GH-3954: Fix WebFlux XML config for ambiguity (#3973)

* GH-3954: Fix WebFlux XML config for ambiguity

Fixes #3954

When `web-client` attribute is provided for the WebFlux outbound components configuration via XML,
the `encoding-mode` is silently ignored

* Check for `encoding-mode` attribute presence in the `WebFluxOutboundChannelAdapterParser`
when `web-client` is provided and throw respective exception to reject such a config

**Cherry-pick to `5.5.x`**

* * Improve error messages in the `WebFluxOutboundChannelAdapterParser`

Author: artembilan

spring-integration-webflux/src/main/java/org/springframework/integration/webflux/config/WebFluxOutboundChannelAdapterParser.java

@@ -49,6 +49,11 @@ static BeanDefinitionBuilder buildWebFluxRequestExecutingMessageHandler(Element
 
 		String webClientRef = element.getAttribute("web-client");
 		if (StringUtils.hasText(webClientRef)) {
+			if (element.hasAttribute("encoding-mode")) {
+				parserContext.getReaderContext()
+						.error("The 'web-client' and 'encoding-mode' attributes are mutually exclusive.", element);
+			}
+
 			builder.getBeanDefinition()
 					.getConstructorArgumentValues()
 					.addIndexedArgumentValue(1, new RuntimeBeanReference(webClientRef));
@@ -65,8 +70,8 @@ static BeanDefinitionBuilder buildWebFluxRequestExecutingMessageHandler(Element
 
 		if (hasType && hasTypeExpression) {
 			parserContext.getReaderContext()
-					.error("The 'publisher-element-type' and 'publisher-element-type-expression' " +
-							"are mutually exclusive. You can only have one or the other", element);
+					.error("The 'publisher-element-type' and 'publisher-element-type-expression' attributes " +
+							"are mutually exclusive.", element);
 		}
 
 		if (hasType) {

spring-integration-webflux/src/test/java/org/springframework/integration/webflux/config/WebFluxOutboundGatewayParser-encoding-mode-fail.xml

@@ -0,0 +1,15 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<beans xmlns="http://www.springframework.org/schema/beans"
+	   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+	   xmlns:int-webflux="http://www.springframework.org/schema/integration/webflux"
+	   xsi:schemaLocation="http://www.springframework.org/schema/beans https://www.springframework.org/schema/beans/spring-beans.xsd
+		http://www.springframework.org/schema/integration/webflux https://www.springframework.org/schema/integration/webflux/spring-integration-webflux.xsd">
+
+	<bean id="webClient" class="org.springframework.web.reactive.function.client.WebClient"
+				factory-method="create"/>
+
+	<int-webflux:outbound-gateway url="/fake"
+							   web-client="webClient"
+							   encoding-mode="VALUES_ONLY"/>
+
+</beans>

spring-integration-webflux/src/test/java/org/springframework/integration/webflux/config/WebFluxOutboundGatewayParserTests-context.xml

@@ -25,6 +25,7 @@
 	<outbound-gateway id="reactiveFullConfig"
 					  url="http://localhost/test2"
 					  http-method="PUT"
+					  encoding-mode="NONE"
 					  request-channel="requests"
 					  reply-timeout="1234"
 					  extract-request-payload="false"

spring-integration-webflux/src/test/java/org/springframework/integration/webflux/config/WebFluxOutboundGatewayParserTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2017-2021 the original author or authors.
+ * Copyright 2017-2022 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.integration.webflux.config;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
 
 import java.nio.charset.StandardCharsets;
 import java.util.Map;
@@ -26,7 +27,9 @@
 import org.springframework.beans.DirectFieldAccessor;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.beans.factory.annotation.Qualifier;
+import org.springframework.beans.factory.parsing.BeanDefinitionParsingException;
 import org.springframework.context.ApplicationContext;
+import org.springframework.context.support.ClassPathXmlApplicationContext;
 import org.springframework.expression.Expression;
 import org.springframework.http.HttpMethod;
 import org.springframework.integration.endpoint.AbstractEndpoint;
@@ -37,6 +40,7 @@
 import org.springframework.util.ObjectUtils;
 import org.springframework.web.reactive.function.BodyExtractor;
 import org.springframework.web.reactive.function.client.WebClient;
+import org.springframework.web.util.DefaultUriBuilderFactory;
 
 /**
  * @author Artem Bilan
@@ -129,6 +133,17 @@ public void reactiveFullConfig() {
 				.isEqualTo("headers.elementType");
 		assertThat(handlerAccessor.getPropertyValue("extractResponseBody"))
 				.isEqualTo(false);
+		assertThat(handlerAccessor.getPropertyValue("webClient.uriBuilderFactory.encodingMode"))
+				.isEqualTo(DefaultUriBuilderFactory.EncodingMode.NONE);
+	}
+
+	@Test
+	void webClientAndEncodingModeExclusiveness() {
+		assertThatExceptionOfType(BeanDefinitionParsingException.class)
+				.isThrownBy(() ->
+						new ClassPathXmlApplicationContext("WebFluxOutboundGatewayParser-encoding-mode-fail.xml",
+						getClass()))
+				.withMessageContaining("The 'web-client' and 'encoding-mode' attributes are mutually exclusive");
 	}
 
 }