Fix regression with opaque URI determination

Before RfcUriParser we expected opaque URI's to not have ":/"
after the scheme while the new parser expect opaque URI's to
not have a slash anywhere after the scheme. This commit
restores the previous behavior.

Closes gh-34588

Author: rstoyanchev

Diff for: spring-web/src/main/java/org/springframework/web/util/RfcUriParser.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2024 the original author or authors.
+ * Copyright 2002-2025 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.
@@ -503,8 +503,7 @@ public void index(int index) {
 		// Component capture
 
 		public InternalParser resolveIfOpaque() {
-			boolean hasSlash = (this.uri.indexOf('/', this.index + 1) == -1);
-			this.isOpaque = (hasSlash && !hierarchicalSchemes.contains(this.scheme));
+			this.isOpaque = (this.uri.charAt(this.index) != '/' && !hierarchicalSchemes.contains(this.scheme));
 			return this;
 		}
 

Diff for: spring-web/src/test/java/org/springframework/web/util/UriComponentsBuilderTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2024 the original author or authors.
+ * Copyright 2002-2025 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.
@@ -155,6 +155,19 @@ void fromOpaqueUri() {
 		assertThat(result.toUri()).as("Invalid result URI").isEqualTo(uri);
 	}
 
+	@ParameterizedTest // see gh-34588
+	@EnumSource
+	void fromOpaqueUriWithUrnScheme(ParserType parserType) {
+		URI uri = UriComponentsBuilder
+				.fromUriString("urn:text:service-{region}:{prefix}/{id}", parserType).build()
+				.expand("US", "prefix1", "Id-2")
+				.toUri();
+
+		assertThat(uri.getScheme()).isEqualTo("urn");
+		assertThat(uri.isOpaque()).isTrue();
+		assertThat(uri.getSchemeSpecificPart()).isEqualTo("text:service-US:prefix1/Id-2");
+	}
+
 	@ParameterizedTest // see gh-9317
 	@EnumSource
 	void fromUriEncodedQuery(ParserType parserType) {