Use Void as input type for Supplier, etc.

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

@@ -18,7 +18,9 @@ package org.springframework.cloud.function.context;
 import java.lang.reflect.ParameterizedType;
 import java.lang.reflect.Type;
 import java.util.Optional;
+import java.util.function.Consumer;
 import java.util.function.Function;
+import java.util.function.Supplier;
 
 import org.reactivestreams.Publisher;
 
@@ -219,6 +221,9 @@ public class FunctionType {
 		if (type instanceof ParameterizedType) {
 			ParameterizedType parameterizedType = (ParameterizedType) type;
 			if (parameterizedType.getActualTypeArguments().length == 1) {
+				if (isVoid(parameterizedType, paramType)) {
+					return Void.class;
+				}
 				// There's only one
 				index = 0;
 			}
@@ -245,6 +250,17 @@ public class FunctionType {
 		return param;
 	}
 
+	private boolean isVoid(ParameterizedType parameterizedType, ParamType paramType) {
+		Class<?> rawType = extractClass(parameterizedType.getRawType(), paramType);
+		if (Consumer.class.isAssignableFrom(rawType) && paramType.isOutput()) {
+			return true;
+		}
+		if (Supplier.class.isAssignableFrom(rawType) && paramType.isInput()) {
+			return true;
+		}
+		return false;
+	}
+
 	private Type extractNestedType(ParamType paramType, Type param) {
 		if (!paramType.isInnerWrapper() && param instanceof ParameterizedType) {
 			if (((ParameterizedType) param).getRawType().getTypeName()

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

@@ -18,7 +18,9 @@ package org.springframework.cloud.function.context;
 import java.lang.reflect.Type;
 import java.util.Collections;
 import java.util.Map;
+import java.util.function.Consumer;
 import java.util.function.Function;
+import java.util.function.Supplier;
 
 import org.junit.Test;
 
@@ -99,6 +101,30 @@ public class FunctionTypeTests {
 		assertThat(function.isMessage()).isEqualTo(false);
 	}
 
+	@Test
+	public void pojoConsumerFromType() {
+		Type type = ResolvableType.forClassWithGenerics(Consumer.class, Foo.class)
+				.getType();
+		FunctionType function = new FunctionType(type);
+		assertThat(function.getInputType()).isEqualTo(Foo.class);
+		assertThat(function.getOutputType()).isEqualTo(Void.class);
+		assertThat(function.getInputWrapper()).isEqualTo(Foo.class);
+		assertThat(function.getOutputWrapper()).isEqualTo(Void.class);
+		assertThat(function.isMessage()).isEqualTo(false);
+	}
+
+	@Test
+	public void pojoSupplierFromType() {
+		Type type = ResolvableType.forClassWithGenerics(Supplier.class, Foo.class)
+				.getType();
+		FunctionType function = new FunctionType(type);
+		assertThat(function.getInputType()).isEqualTo(Void.class);
+		assertThat(function.getOutputType()).isEqualTo(Foo.class);
+		assertThat(function.getInputWrapper()).isEqualTo(Void.class);
+		assertThat(function.getOutputWrapper()).isEqualTo(Foo.class);
+		assertThat(function.isMessage()).isEqualTo(false);
+	}
+
 	@Test
 	public void plainFunctionFromApi() {
 		FunctionType function = FunctionType.from(Integer.class).to(String.class);

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

@@ -136,9 +136,9 @@ public class ContextFunctionCatalogAutoConfigurationTests {
 		assertThat(catalog.lookupFunction("names,foos")).isNull();
 		assertThat(inspector.getOutputType(catalog.lookupSupplier("names,foos")))
 				.isAssignableFrom(Foo.class);
-		// The input type is the same as the output type of the first element in the chain
+		// The input type is the same as the input type of the first element in the chain
 		assertThat(inspector.getInputType(catalog.lookupSupplier("names,foos")))
-				.isAssignableFrom(String.class);
+				.isAssignableFrom(Void.class);
 	}
 
