Align UriComponents.toUri() with toUriString()

Update HierarchicalUriComponents.toUri() to only prepend a missing '/'
when the scheme, user info, host or port are specified. This makes
the toUri() method behave in the same way as .toUriString() and allows
relative URIs to be created.

Issue: SPR-10231

spring-web/src/main/java/org/springframework/web/util/HierarchicalUriComponents.java

@@ -407,8 +407,11 @@ final class HierarchicalUriComponents extends UriComponents {
 			else {
 				String path = getPath();
 				if (StringUtils.hasLength(path) && path.charAt(0) != PATH_DELIMITER) {
+					// Only prefix the path delimiter if something exists before it
+					if(getScheme() != null || getUserInfo() != null || getHost() != null || getPort() != -1) {
 						path = PATH_DELIMITER + path;
 					}
+				}
 				return new URI(getScheme(), getUserInfo(), getHost(), getPort(), path, getQuery(),
 						getFragment());
 			}

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

@@ -57,7 +57,9 @@ public class UriComponentsBuilderTests {
 		assertEquals("bar", result.getQuery());
 		assertEquals("baz", result.getFragment());
 
-		URI expected = new URI("/foo?bar#baz");
+		assertEquals("Invalid result URI String", "foo?bar#baz", result.toUriString());
+
+		URI expected = new URI("foo?bar#baz");
 		assertEquals("Invalid result URI", expected, result.toUri());
 
 		result = UriComponentsBuilder.fromPath("/foo").build();
@@ -332,4 +334,16 @@ public class UriComponentsBuilderTests {
 		assertThat(uriComponents.toUriString(), equalTo("http://example.com/foo?bar"));
 	}
 
+	@Test
+	public void relativeUrls() throws Exception {
+		assertThat(UriComponentsBuilder.fromUriString("http://example.com/foo/../bar").build().toString(), equalTo("http://example.com/foo/../bar"));
+		assertThat(UriComponentsBuilder.fromUriString("http://example.com/foo/../bar").build().toUriString(), equalTo("http://example.com/foo/../bar"));
+		assertThat(UriComponentsBuilder.fromUriString("http://example.com/foo/../bar").build().toUri().getPath(), equalTo("/foo/../bar"));
+		assertThat(UriComponentsBuilder.fromUriString("../../").build().toString(), equalTo("../../"));
+		assertThat(UriComponentsBuilder.fromUriString("../../").build().toUriString(), equalTo("../../"));
+		assertThat(UriComponentsBuilder.fromUriString("../../").build().toUri().getPath(), equalTo("../../"));
+		assertThat(UriComponentsBuilder.fromUriString("http://example.com").path("foo/../bar").build().toString(), equalTo("http://example.com/foo/../bar"));
+		assertThat(UriComponentsBuilder.fromUriString("http://example.com").path("foo/../bar").build().toUriString(), equalTo("http://example.com/foo/../bar"));
+		assertThat(UriComponentsBuilder.fromUriString("http://example.com").path("foo/../bar").build().toUri().getPath(), equalTo("/foo/../bar"));
+	}
 }