GH-247 Added spring.cloud.function.definition property

Added spring.cloud.function.definition property which is used by FunctionRegistry as a supplement instruction to resolve nameless lookups.
It is used by web module to map single or multiple (composed) functions to the root path (/)

Resolves #247

spring-cloud-function-web/src/test/java/org/springframework/cloud/function/test/MoreThenOneFunctionRootMappingTests.java

@@ -0,0 +1,69 @@
+/*
+ * 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
+ *
+ *      http://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.cloud.function.test;
+
+import java.util.function.Function;
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.SpringBootConfiguration;
+import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
+import org.springframework.boot.test.autoconfigure.web.reactive.AutoConfigureWebTestClient;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.context.annotation.Bean;
+import org.springframework.test.annotation.DirtiesContext;
+import org.springframework.test.context.junit4.SpringRunner;
+import org.springframework.test.web.reactive.server.WebTestClient;
+
+import reactor.core.publisher.Mono;
+
+/**
+ * @author Oleg Zhurakousky
+ *
+ */
+@RunWith(SpringRunner.class)
+@SpringBootTest({ "spring.main.web-application-type=REACTIVE",
+		"spring.functional.enabled=false",
+		"spring.cloud.function.definition=uppercase|reverse"})
+@AutoConfigureWebTestClient
+@DirtiesContext
+public class MoreThenOneFunctionRootMappingTests {
+
+	@Autowired
+	private WebTestClient client;
+
+	@Test
+	public void words() throws Exception {
+		client.post().uri("/").body(Mono.just("star"), String.class).exchange()
+				.expectStatus().isOk().expectBody(String.class).isEqualTo("RATS");
+	}
+
+	@SpringBootConfiguration
+	@EnableAutoConfiguration
+	protected static class TestConfiguration {
+		@Bean
+		public Function<String, String> uppercase() {
+			return v -> v.toUpperCase();
+		}
+
+		@Bean
+		public Function<String, String> reverse() {
+			return v -> new StringBuilder(v).reverse().toString();
+		}
+	}
+}