Restore log level for resolved exceptions

The fix for SPR-17178 switched from debug to warn level warning for
all sub-classes of AbstractHandlerExceptionResolver where the request
concerned the DefaultHandlerExceptionResolver only.

This commit restores the original DEBUG level logging that was in
AbstractHandlerExceptionResolver from before SPR-17178. In addition
DefaultHandlerExceptionResolver registers a warnLogCategory by default
which enables warn logging and hence fulfilling the original goal
for SPR-17178.

Issue: SPR-17383

spring-webmvc/src/main/java/org/springframework/web/servlet/handler/AbstractHandlerExceptionResolver.java

@@ -136,8 +136,8 @@ public abstract class AbstractHandlerExceptionResolver implements HandlerExcepti
 			ModelAndView result = doResolveException(request, response, handler, ex);
 			if (result != null) {
 				// Print warn message when warn logger is not enabled...
-				if (logger.isWarnEnabled() && (this.warnLogger == null || !this.warnLogger.isWarnEnabled())) {
-					logger.warn("Resolved [" + ex + "]" + (result.isEmpty() ? "" : " to " + result));
+				if (logger.isDebugEnabled() && (this.warnLogger == null || !this.warnLogger.isWarnEnabled())) {
+					logger.debug("Resolved [" + ex + "]" + (result.isEmpty() ? "" : " to " + result));
 				}
 				// warnLogger with full stack trace (requires explicit config)
 				logException(ex, request);

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

@@ -159,6 +159,7 @@ public class DefaultHandlerExceptionResolver extends AbstractHandlerExceptionRes
 	 */
 	public DefaultHandlerExceptionResolver() {
 		setOrder(Ordered.LOWEST_PRECEDENCE);
+		setWarnLogCategory(getClass().getName());
 	}