GH-77 added initial Kotlin support

Added mixed java/kotlin POM configuration

added tests, javadocs

Resolves #77
Resolves #204

spring-cloud-function-context/src/test/java/org/springframework/cloud/function/context/config/ContextFunctionCatalogAutoConfigurationTests.java

@@ -27,6 +27,8 @@ import java.util.function.Function;
 import java.util.function.Supplier;
 import java.util.stream.Collectors;
 
+import kotlin.jvm.functions.Function0;
+import kotlin.jvm.functions.Function1;
 import org.junit.After;
 import org.junit.Test;
 import org.reactivestreams.Publisher;
@@ -48,6 +50,7 @@ import org.springframework.cloud.function.context.FunctionRegistration;
 import org.springframework.cloud.function.context.FunctionScan;
 import org.springframework.cloud.function.context.catalog.FunctionInspector;
 import org.springframework.cloud.function.inject.FooConfiguration;
+import org.springframework.cloud.function.kotlin.KotlinLambdasConfiguration;
 import org.springframework.cloud.function.scan.ScannedFunction;
 import org.springframework.cloud.function.test.GenericFunction;
 import org.springframework.context.ConfigurableApplicationContext;
@@ -372,6 +375,34 @@ public class ContextFunctionCatalogAutoConfigurationTests {
 		}
 	}
 
+	@Test
+	public void kotlinLambdas() {
+		create(KotlinLambdasConfiguration.class);
+
+		assertThat(context.getBean("kotlinFunction")).isInstanceOf(Function.class);
+		assertThat(context.getBean("kotlinFunction")).isInstanceOf(Function1.class);
+		assertThat(catalog.lookup(Function.class, "kotlinFunction"))
+				.isInstanceOf(Function.class);
+		assertThat(inspector.getInputType(catalog.lookup(Function.class, "kotlinFunction")))
+				.isAssignableFrom(String.class);
+		assertThat(inspector.getOutputType(catalog.lookup(Function.class, "kotlinFunction")))
+				.isAssignableFrom(String.class);
+
+		assertThat(context.getBean("kotlinConsumer")).isInstanceOf(Consumer.class);
+		assertThat(context.getBean("kotlinConsumer")).isInstanceOf(Function1.class);
+		assertThat(catalog.lookup(Function.class, "kotlinConsumer"))
+				.isInstanceOf(Function.class);
+		assertThat(inspector.getInputType(catalog.lookup(Function.class, "kotlinConsumer")))
+				.isAssignableFrom(String.class);
+
+		assertThat(context.getBean("kotlinSupplier")).isInstanceOf(Supplier.class);
+		assertThat(context.getBean("kotlinSupplier")).isInstanceOf(Function0.class);
+		assertThat(catalog.lookup(Supplier.class, "kotlinSupplier"))
+				.isInstanceOf(Supplier.class);
+		assertThat(inspector.getOutputType(catalog.lookup(Supplier.class, "kotlinSupplier")))
+				.isAssignableFrom(String.class);
+	}
+
 	private void create(String jarfile, Class<?> config, String... props) {
 		try {
 			URL[] urls = new URL[] { new ClassPathResource(jarfile).getURL() };

spring-cloud-function-context/src/test/kotlin/org/springframework/cloud/function/kotlin/KotlinLambdasConfiguration.kt

@@ -0,0 +1,44 @@
+/*
+ * Copyright 2018 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.kotlin
+
+import org.springframework.boot.autoconfigure.EnableAutoConfiguration
+import org.springframework.context.annotation.Bean
+import org.springframework.context.annotation.Configuration
+
+/**
+ * @author Oleg Zhurakousky
+ *
+ */
+@EnableAutoConfiguration
+@Configuration
+open class KotlinLambdasConfiguration {
+    @Bean
+    open fun kotlinFunction(): (String) -> String {
+        return  { it.toUpperCase() }
+    }
+
+    @Bean
+    open fun kotlinConsumer(): (String) -> Unit {
+        return  { }
+    }
+
+    @Bean
+    open fun kotlinSupplier(): () -> String {
+        return  { "Hello" }
+    }
+}