#475 - Support all variable formats.

RFC-6570 specifies percent-encoding as a valid way to encode characters. By expanding the regex for UriTemplate to include '%', it's possible to support all variants.

See: https://tools.ietf.org/html/rfc6570#section-2.3

Original issue: #246

src/main/java/org/springframework/hateoas/UriTemplate.java

@@ -51,7 +51,7 @@ import org.springframework.web.util.UriUtils;
  */
 public class UriTemplate implements Iterable<TemplateVariable>, Serializable {
 
-	private static final Pattern VARIABLE_REGEX = Pattern.compile("\\{([\\?\\&#/]?)([\\w\\,*]+)\\}");
+	private static final Pattern VARIABLE_REGEX = Pattern.compile("\\{([\\?\\&#/]?)([\\w%\\,*]+)\\}");
 	private static final long serialVersionUID = -1007874653930162262L;
 
 	private final TemplateVariables variables;

src/test/java/org/springframework/hateoas/UriTemplateUnitTest.java

@@ -39,7 +39,7 @@ import org.apache.commons.io.output.ByteArrayOutputStream;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.MethodSource;
-import org.springframework.hateoas.TemplateVariable.VariableType;
+import org.springframework.hateoas.TemplateVariable.*;
 
 /**
  * Unit tests for {@link UriTemplate}.
@@ -348,6 +348,20 @@ class UriTemplateUnitTest {
 		assertThat(UriTemplate.isTemplate("http://localhost/api/rest/v1/userGroups/50/functions/{?id*}")).isTrue();
 	}
 
+	@Test // #475
+	void variablesWithPercentEncodingShouldWork() {
+
+		assertThat(UriTemplate.of("http://localhost/foo/bar/{%24filter}").expand("value"))
+				.isEqualTo(URI.create("http://localhost/foo/bar/value"));
+	}
+
+	@Test // #475
+	void variablesWithUnderscoresShouldWork() {
+
+		assertThat(UriTemplate.of("http://localhost/foo/bar/{_filter}").expand("value"))
+				.isEqualTo(URI.create("http://localhost/foo/bar/value"));
+	}
+
 	private static void assertVariables(UriTemplate template, TemplateVariable... variables) {
 		assertVariables(template, Arrays.asList(variables));
 	}