#342 - Augment error message when building link without a web request.

We now explicitly check whether we could look up request attributes and throw an exception with a message indicating the cause of the failure.

Original pull request: #344.

src/main/java/org/springframework/hateoas/mvc/ControllerLinkBuilder.java

@@ -17,11 +17,10 @@ package org.springframework.hateoas.mvc;
 
 import static org.springframework.util.StringUtils.*;
 
+import javax.servlet.http.HttpServletRequest;
 import java.lang.reflect.Method;
 import java.net.URI;
 
-import javax.servlet.http.HttpServletRequest;
-
 import org.springframework.hateoas.Link;
 import org.springframework.hateoas.core.AnnotationMappingDiscoverer;
 import org.springframework.hateoas.core.DummyInvocationUtils;
@@ -237,7 +236,7 @@ public class ControllerLinkBuilder extends LinkBuilderSupport<ControllerLinkBuil
 	private static HttpServletRequest getCurrentRequest() {
 
 		RequestAttributes requestAttributes = RequestContextHolder.getRequestAttributes();
-		Assert.state(requestAttributes != null, "Could not find current request via RequestContextHolder");
+		Assert.state(requestAttributes != null, "Could not find current request via RequestContextHolder. Is this being called from a Spring MVC handler?");
 		Assert.isInstanceOf(ServletRequestAttributes.class, requestAttributes);
 		HttpServletRequest servletRequest = ((ServletRequestAttributes) requestAttributes).getRequest();
 		Assert.state(servletRequest != null, "Could not find current HttpServletRequest");

src/test/java/org/springframework/hateoas/mvc/ControllerLinkBuilderOutsideSpringMvcUnitTest.java

@@ -0,0 +1,41 @@
+package org.springframework.hateoas.mvc;
+
+import static org.hamcrest.MatcherAssert.*;
+import static org.hamcrest.Matchers.*;
+import static org.springframework.hateoas.mvc.ControllerLinkBuilder.*;
+
+import org.junit.Before;
+import org.junit.Test;
+import org.springframework.web.context.request.RequestContextHolder;
+
+/**
+ * Test cases for {@link ControllerLinkBuilder} that are NOT inside an existing Spring MVC request
+ *
+ * @author Greg Turnquist
+ */
+public class ControllerLinkBuilderOutsideSpringMvcUnitTest {
+
+	/**
+	 * Clear out any existing request attributes left behind by other tests
+	 */
+	@Before
+	public void setUp() {
+		RequestContextHolder.setRequestAttributes(null);
+	}
+
+	/**
+	 * @see #342
+	 */
+	@Test(expected = IllegalStateException.class)
+	public void createsLinkToMethodOnParameterizedControllerRoot() {
+
+		try {
+			linkTo(methodOn(ControllerLinkBuilderUnitTest.PersonsAddressesController.class, 15)
+					.getAddressesForCountry("DE")).withSelfRel();
+		} catch (IllegalStateException e) {
+			assertThat(e.getMessage(), equalTo("Could not find current request via RequestContextHolder. Is this being called from a Spring MVC handler?"));
+			throw e;
+		}
+	}
+
+}