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-context/src/main/java/org/springframework/cloud/function/context/AbstractFunctionRegistry.java

@@ -0,0 +1,44 @@
+/*
+ * 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.context;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.core.env.Environment;
+import org.springframework.core.env.StandardEnvironment;
+import org.springframework.util.StringUtils;
+
+/**
+ *
+ * @author Oleg Zhurakousky
+ *
+ * @since 2.0.1
+ *
+ */
+public abstract class AbstractFunctionRegistry implements FunctionRegistry {
+
+	@Autowired
+	private Environment environment = new StandardEnvironment();
+
+
+	public <T> T lookup(Class<?> type, String name) {
+		String functionDefinitionName = !StringUtils.hasText(name) && environment.containsProperty("spring.cloud.function.definition")
+				? environment.getProperty("spring.cloud.function.definition") : name;
+		return this.doLookup(type, functionDefinitionName);
+	}
+
+	protected abstract <T> T doLookup(Class<?> type, String name);
+}

spring-cloud-function-context/src/main/java/org/springframework/cloud/function/context/catalog/InMemoryFunctionCatalog.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2018 the original author or authors.
+ * Copyright 2016-2019 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.
@@ -28,8 +28,8 @@ import java.util.stream.Collectors;
 import javax.annotation.PostConstruct;
 import javax.annotation.PreDestroy;
 
+import org.springframework.cloud.function.context.AbstractFunctionRegistry;
 import org.springframework.cloud.function.context.FunctionRegistration;
-import org.springframework.cloud.function.context.FunctionRegistry;
 import org.springframework.context.ApplicationEventPublisher;
 import org.springframework.context.ApplicationEventPublisherAware;
 import org.springframework.util.Assert;
@@ -39,8 +39,8 @@ import org.springframework.util.Assert;
  * @author Mark Fisher
  * @author Oleg Zhurakousky
  */
-public class InMemoryFunctionCatalog
-		implements FunctionRegistry, FunctionInspector, ApplicationEventPublisherAware {
+public class InMemoryFunctionCatalog extends AbstractFunctionRegistry
+		implements FunctionInspector, ApplicationEventPublisherAware {
 
 	private final Map<Class<?>, Map<String, Object>> functions;
 
@@ -122,7 +122,7 @@ public class InMemoryFunctionCatalog
 
 	@Override
 	@SuppressWarnings("unchecked")
-	public <T> T lookup(Class<?> type, String name) {
+	public <T> T doLookup(Class<?> type, String name) {
 		T function = null;
 		if (type == null) {
 			function = (T) functions.values().stream()

spring-cloud-function-context/src/main/java/org/springframework/cloud/function/context/config/ContextFunctionCatalogAutoConfiguration.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2018 the original author or authors.
+ * Copyright 2016-2019 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.
@@ -41,6 +41,7 @@ import org.springframework.boot.autoconfigure.condition.ConditionalOnBean;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
+import org.springframework.cloud.function.context.AbstractFunctionRegistry;
 import org.springframework.cloud.function.context.FunctionCatalog;
 import org.springframework.cloud.function.context.FunctionRegistration;
 import org.springframework.cloud.function.context.FunctionRegistry;
@@ -103,6 +104,8 @@ public class ContextFunctionCatalogAutoConfiguration {
 	@Autowired(required = false)
 	private Map<String, FunctionRegistration<?>> registrations = Collections.emptyMap();
 
+
+
 	@Bean
 	public FunctionRegistry functionCatalog(ContextFunctionRegistry processor) {
 		processor.merge(registrations, consumers, suppliers, functions);
@@ -114,7 +117,7 @@ public class ContextFunctionCatalogAutoConfiguration {
 		return new BeanFactoryFunctionInspector(processor);
 	}
 
-	protected static class BeanFactoryFunctionCatalog implements FunctionRegistry {
+	protected static class BeanFactoryFunctionCatalog extends AbstractFunctionRegistry {
 
 		private final ContextFunctionRegistry processor;
 
@@ -127,7 +130,7 @@ public class ContextFunctionCatalogAutoConfiguration {
 
 		@Override
 		@SuppressWarnings("unchecked")
-		public <T> T lookup(Class<?> type, String name) {
+		protected <T> T doLookup(Class<?> type, String name) {
 			T function = null;
 			if (type == null) {
 				function = (T) processor.lookupFunction(name);

spring-cloud-function-context/src/main/resources/META-INF/spring-configuration-metadata.json

@@ -7,6 +7,12 @@
         "type": "java.lang.String",
         "description": "Triggers scanning within the specified base packages for any class that is assignable to java.util.function.Function. For each detected Function class, a bean instance will be added to the context.",
         "defaultValue": "functions"
+    },
+    {
+        "name": "spring.cloud.function.definition",
+        "type": "java.lang.String",
+        "description": "Name (e.g., 'foo') or composition instruction (e.g., 'foo|bar') used to resolve default function especially for cases where there is more then once function available in catalog.",
+        "defaultValue": ""
     }
   ]
 }