Tweak logic in stream invokers

* If there is only one function, use it unconditionally
* If no functions match, ensure that null is not the selector
* If a conversion succeeds, check the type of the result

spring-cloud-function-stream/src/main/java/org/springframework/cloud/function/stream/StreamListeningConsumerInvoker.java

@@ -48,6 +48,8 @@ public class StreamListeningConsumerInvoker implements SmartInitializingSingleto
 
 	private final String[] names;
 
+	private static final String NOENDPOINT = "__NOENDPOINT__";
+
 	public StreamListeningConsumerInvoker(FunctionCatalog functionCatalog,
 			FunctionInspector functionInspector,
 			CompositeMessageConverterFactory converterFactory, String defaultEndpoint,
@@ -79,14 +81,23 @@ public class StreamListeningConsumerInvoker implements SmartInitializingSingleto
 	private String select(Message<?> input) {
 		String name = defaultEndpoint;
 		if (name == null) {
-			for (String candidate : names) {
-				Class<?> inputType = functionInspector.getInputType(candidate);
-				if (this.converter.fromMessage(input, inputType) != null) {
-					name = candidate;
-					break;
+			if (names.length == 1) {
+				name = names[0];
+			}
+			else {
+				for (String candidate : names) {
+					Class<?> inputType = functionInspector.getInputType(candidate);
+					Object value = this.converter.fromMessage(input, inputType);
+					if (value != null && inputType.isInstance(value)) {
+						name = candidate;
+						break;
+					}
 				}
 			}
 		}
+		if (name == null) {
+			return NOENDPOINT;
+		}
 		return name;
 	}
 

spring-cloud-function-stream/src/main/java/org/springframework/cloud/function/stream/StreamListeningFunctionInvoker.java

@@ -50,6 +50,8 @@ public class StreamListeningFunctionInvoker implements SmartInitializingSingleto
 
 	private final String[] names;
 
+	private static final String NOENDPOINT = "__NOENDPOINT__";
+
 	public StreamListeningFunctionInvoker(FunctionCatalog functionCatalog,
 			FunctionInspector functionInspector,
 			CompositeMessageConverterFactory converterFactory, String defaultEndpoint,
@@ -82,14 +84,23 @@ public class StreamListeningFunctionInvoker implements SmartInitializingSingleto
 	private String select(Message<?> input) {
 		String name = defaultEndpoint;
 		if (name == null) {
-			for (String candidate : names) {
-				Class<?> inputType = functionInspector.getInputType(candidate);
-				if (this.converter.fromMessage(input, inputType) != null) {
-					name = candidate;
-					break;
+			if (names.length == 1) {
+				name = names[0];
+			}
+			else {
+				for (String candidate : names) {
+					Class<?> inputType = functionInspector.getInputType(candidate);
+					Object value = this.converter.fromMessage(input, inputType);
+					if (value != null && inputType.isInstance(value)) {
+						name = candidate;
+						break;
+					}
 				}
 			}
 		}
+		if (name == null) {
+			return NOENDPOINT;
+		}
 		return name;
 	}
 

spring-cloud-function-stream/src/test/java/org/springframework/cloud/function/stream/function/FluxPojoStreamingFunctionConversionTests.java