 	@Test
@@ -148,9 +148,9 @@ public class ContextFunctionCatalogAutoConfigurationTests {
 		assertThat(catalog.lookupFunction("foos,print")).isNull();
 		assertThat(inspector.getInputType(catalog.lookupConsumer("foos,print")))
 				.isAssignableFrom(String.class);
-		// The output type is the same as the input type of the last element in the chain
+		// The output type is the same as the output type of the last element in the chain
 		assertThat(inspector.getOutputType(catalog.lookupConsumer("foos,print")))
-				.isAssignableFrom(Foo.class);
+				.isAssignableFrom(Void.class);
 	}
 
 	@Test
@@ -543,7 +543,8 @@ public class ContextFunctionCatalogAutoConfigurationTests {
 
 	@EnableAutoConfiguration
 	@Configuration
-	protected static class SingletonMessageConfiguration implements BeanFactoryPostProcessor {
+	protected static class SingletonMessageConfiguration
+			implements BeanFactoryPostProcessor {
 
 		@Override
 		public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory)
@@ -570,7 +571,8 @@ public class ContextFunctionCatalogAutoConfigurationTests {
 
 	}
 
-	protected static class SingletonMessageFunction implements Function<Message<Integer>, Message<String>> {
+	protected static class SingletonMessageFunction
+			implements Function<Message<Integer>, Message<String>> {
 
 		@Override
 		public Message<String> apply(Message<Integer> input) {
@@ -672,24 +674,28 @@ public class ContextFunctionCatalogAutoConfigurationTests {
 
 	@EnableAutoConfiguration
 	@Configuration
-	protected static class FactoryBeanConfiguration implements BeanDefinitionRegistryPostProcessor {
+	protected static class FactoryBeanConfiguration
+			implements BeanDefinitionRegistryPostProcessor {
 
 		@Override
-		public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException {
+		public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry)
-			RootBeanDefinition beanDefinition = new RootBeanDefinition(FunctionFactoryBean.class);
+				throws BeansException {
+			RootBeanDefinition beanDefinition = new RootBeanDefinition(
+					FunctionFactoryBean.class);
 			beanDefinition.setSource(new DescriptiveResource("Function"));
 			registry.registerBeanDefinition("function", beanDefinition);
 		}
 
 		@Override
-		public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
+		public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory)
+				throws BeansException {
 
 		}
 
 	}
 
-
+	private static class FunctionFactoryBean
-	private static class FunctionFactoryBean extends AbstractFactoryBean<Function<String, String>> {
+			extends AbstractFactoryBean<Function<String, String>> {
 
 		@Override
 		public Class<?> getObjectType() {

spring-cloud-function-web/src/main/java/org/springframework/cloud/function/web/flux/BetterGsonHttpMessageConverter.java

@@ -114,7 +114,6 @@ public class BetterGsonHttpMessageConverter
 	}
 
 	@Override
-	@SuppressWarnings("deprecation")
 	public Object read(Type type, Class<?> contextClass, HttpInputMessage inputMessage)
 			throws IOException, HttpMessageNotReadableException {
 
@@ -123,7 +122,6 @@ public class BetterGsonHttpMessageConverter
 	}
 
 	@Override
-	@SuppressWarnings("deprecation")
 	protected Object readInternal(Class<?> clazz, HttpInputMessage inputMessage)
 			throws IOException, HttpMessageNotReadableException {
 

spring-cloud-function-web/src/main/java/org/springframework/cloud/function/web/flux/response/FluxReturnValueHandler.java

@@ -165,7 +165,8 @@ public class FluxReturnValueHandler implements AsyncHandlerMethodReturnValueHand
 		}
 
 		MediaType mediaType = null;
-		if (isPlainText(webRequest) && CharSequence.class.isAssignableFrom(type)) {
+		if (isPlainText(webRequest) && (CharSequence.class.isAssignableFrom(type)
+				|| Void.class.isAssignableFrom(type))) {
 			mediaType = MediaType.TEXT_PLAIN;
 		}
 		else {