PayloadMethodArgumentResolver supports Optional

Closes gh-28945

Author: rstoyanchev

spring-messaging/src/main/java/org/springframework/messaging/handler/annotation/support/PayloadMethodArgumentResolver.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2021 the original author or authors.
+ * Copyright 2002-2023 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.
@@ -17,6 +17,7 @@
 package org.springframework.messaging.handler.annotation.support;
 
 import java.lang.annotation.Annotation;
+import java.util.Optional;
 
 import org.springframework.core.MethodParameter;
 import org.springframework.core.annotation.AnnotationUtils;
@@ -27,6 +28,7 @@
 import org.springframework.messaging.converter.SmartMessageConverter;
 import org.springframework.messaging.handler.annotation.Payload;
 import org.springframework.messaging.handler.invocation.HandlerMethodArgumentResolver;
+import org.springframework.messaging.support.MessageBuilder;
 import org.springframework.util.Assert;
 import org.springframework.util.ClassUtils;
 import org.springframework.util.ObjectUtils;
@@ -113,24 +115,30 @@ public Object resolveArgument(MethodParameter parameter, Message<?> message) thr
 			throw new IllegalStateException("@Payload SpEL expressions not supported by this resolver");
 		}
 
+		boolean isOptionalTargetClass = (parameter.getParameterType() == Optional.class);
 		Object payload = message.getPayload();
 		if (isEmptyPayload(payload)) {
-			if (ann == null || ann.required()) {
+			if ((ann == null || ann.required()) && !isOptionalTargetClass) {
 				String paramName = getParameterName(parameter);
 				BindingResult bindingResult = new BeanPropertyBindingResult(payload, paramName);
 				bindingResult.addError(new ObjectError(paramName, "Payload value must not be empty"));
 				throw new MethodArgumentNotValidException(message, parameter, bindingResult);
 			}
 			else {
-				return null;
+				return (isOptionalTargetClass ? Optional.empty() : null);
 			}
 		}
 
+		if (payload instanceof Optional<?> optional) {
+			payload = optional.get();
+			message = MessageBuilder.createMessage(payload, message.getHeaders());
+		}
+
 		Class<?> targetClass = resolveTargetClass(parameter, message);
 		Class<?> payloadClass = payload.getClass();
 		if (ClassUtils.isAssignable(targetClass, payloadClass)) {
 			validate(message, parameter, payload);
-			return payload;
+			return (isOptionalTargetClass ? Optional.of(payload) : payload);
 		}
 		else {
 			if (this.converter instanceof SmartMessageConverter smartConverter) {
@@ -144,7 +152,7 @@ public Object resolveArgument(MethodParameter parameter, Message<?> message) thr
 						payloadClass.getName() + "] to [" + targetClass.getName() + "] for " + message);
 			}
 			validate(message, parameter, payload);
-			return payload;
+			return (isOptionalTargetClass ? Optional.of(payload) : payload);
 		}
 	}
 
@@ -161,11 +169,14 @@ protected boolean isEmptyPayload(@Nullable Object payload) {
 		if (payload == null) {
 			return true;
 		}
-		else if (payload instanceof byte[]) {
-			return ((byte[]) payload).length == 0;
+		else if (payload instanceof byte[] bytes) {
+			return bytes.length == 0;
+		}
+		else if (payload instanceof String s) {
+			return !StringUtils.hasText(s);
 		}
-		else if (payload instanceof String) {
-			return !StringUtils.hasText((String) payload);
+		else if (payload instanceof Optional<?> optional) {
+			return optional.isEmpty();
 		}
 		else {
 			return false;
@@ -184,7 +195,7 @@ else if (payload instanceof String) {
 	 * @since 5.2
 	 */
 	protected Class<?> resolveTargetClass(MethodParameter parameter, Message<?> message) {
-		return parameter.getParameterType();
+		return parameter.nestedIfOptional().getNestedParameterType();
 	}
 
 	/**

spring-messaging/src/test/java/org/springframework/messaging/handler/annotation/support/PayloadMethodArgumentResolverTests.java

@@ -22,6 +22,7 @@
 import java.lang.annotation.Target;
 import java.lang.reflect.Method;
 import java.util.Locale;
+import java.util.Optional;
 
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
@@ -61,6 +62,8 @@ public class PayloadMethodArgumentResolverTests {
 
 	private MethodParameter paramWithSpelExpression;
 
