GH-653 Add documentation and additional test to validate function definition order for RSocket

Resolves #653

spring-cloud-function-rsocket/README.md

@@ -13,9 +13,8 @@ adjustment needed to apply proper invocation model to the framework.
 To use RSocket integration all you need is to add `spring-cloud-function-rsocket` dependency to your classpath
 ```
 <dependency>
-            <groupId>org.springframework.cloud</groupId>
-            <artifactId>spring-cloud-function-rsocket</artifactId>
-            <version>3.1.0</version>
+	<groupId>org.springframework.cloud</groupId>
+	<artifactId>spring-cloud-function-rsocket</artifactId>
  </dependency>
 ```
 
@@ -56,4 +55,21 @@ rsocketRequesterBuilder.tcp("localhost", port)
 	.subscribe(System.out::println);
 ```
 
+### Function Definitions
+
+As you can see from the preceding example, we provide function definition as a value to `route(..)` operator of `RSocketRequester.Builder`.
+However that is not the only way. You can also use standard `spring.cloud.function.definition` property as well as `spring.cloud.function.routing-expression` property. 
+This raises a question of _order_ and _priorities_ when it comes to reconsiling a conflict in the event several ways of providing definition are used. So it is a mater of clearly stating the rule whcih is:
+
+***1 - spring.cloud.function.routing-expression***
+The `spring.cloud.function.routing-expression` property takes precedence over all other ways of providing definition. So, in the event you may have also use `route(..)` operator or `spring.cloud.function.definition` property, they will be ignored if `spring.cloud.function.routing-expression` property is provided.
+
+***2 - route(..)***
+The next in line is `route(..)` operator. So in the event there are no `spring.cloud.function.routing-expression` property but you defined `spring.cloud.function.definition` property, it will be ignored in favor of definition provided by the `route(..)` operator.
+
+***3 - spring.cloud.function.definition***
+The `spring.cloud.function.definition` property is the last in the list allowing you to simply `route("")` to empty string.
+
+
+
 You can also look at one of the [RSocket samples](https://github.com/spring-cloud/spring-cloud-function/tree/master/spring-cloud-function-samples/function-sample-cloudevent-rsocket) that is also introduces you to Cloud Events 

spring-cloud-function-rsocket/src/test/java/org/springframework/cloud/function/rsocket/RSocketAutoConfigurationRoutingTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2020-2020 the original author or authors.
+ * Copyright 2021-2021 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.
@@ -43,7 +43,7 @@ import org.springframework.util.SocketUtils;
  */
 public class RSocketAutoConfigurationRoutingTests {
 	@Test
-	public void testImperativeFunctionAsRequestReplyWithDefinition() {
+	public void testRoutingWithRoute() {
 		int port = SocketUtils.findAvailableTcpPort();
 		try (
 			ConfigurableApplicationContext applicationContext =
@@ -87,18 +87,60 @@ public class RSocketAutoConfigurationRoutingTests {
 				.expectComplete()
 				.verify();
 
-//			rsocketRequesterBuilder.tcp("localhost", port)
-//				.route(RoutingFunction.FUNCTION_NAME)
-//				.metadata("{\"func_name\":\"uppercase\"}", MimeTypeUtils.APPLICATION_JSON)
-//				.data("hello")
-//				.retrieveMono(String.class)
-//				.as(StepVerifier::create)
-//				.expectNext("HELLO")
-//				.expectComplete()
-//				.verify();
 		}
 	}
 
+	@Test
+	public void testRoutingWithDefinition() {
+		int port = SocketUtils.findAvailableTcpPort();
+		try (
+			ConfigurableApplicationContext applicationContext =
+				new SpringApplicationBuilder(SampleFunctionConfiguration.class)
+					.web(WebApplicationType.NONE)
+					.run("--logging.level.org.springframework.cloud.function=DEBUG",
+							"--spring.cloud.function.definition=uppercase",
+							"--spring.cloud.function.routing-expression=headers.func_name",
+							"--spring.cloud.function.expected-content-type=text/plain",
+							"--spring.rsocket.server.port=" + port);
+		) {
+			RSocketRequester.Builder rsocketRequesterBuilder =
+				applicationContext.getBean(RSocketRequester.Builder.class);
+
+			rsocketRequesterBuilder.tcp("localhost", port)
+				.route("uppercase")
+				.metadata("{\"func_name\":\"echo\"}", MimeTypeUtils.APPLICATION_JSON)
+				.data("hello")
+				.retrieveMono(String.class)
+				.as(StepVerifier::create)
+				.expectNext("hello")
+				.expectComplete()
+				.verify();
+
+			rsocketRequesterBuilder.tcp("localhost", port)
+				.route("")
+				.metadata("{\"func_name\":\"echo\"}", MimeTypeUtils.APPLICATION_JSON)
+				.data("hello")
+				.retrieveMono(String.class)
+				.as(StepVerifier::create)
+				.expectNext("hello")
+				.expectComplete()
+				.verify();
+
+			rsocketRequesterBuilder.tcp("localhost", port)
+				.route(RoutingFunction.FUNCTION_NAME)
+				.metadata("{\"func_name\":\"echo\"}", MimeTypeUtils.APPLICATION_JSON)
+				.data("hello")
+				.retrieveMono(String.class)
+				.as(StepVerifier::create)
+				.expectNext("hello")
+				.expectComplete()
+				.verify();
+
+		}
+	}
+
+
+
 
 	@EnableAutoConfiguration
 	@Configuration