@@ -0,0 +1,162 @@
+/*
+ * Copyright 2017 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.stream.function;
+
+import java.io.Serializable;
+import java.util.concurrent.TimeUnit;
+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.autoconfigure.SpringBootApplication;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.cloud.stream.converter.MessageConverterUtils;
+import org.springframework.cloud.stream.messaging.Processor;
+import org.springframework.cloud.stream.test.binder.MessageCollector;
+import org.springframework.context.annotation.Bean;
+import org.springframework.messaging.Message;
+import org.springframework.messaging.support.MessageBuilder;
+import org.springframework.test.context.junit4.SpringRunner;
+import org.springframework.util.SerializationUtils;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import reactor.core.publisher.Flux;
+
+/**
+ * @author Marius Bogoevici
+ */
+@RunWith(SpringRunner.class)
+@SpringBootTest(classes = FluxPojoStreamingFunctionConversionTests.StreamingFunctionApplication.class)
+public class FluxPojoStreamingFunctionConversionTests {
+
+	@Autowired
+	Processor processor;
+
+	@Autowired
+	MessageCollector messageCollector;
+
+	@Test
+	public void foo() throws Exception {
+		processor.input().send(MessageBuilder
+				.withPayload(SerializationUtils.serialize(new Foo("foo")))
+				.setHeader("contentType", MessageConverterUtils.X_JAVA_SERIALIZED_OBJECT)
+				.build());
+		Message<?> result = messageCollector.forChannel(processor.output()).poll(1000,
+				TimeUnit.MILLISECONDS);
+		assertThat(result.getPayload()).isInstanceOf(Foo.class);
+	}
+
+	@Test
+	public void bar() throws Exception {
+		processor.input().send(MessageBuilder
+				.withPayload(SerializationUtils.serialize(new Bar("foo")))
+				.setHeader("contentType", MessageConverterUtils.X_JAVA_SERIALIZED_OBJECT)
+				.build());
+		Message<?> result = messageCollector.forChannel(processor.output()).poll(1000,
+				TimeUnit.MILLISECONDS);
+		assertThat(result.getPayload()).isInstanceOf(Bar.class);
+	}
+
+	@Test
+	public void skip() throws Exception {
+		processor.input().send(MessageBuilder
+				.withPayload(SerializationUtils.serialize(new Spam("foo")))
+				.setHeader("contentType", MessageConverterUtils.X_JAVA_SERIALIZED_OBJECT)
+				.build());
+		Message<?> result = messageCollector.forChannel(processor.output()).poll(100,
+				TimeUnit.MILLISECONDS);
+		assertThat(result).isNull();
+	}
+
+	@SpringBootApplication
+	public static class StreamingFunctionApplication {
+
+		@Bean
+		public Function<Flux<Foo>, Flux<Foo>> uppercase() {
+			return foos -> foos.map(f -> new Foo(f.getName().toUpperCase()));
+		}
+
+		@Bean
+		public Function<Flux<Bar>, Flux<Bar>> lowercase() {
+			return foos -> foos.map(f -> new Bar(f.getName().toUpperCase()));
+		}
+
+	}
+
+	@SuppressWarnings("serial")
+	protected static class Foo implements Serializable {
+		private String name;
+
+		Foo() {
+		}
+
+		public Foo(String name) {
+			this.name = name;
+		}
+
+		public String getName() {
+			return name;
+		}
+
+		public void setName(String name) {
+			this.name = name;
+		}
+	}
+
+	@SuppressWarnings("serial")
+	protected static class Bar implements Serializable {
+		private String name;
+
+		Bar() {
+		}
+
+		public Bar(String name) {
+			this.name = name;
+		}
+
+		public String getName() {
+			return name;
+		}
+
+		public void setName(String name) {
+			this.name = name;
+		}
+	}
+
+	@SuppressWarnings("serial")
+	protected static class Spam implements Serializable {
+		private String name;
+
+		Spam() {
+		}
+
+		public Spam(String name) {
+			this.name = name;
+		}
+
+		public String getName() {
+			return name;
+		}
+
+		public void setName(String name) {
+			this.name = name;
+		}
+	}
+}

spring-cloud-function-stream/src/test/java/org/springframework/cloud/function/stream/function/FluxPojoStreamingFunctionTests.java

@@ -21,7 +21,6 @@ import java.util.function.Function;
 
 import org.junit.Test;
 import org.junit.runner.RunWith;
-import reactor.core.publisher.Flux;
 
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.boot.autoconfigure.SpringBootApplication;
@@ -35,6 +34,8 @@ import org.springframework.test.context.junit4.SpringRunner;
 
 import static org.assertj.core.api.Assertions.assertThat;
 
+import reactor.core.publisher.Flux;
+
 /**
  * @author Marius Bogoevici
  */
@@ -62,6 +63,7 @@ public class FluxPojoStreamingFunctionTests {
 		public Function<Flux<Foo>, Flux<Foo>> uppercase() {
 			return foos -> foos.map(f -> new Foo(f.getName().toUpperCase()));
 		}
+
 	}
 
 	protected static class Foo {