Ensure classpath checks can be evaluated at build-time

Closes gh-29352

spring-messaging/src/main/java/org/springframework/messaging/converter/ProtobufMessageConverter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2020 the original author or authors.
+ * Copyright 2002-2022 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.
@@ -67,9 +67,12 @@ public class ProtobufMessageConverter extends AbstractMessageConverter {
 	 */
 	public static final MimeType PROTOBUF = new MimeType("application", "x-protobuf", DEFAULT_CHARSET);
 
+	private static final boolean protobufJsonFormatPresent =
+			ClassUtils.isPresent("com.google.protobuf.util.JsonFormat", ProtobufMessageConverter.class.getClassLoader());
 
 	private static final Map<Class<?>, Method> methodCache = new ConcurrentReferenceHashMap<>();
 
+
 	final ExtensionRegistry extensionRegistry;
 
 	@Nullable
@@ -98,7 +101,7 @@ public class ProtobufMessageConverter extends AbstractMessageConverter {
 		if (formatSupport != null) {
 			this.protobufFormatSupport = formatSupport;
 		}
-		else if (ClassUtils.isPresent("com.google.protobuf.util.JsonFormat", getClass().getClassLoader())) {
+		else if (protobufJsonFormatPresent) {
 			this.protobufFormatSupport = new ProtobufJavaUtilSupport(null, null);
 		}
 		else {

spring-web/src/main/java/org/springframework/http/converter/protobuf/ProtobufHttpMessageConverter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2021 the original author or authors.
+ * Copyright 2002-2022 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.
@@ -105,9 +105,19 @@ public class ProtobufHttpMessageConverter extends AbstractHttpMessageConverter<M
 	 */
 	public static final String X_PROTOBUF_MESSAGE_HEADER = "X-Protobuf-Message";
 
+	private static final boolean protobufFormatFactoryPresent;
+
+	private static final boolean protobufJsonFormatPresent;
 
 	private static final Map<Class<?>, Method> methodCache = new ConcurrentReferenceHashMap<>();
 
+	static {
+		ClassLoader classLoader = ProtobufHttpMessageConverter.class.getClassLoader();
+		protobufFormatFactoryPresent = ClassUtils.isPresent("com.googlecode.protobuf.format.FormatFactory", classLoader);
+		protobufJsonFormatPresent = ClassUtils.isPresent("com.google.protobuf.util.JsonFormat", classLoader);
+	}
+
+
 	final ExtensionRegistry extensionRegistry;
 
 	@Nullable
@@ -136,10 +146,10 @@ public class ProtobufHttpMessageConverter extends AbstractHttpMessageConverter<M
 		if (formatSupport != null) {
 			this.protobufFormatSupport = formatSupport;
 		}
-		else if (ClassUtils.isPresent("com.googlecode.protobuf.format.FormatFactory", getClass().getClassLoader())) {
+		else if (protobufFormatFactoryPresent) {
 			this.protobufFormatSupport = new ProtobufJavaFormatSupport();
 		}
-		else if (ClassUtils.isPresent("com.google.protobuf.util.JsonFormat", getClass().getClassLoader())) {
+		else if (protobufJsonFormatPresent) {
 			this.protobufFormatSupport = new ProtobufJavaUtilSupport(null, null);
 		}
 		else {

spring-webflux/src/main/java/org/springframework/web/reactive/config/WebFluxConfigurationSupport.java

@@ -85,6 +85,10 @@ import org.springframework.web.server.i18n.LocaleContextResolver;
  */
 public class WebFluxConfigurationSupport implements ApplicationContextAware {
 
+	private static final boolean jakartaValidatorPresent =
+			ClassUtils.isPresent("jakarta.validation.Validator", WebFluxConfigurationSupport.class.getClassLoader());
+
+
 	@Nullable
 	private Map<String, CorsConfiguration> corsConfigurations;
 
@@ -384,7 +388,7 @@ public class WebFluxConfigurationSupport implements ApplicationContextAware {
 	public Validator webFluxValidator() {
 		Validator validator = getValidator();
 		if (validator == null) {
-			if (ClassUtils.isPresent("jakarta.validation.Validator", getClass().getClassLoader())) {
+			if (jakartaValidatorPresent) {
 				try {
 					validator = new OptionalValidatorFactoryBean();
 				}

spring-websocket/src/main/java/org/springframework/web/socket/config/WebSocketNamespaceHandler.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2013 the original author or authors.
+ * Copyright 2002-2022 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.
@@ -28,7 +28,7 @@ import org.springframework.util.ClassUtils;
  */
 public class WebSocketNamespaceHandler extends NamespaceHandlerSupport {
 
-	private static boolean isSpringMessagingPresent = ClassUtils.isPresent(
+	private static final boolean isSpringMessagingPresent = ClassUtils.isPresent(
 			"org.springframework.messaging.Message", WebSocketNamespaceHandler.class.getClassLoader());