Add support for empty function.bean

If there is a unique function it should be unambiguous. This change
also supports multiple functions, but the naming is unhelpful then
("function[0,1,2,]").

spring-cloud-function-deployer/src/main/java/org/springframework/cloud/function/deployer/ApplicationRunner.java

@@ -16,8 +16,10 @@
 
 package org.springframework.cloud.function.deployer;
 
+import java.util.Collections;
 import java.util.HashMap;
 import java.util.Map;
+import java.util.Set;
 import java.util.UUID;
 
 import javax.annotation.PreDestroy;
@@ -144,6 +146,28 @@ public class ApplicationRunner {
 		return false;
 	}
 
+	/**
+	 * List the bean names in the application context for a given type (by its fully qualified name).
+	 * 
+	 * @param type the name of the type (Class)
+	 * @return the bean names of that type
+	 */
+	public Set<String> getBeanNames(String type) {
+		if (this.app != null) {
+			Expression parsed = new SpelExpressionParser()
+					.parseExpression("context.getBeansOfType(T(" + type + "))");
+			try {
+				@SuppressWarnings("unchecked")
+				Map<String, Object> beans = (Map<String, Object>) parsed
+						.getValue(this.app);
+				return beans.keySet();
+			}
+			catch (Exception e) {
+			}
+		}
+		return Collections.emptySet();
+	}
+
 	public Object evaluate(String expression, Object root, Object... attrs) {
 		Expression parsed = new SpelExpressionParser(this.config)
 				.parseExpression(expression);

spring-cloud-function-deployer/src/main/java/org/springframework/cloud/function/deployer/FunctionCreatorConfiguration.java

@@ -25,7 +25,9 @@ import java.net.URLClassLoader;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collections;
+import java.util.LinkedHashSet;
 import java.util.List;
+import java.util.Set;
 import java.util.StringTokenizer;
 import java.util.concurrent.atomic.AtomicInteger;
 import java.util.function.Consumer;
@@ -114,7 +116,7 @@ class FunctionCreatorConfiguration {
 					"Locating function from " + Arrays.asList(properties.getLocation()));
 			this.creator = new BeanCreator(urls);
 			this.creator.run(properties.getMain());
-			Arrays.stream(properties.getBean()).map(this.creator::create).sequential()
+			Arrays.stream(functionNames()).map(this.creator::create).sequential()
 					.forEach(this.creator::register);
 			if (properties.getName().contains("|")) {
 				// A composite function has to be explicitly registered before it is
@@ -129,6 +131,13 @@ class FunctionCreatorConfiguration {
 		}
 	}
 
+	private String[] functionNames() {
+		if (properties.getBean() != null && properties.getBean().length > 0) {
+			return properties.getBean();
+		}
+		return this.creator.getFunctionNames();
+	}
+
 	@PreDestroy
 	public void close() {
 		if (this.creator != null) {
@@ -375,6 +384,38 @@ class FunctionCreatorConfiguration {
 			}
 		}
 
+		public String[] getFunctionNames() {
+			Set<String> list = new LinkedHashSet<>();
+			ClassLoader contextClassLoader = ClassUtils
+					.overrideThreadContextClassLoader(functionClassLoader);
+			try {
+				if (this.runner.containsBean(FunctionCatalog.class.getName())) {
+					Object catalog = this.runner.getBean(FunctionCatalog.class.getName());
+					@SuppressWarnings("unchecked")
+					Set<String> functions = (Set<String>) this.runner
+							.evaluate("getNames(#type)", catalog, "type", Function.class);
+					list.addAll(functions);
+					@SuppressWarnings("unchecked")
+					Set<String> consumers = (Set<String>) this.runner
+							.evaluate("getNames(#type)", catalog, "type", Consumer.class);
+					list.addAll(consumers);
+					@SuppressWarnings("unchecked")
+					Set<String> suppliers = (Set<String>) this.runner
+							.evaluate("getNames(#type)", catalog, "type", Supplier.class);
+					list.addAll(suppliers);
+				}
+				if (list.isEmpty()) {
+					list.addAll(this.runner.getBeanNames(Function.class.getName()));
+					list.addAll(this.runner.getBeanNames(Consumer.class.getName()));
+					list.addAll(this.runner.getBeanNames(Supplier.class.getName()));
+				}
+				return list.toArray(new String[0]);
+			}
+			finally {
+				ClassUtils.overrideThreadContextClassLoader(contextClassLoader);
+			}
+		}
+
 		public Object create(String type) {
 			ClassLoader contextClassLoader = ClassUtils
 					.overrideThreadContextClassLoader(functionClassLoader);

spring-cloud-function-deployer/src/main/java/org/springframework/cloud/function/deployer/FunctionProperties.java

@@ -95,9 +95,5 @@ public class FunctionProperties {
 			throw new IllegalStateException(
 					"No archive location provided, please configure function.location as a jar or directory.");
 		}
-		if (bean.length == 0) {
-			throw new IllegalStateException(
-					"No function bean locator provided, please configure function.bean as a bean name or class name.");
-		}
 	}
 }

spring-cloud-function-deployer/src/test/java/org/springframework/cloud/function/deployer/ApplicationRunnerTests.java

@@ -20,6 +20,7 @@ import org.junit.Ignore;
 import org.junit.Test;
 
 import org.springframework.cloud.function.context.FunctionCatalog;
+import org.springframework.cloud.function.context.FunctionRegistration;
 import org.springframework.cloud.function.test.Doubler;
 import org.springframework.cloud.function.test.FunctionApp;
 import org.springframework.cloud.function.test.FunctionRegistrar;
@@ -43,14 +44,13 @@ public class ApplicationRunnerTests {
 	}
 
 	@Test
-	@Ignore // related to boot 2.1 no bean override change
 	public void functional() {
 		ApplicationRunner runner = new ApplicationRunner(getClass().getClassLoader(),
 				FunctionRegistrar.class.getName());
 		runner.run();
-		assertThat(runner.containsBean(Doubler.class.getName())).isTrue();
-		assertThat(runner.getBean(Doubler.class.getName())).isNotNull();
+		assertThat(runner.containsBean(Doubler.class.getName())).isFalse();
 		assertThat(runner.getBean(FunctionCatalog.class.getName())).isNotNull();
+		assertThat(runner.getBeanNames(FunctionRegistration.class.getName())).hasSize(2);
 		runner.close();
 	}
 }