Polish PathVariableMapMethodArgumentResolver

Return an empty map when there are no path variables, rather than
raising an exception. This is consistent with similar resolvers for
extracting headers and request parameters.

Issue: SPR-9289

spring-webmvc/src/main/java/org/springframework/web/servlet/mvc/method/annotation/PathVariableMapMethodArgumentResolver.java

@@ -22,7 +22,6 @@ import java.util.Map;
 import org.springframework.core.MethodParameter;
 import org.springframework.util.CollectionUtils;
 import org.springframework.util.StringUtils;
-import org.springframework.web.bind.ServletRequestBindingException;
 import org.springframework.web.bind.annotation.PathVariable;
 import org.springframework.web.bind.support.WebDataBinderFactory;
 import org.springframework.web.context.request.NativeWebRequest;
@@ -31,6 +30,8 @@ import org.springframework.web.method.support.HandlerMethodArgumentResolver;
 import org.springframework.web.method.support.ModelAndViewContainer;
 import org.springframework.web.servlet.HandlerMapping;
 
+import edu.emory.mathcs.backport.java.util.Collections;
+
 /**
  * Resolves {@link Map} method arguments annotated with an @{@link PathVariable}
  * where the annotation does not specify a path variable name. The created
@@ -49,9 +50,7 @@ public class PathVariableMapMethodArgumentResolver implements HandlerMethodArgum
 	}
 
 	/**
-	 * Return a Map with all URI template variables.
-	 * @throws ServletRequestBindingException if no URI vars are found in the
-	 * 	request attribute {@link HandlerMapping#URI_TEMPLATE_VARIABLES_ATTRIBUTE}
+	 * Return a Map with all URI template variables or an empty map.
 	 */
 	public Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer,
 			NativeWebRequest webRequest, WebDataBinderFactory binderFactory) throws Exception {
@@ -61,12 +60,12 @@ public class PathVariableMapMethodArgumentResolver implements HandlerMethodArgum
 				(Map<String, String>) webRequest.getAttribute(
 						HandlerMapping.URI_TEMPLATE_VARIABLES_ATTRIBUTE, RequestAttributes.SCOPE_REQUEST);
 
-		if (CollectionUtils.isEmpty(uriTemplateVars)) {
-			throw new ServletRequestBindingException(
-					"No URI template variables for method parameter type [" + parameter.getParameterType() + "]");
+		if (!CollectionUtils.isEmpty(uriTemplateVars)) {
+			return new LinkedHashMap<String, String>(uriTemplateVars);
+		}
+		else {
+			return Collections.emptyMap();
 		}
-
-		return new LinkedHashMap<String, String>(uriTemplateVars);
 	}
 
 }

spring-webmvc/src/test/java/org/springframework/web/servlet/mvc/method/annotation/PathVariableMapMethodArgumentResolverTests.java

@@ -21,6 +21,7 @@ import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertTrue;
 
 import java.lang.reflect.Method;
+import java.util.Collections;
 import java.util.HashMap;
 import java.util.Map;
 
@@ -89,9 +90,12 @@ public class PathVariableMapMethodArgumentResolverTests {
 		assertEquals(uriTemplateVars, result);
 	}
 
-	@Test(expected=ServletRequestBindingException.class)
+	@Test
+	@SuppressWarnings("unchecked")
 	public void resolveArgumentNoUriVars() throws Exception {
-		resolver.resolveArgument(paramMap, mavContainer, webRequest, null);
+		Map<String, String> map = (Map<String, String>) resolver.resolveArgument(paramMap, mavContainer, webRequest, null);
+
+		assertEquals(Collections.emptyMap(), map);
 	}