb -> rb.from("direct:simple").bean("camelDslTests.Config", "transformPayload"));
+		}
+
+		@Bean
+		IntegrationFlow camelFlow() {
+			return f -> f
+					.handle(Camel.gateway().endpointUri("direct:simple"))
+					.handle(Camel.route(this::camelRoute));
+		}
+
+		private void camelRoute(RouteBuilder routeBuilder) {
+			routeBuilder.from("direct:inbound").transform(routeBuilder.simple("${body.toUpperCase()}"));
+		}
+
+		public String transformPayload(String payload) {
+			return "___" + payload + "___";
+		}
+
+	}
+
+}

spring-integration-camel/src/test/java/org/springframework/integration/camel/outbound/CamelMessageHandlerTests.java

@@ -183,6 +183,7 @@ public class CamelMessageHandlerTests extends CamelTestSupport {
 			public void configure() {
 				from("direct:simple").to("mock:result");
 			}
+
 		};
 	}