Add RSocket Java DSL

* Add `@NonNullApi` for RSocket packages
* Some code style and JavaDocs polishing

spring-integration-rsocket/src/test/java/org/springframework/integration/rsocket/dsl/RSocketDslTests.java

@@ -0,0 +1,140 @@
+/*
+ * Copyright 2019 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.rsocket.dsl;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.util.function.Function;
+
+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.annotation.DependsOn;
+import org.springframework.core.codec.CharSequenceEncoder;
+import org.springframework.core.codec.StringDecoder;
+import org.springframework.core.io.buffer.NettyDataBufferFactory;
+import org.springframework.integration.config.EnableIntegration;
+import org.springframework.integration.dsl.IntegrationFlow;
+import org.springframework.integration.dsl.IntegrationFlows;
+import org.springframework.integration.rsocket.ClientRSocketConnector;
+import org.springframework.integration.rsocket.ServerRSocketConnector;
+import org.springframework.integration.rsocket.outbound.RSocketOutboundGateway;
+import org.springframework.messaging.rsocket.RSocketStrategies;
+import org.springframework.test.annotation.DirtiesContext;
+import org.springframework.test.context.junit.jupiter.SpringJUnitConfig;
+
+import io.netty.buffer.PooledByteBufAllocator;
+import io.netty.util.NetUtil;
+import io.rsocket.frame.decoder.PayloadDecoder;
+import io.rsocket.transport.netty.client.TcpClientTransport;
+import io.rsocket.transport.netty.server.TcpServerTransport;
+import reactor.core.publisher.Flux;
+import reactor.core.publisher.Mono;
+import reactor.netty.tcp.InetSocketAddressUtil;
+import reactor.netty.tcp.TcpClient;
+import reactor.netty.tcp.TcpServer;
+
+/**
+ * @author Artem Bilan
+ *
+ * @since 5.2
+ */
+@SpringJUnitConfig
+@DirtiesContext
+public class RSocketDslTests {
+
+	@Autowired
+	@Qualifier("rsocketUpperCaseRequestFlow.gateway")
+	private Function<String, String> rsocketUpperCaseFlowFunction;
+
+	@Test
+	void testRsocketUpperCaseFlows() {
+		assertThat(this.rsocketUpperCaseFlowFunction.apply("hello world")).isEqualTo("HELLO WORLD");
+	}
+
+	@Configuration
+	@EnableIntegration
+	public static class TestConfiguration {
+
+		private volatile int port;
+
+		@Bean
+		public RSocketStrategies rsocketStrategies() {
+			return RSocketStrategies.builder()
+					.decoder(StringDecoder.allMimeTypes())
+					.encoder(CharSequenceEncoder.allMimeTypes())
+					.dataBufferFactory(new NettyDataBufferFactory(PooledByteBufAllocator.DEFAULT))
+					.build();
+		}
+
+		@Bean
+		public ServerRSocketConnector serverRSocketConnector() {
+			TcpServer tcpServer =
+					TcpServer.create()
+							.port(0)
+							.doOnBound((server) -> this.port = server.port());
+			ServerRSocketConnector serverRSocketConnector =
+					new ServerRSocketConnector(TcpServerTransport.create(tcpServer));
+			serverRSocketConnector.setRSocketStrategies(rsocketStrategies());
+			serverRSocketConnector.setFactoryConfigurer((factory) -> factory.frameDecoder(PayloadDecoder.ZERO_COPY));
+			return serverRSocketConnector;
+		}
+
+
+		@Bean
+		@DependsOn("serverRSocketConnector")
+		public ClientRSocketConnector clientRSocketConnector() {
+			ClientRSocketConnector clientRSocketConnector =
+					new ClientRSocketConnector(
+							TcpClientTransport.create(
+									TcpClient.create()
+											.addressSupplier(() ->
+													InetSocketAddressUtil.createUnresolved(
+															NetUtil.LOCALHOST.getHostAddress(), this.port))
+							));
+			clientRSocketConnector.setFactoryConfigurer((factory) -> factory.frameDecoder(PayloadDecoder.ZERO_COPY));
+			clientRSocketConnector.setRSocketStrategies(rsocketStrategies());
+			clientRSocketConnector.setAutoStartup(false);
+			return clientRSocketConnector;
+		}
+
+		@Bean
+		public IntegrationFlow rsocketUpperCaseRequestFlow() {
+			return IntegrationFlows
+					.from(Function.class)
+					.handle(RSockets.outboundGateway("/uppercase")
+							.command((message) -> RSocketOutboundGateway.Command.requestResponse)
+							.expectedResponseType("T(java.lang.String)")
+							.clientRSocketConnector(clientRSocketConnector()))
+					.get();
+		}
+
+		@Bean
+		public IntegrationFlow rsocketUpperCaseFlow() {
+			return IntegrationFlows
+					.from(RSockets.inboundGateway("/uppercase")
+							.rsocketStrategies(rsocketStrategies()))
+					.<Flux<String>, Mono<String>>transform((flux) -> flux.next().map(String::toUpperCase))
+					.get();
+		}
+
+	}
+
+}