Add error message for missing servlet request param.

The DefaultHandlerExceptionResolver now provides an error message in
addition to setting the status of the response.

Issue: SPR-9312

spring-web/src/main/java/org/springframework/web/multipart/support/MissingServletRequestPartException.java

@@ -22,13 +22,13 @@ import org.springframework.web.multipart.MultipartResolver;
 
 /**
  * Raised when the part of a "multipart/form-data" request identified by its
- * name cannot be found. 
+ * name cannot be found.
- * 
+ *
- * <p>This may be because the request is not a multipart/form-data  
+ * <p>This may be because the request is not a multipart/form-data
- * 
+ *
- * either because the part is not present in the request, or 
+ * either because the part is not present in the request, or
- * because the web application is not configured correctly for processing 
+ * because the web application is not configured correctly for processing
- * multipart requests -- e.g. no {@link MultipartResolver}.  
+ * multipart requests -- e.g. no {@link MultipartResolver}.
  *
  * @author Rossen Stoyanchev
  * @since 3.1
@@ -40,7 +40,7 @@ public class MissingServletRequestPartException extends ServletException {
 	private final String partName;
 
 	public MissingServletRequestPartException(String partName) {
-		super("Request part '" + partName + "' not found.");
+		super("Required request part '" + partName + "' is not present.");
 		this.partName = partName;
 	}
 

spring-webmvc/src/main/java/org/springframework/web/servlet/mvc/support/DefaultHandlerExceptionResolver.java

@@ -258,7 +258,7 @@ public class DefaultHandlerExceptionResolver extends AbstractHandlerExceptionRes
 	protected ModelAndView handleMissingServletRequestParameter(MissingServletRequestParameterException ex,
 			HttpServletRequest request, HttpServletResponse response, Object handler) throws IOException {
 
-		response.sendError(HttpServletResponse.SC_BAD_REQUEST);
+		response.sendError(HttpServletResponse.SC_BAD_REQUEST, ex.getMessage());
 		return new ModelAndView();
 	}
 
@@ -384,7 +384,7 @@ public class DefaultHandlerExceptionResolver extends AbstractHandlerExceptionRes
 	 */
 	protected ModelAndView handleMissingServletRequestPartException(MissingServletRequestPartException ex,
 			HttpServletRequest request, HttpServletResponse response, Object handler) throws IOException {
- 		response.sendError(HttpServletResponse.SC_BAD_REQUEST);
+		response.sendError(HttpServletResponse.SC_BAD_REQUEST, ex.getMessage());
 		return new ModelAndView();
 	}
 

spring-webmvc/src/test/java/org/springframework/web/servlet/mvc/support/DefaultHandlerExceptionResolverTests.java

@@ -98,6 +98,7 @@ public class DefaultHandlerExceptionResolverTests {
 		assertNotNull("No ModelAndView returned", mav);
 		assertTrue("No Empty ModelAndView returned", mav.isEmpty());
 		assertEquals("Invalid status code", 400, response.getStatus());
+		assertEquals("Required bar parameter 'foo' is not present", response.getErrorMessage());
 	}
 
 	@Test
@@ -156,6 +157,7 @@ public class DefaultHandlerExceptionResolverTests {
 		assertNotNull("No ModelAndView returned", mav);
 		assertTrue("No Empty ModelAndView returned", mav.isEmpty());
 		assertEquals("Invalid status code", 400, response.getStatus());
+		assertEquals("Required request part 'name' is not present.", response.getErrorMessage());
 	}
 
 	@Test