+	private MethodParameter paramOptional;
+
 	private MethodParameter paramNotAnnotated;
 
 	private MethodParameter paramValidatedNotAnnotated;
@@ -74,16 +77,17 @@ public void setup() throws Exception {
 
 		Method payloadMethod = PayloadMethodArgumentResolverTests.class.getDeclaredMethod(
 				"handleMessage", String.class, String.class, Locale.class,
-				String.class, String.class, String.class, String.class);
+				String.class, Optional.class, String.class, String.class, String.class);
 
 		this.paramAnnotated = new SynthesizingMethodParameter(payloadMethod, 0);
 		this.paramAnnotatedNotRequired = new SynthesizingMethodParameter(payloadMethod, 1);
 		this.paramAnnotatedRequired = new SynthesizingMethodParameter(payloadMethod, 2);
 		this.paramWithSpelExpression = new SynthesizingMethodParameter(payloadMethod, 3);
-		this.paramValidated = new SynthesizingMethodParameter(payloadMethod, 4);
+		this.paramOptional = new SynthesizingMethodParameter(payloadMethod, 4);
+		this.paramValidated = new SynthesizingMethodParameter(payloadMethod, 5);
 		this.paramValidated.initParameterNameDiscovery(new DefaultParameterNameDiscoverer());
-		this.paramValidatedNotAnnotated = new SynthesizingMethodParameter(payloadMethod, 5);
-		this.paramNotAnnotated = new SynthesizingMethodParameter(payloadMethod, 6);
+		this.paramValidatedNotAnnotated = new SynthesizingMethodParameter(payloadMethod, 6);
+		this.paramNotAnnotated = new SynthesizingMethodParameter(payloadMethod, 7);
 	}
 
 	@Test
@@ -127,13 +131,33 @@ public void resolveNotRequired() throws Exception {
 		Message<?> emptyByteArrayMessage = MessageBuilder.withPayload(new byte[0]).build();
 		assertThat(this.resolver.resolveArgument(this.paramAnnotatedNotRequired, emptyByteArrayMessage)).isNull();
 
-		Message<?> emptyStringMessage = MessageBuilder.withPayload("").build();
+		Message<?> emptyStringMessage = MessageBuilder.withPayload(" 	").build();
 		assertThat(this.resolver.resolveArgument(this.paramAnnotatedNotRequired, emptyStringMessage)).isNull();
+		assertThat(((Optional<?>) this.resolver.resolveArgument(this.paramOptional, emptyStringMessage)).isEmpty()).isTrue();
+
+		Message<?> emptyOptionalMessage = MessageBuilder.withPayload(Optional.empty()).build();
+		assertThat(this.resolver.resolveArgument(this.paramAnnotatedNotRequired, emptyOptionalMessage)).isNull();
 
 		Message<?> notEmptyMessage = MessageBuilder.withPayload("ABC".getBytes()).build();
 		assertThat(this.resolver.resolveArgument(this.paramAnnotatedNotRequired, notEmptyMessage)).isEqualTo("ABC");
 	}
 
+	@Test
+	public void resolveOptionalTarget() throws Exception {
+		Message<?> message = MessageBuilder.withPayload("ABC".getBytes()).build();
+		Object actual = this.resolver.resolveArgument(paramOptional, message);
+
+		assertThat(((Optional<?>) actual).get()).isEqualTo("ABC");
+	}
+
+	@Test
+	public void resolveOptionalSource() throws Exception {
+		Message<?> message = MessageBuilder.withPayload(Optional.of("ABC".getBytes())).build();
+		Object actual = this.resolver.resolveArgument(paramAnnotated, message);
+
+		assertThat(actual).isEqualTo("ABC");
+	}
+
 	@Test
 	public void resolveNonConvertibleParam() {
 		Message<?> notEmptyMessage = MessageBuilder.withPayload(123).build();
@@ -218,6 +242,7 @@ private void handleMessage(
 			@Payload(required=false) String paramNotRequired,
 			@Payload(required=true) Locale nonConvertibleRequiredParam,
 			@Payload("foo.bar") String paramWithSpelExpression,
+			@Payload Optional<String> optionalParam,
 			@MyValid @Payload String validParam,
 			@Validated String validParamNotAnnotated,
 			String paramNotAnnotated) {