GH-830 Fix conversioin exception for custom converters

Resolves #830

Author: olegz

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

@@ -18,7 +18,6 @@
 
 import java.lang.reflect.Type;
 import java.nio.charset.StandardCharsets;
-import java.util.Collection;
 
 import org.springframework.cloud.function.cloudevent.CloudEventMessageUtils;
 import org.springframework.cloud.function.json.JsonMapper;
@@ -76,9 +75,6 @@ protected boolean canConvertFrom(Message<?> message, @Nullable Class<?> targetCl
 
 	@Override
 	protected Object convertFromInternal(Message<?> message, Class<?> targetClass, @Nullable Object conversionHint) {
-		if (targetClass.isInstance(message.getPayload()) && !(message.getPayload() instanceof Collection<?>)) {
-			return message.getPayload();
-		}
 		Type convertToType = conversionHint == null ? targetClass : (Type) conversionHint;
 		if (targetClass == byte[].class && message.getPayload() instanceof String) {
 			return ((String) message.getPayload()).getBytes(StandardCharsets.UTF_8);

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

@@ -45,6 +45,9 @@ public SmartCompositeMessageConverter(Collection<MessageConverter> converters) {
 	@Nullable
 	public Object fromMessage(Message<?> message, Class<?> targetClass) {
 		for (MessageConverter converter : getConverters()) {
+			if (targetClass.isInstance(message.getPayload()) && !(message.getPayload() instanceof Collection<?>)) {
+				return message.getPayload();
+			}
 			Object result = converter.fromMessage(message, targetClass);
 			if (result != null) {
 				return result;
@@ -57,6 +60,9 @@ public Object fromMessage(Message<?> message, Class<?> targetClass) {
 	@Nullable
 	public Object fromMessage(Message<?> message, Class<?> targetClass, @Nullable Object conversionHint) {
 		for (MessageConverter converter : getConverters()) {
+			if (targetClass.isInstance(message.getPayload()) && !(message.getPayload() instanceof Collection<?>)) {
+				return message.getPayload();
+			}
 			Object result = (converter instanceof SmartMessageConverter ?
 					((SmartMessageConverter) converter).fromMessage(message, targetClass, conversionHint) :
 					converter.fromMessage(message, targetClass));

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

@@ -48,6 +48,7 @@
 import org.springframework.cloud.function.context.HybridFunctionalRegistrationTests.UppercaseFunction;
 import org.springframework.cloud.function.context.catalog.SimpleFunctionRegistry.FunctionInvocationWrapper;
 import org.springframework.cloud.function.context.config.JsonMessageConverter;
+import org.springframework.cloud.function.context.config.SmartCompositeMessageConverter;
 import org.springframework.cloud.function.json.GsonMapper;
 import org.springframework.cloud.function.json.JacksonMapper;
 import org.springframework.cloud.function.json.JsonMapper;
@@ -86,7 +87,7 @@ public void before() {
 		messageConverters.add(new JsonMessageConverter(jsonMapper));
 		messageConverters.add(new ByteArrayMessageConverter());
 		messageConverters.add(new StringMessageConverter());
-		this.messageConverter = new CompositeMessageConverter(messageConverters);
+		this.messageConverter = new SmartCompositeMessageConverter(messageConverters);
 
 		this.conversionService = new DefaultConversionService();
 	}