Reduce warn logs noise

dspace-server-webapp/src/main/java/org/dspace/app/rest/exception/DSpaceApiExceptionControllerAdvice.java

@@ -61,6 +61,13 @@
 public class DSpaceApiExceptionControllerAdvice extends ResponseEntityExceptionHandler {
     private static final Logger log = LogManager.getLogger();
 
+    /**
+     * Dedicated logger for 404 NOT_FOUND responses. Configured at OFF level by default
+     * so that expected 404s don't flood production logs.
+     * Set to WARN in log4j2.xml to see 404 responses in logs.
+     */
+    private static final Logger notFoundLog = LogManager.getLogger("org.dspace.app.rest.exception.DSpaceApiExceptionControllerAdvice.NotFound");
+
     /**
      * Default collection of HTTP error codes to log as ERROR with full stack trace.
      */
@@ -283,11 +290,9 @@ private void sendErrorResponseFromException(final HttpServletRequest request,
         if (statusCodesLoggedAsErrors.contains(statusCode)) {
             log.error("{} (status:{})", message, statusCode, ex);
         } else {
-            // Log the error as a single-line WARN
             StackTraceElement[] trace = ex.getStackTrace();
             String location = trace.length <= 0 ? "unknown" : trace[0].toString();
-            log.warn("{} (status:{} exception: {} at: {})",
-                    message, statusCode, ex.getClass().getName(), location);
+            logClientError(statusCode, message, ex.getClass().getName(), location);
         }
 
         response.sendError(statusCode, message);
@@ -322,7 +327,6 @@ private void sendErrorResponse(final HttpServletRequest request,
             // Log the full error and status code
             log.error("{} (status:{})", message, statusCode, ex);
         } else if (HttpStatus.valueOf(statusCode).is4xxClientError()) {
-            // Log the error as a single-line WARN
             String location;
             String exceptionMessage;
             if (null == ex) {
@@ -333,14 +337,28 @@ private void sendErrorResponse(final HttpServletRequest request,
                 StackTraceElement[] trace = ex.getStackTrace();
                 location = trace.length <= 0 ? "unknown" : trace[0].toString();
             }
-            log.warn("{} (status:{} exception: {} at: {})", message, statusCode,
-                    exceptionMessage, location);
+            logClientError(statusCode, message, exceptionMessage, location);
         }
 
         //Exception properties will be set by org.springframework.boot.web.support.ErrorPageFilter
         response.sendError(statusCode, message);
     }
 
+    /**
+     * Log a 4xx client error. 404 NOT_FOUND is sent to a dedicated logger ({@link #notFoundLog})
+     * at WARN level, but the logger is set to OFF by default in log4j2.xml (suppressed).
+     * Set logger to WARN in log4j2.xml to see 404 responses in logs.
+     */
+    private void logClientError(int statusCode, String message, String exceptionMessage, String location) {
+        if (statusCode == HttpServletResponse.SC_NOT_FOUND) {
+            notFoundLog.warn("{} (status:{} exception: {} at: {})", message, statusCode,
+                    exceptionMessage, location);
+        } else {
+            log.warn("{} (status:{} exception: {} at: {})", message, statusCode,
+                    exceptionMessage, location);
+        }
+    }
+
     /**
      * Get set of status codes that should be treated as errors.
      *
@@ -355,7 +373,6 @@ private Set<Integer> getStatusCodesLoggedAsErrors() {
                 statusCodesLoggedAsErrors.add(Integer.valueOf(code));
             } catch (NumberFormatException e) {
                 log.warn("Non-integer HTTP status code {} in {}", code, P_LOG_AS_ERROR);
-                // And continue
             }
         }
         return statusCodesLoggedAsErrors;

dspace/config/log4j2.xml

@@ -89,6 +89,13 @@
             <AppenderRef ref="A4" level="WARN"/>
         </Logger>
 
+        <!-- 404 NOT_FOUND responses. Set to WARN to see 404s in logs. -->
+        <Logger name='org.dspace.app.rest.exception.DSpaceApiExceptionControllerAdvice.NotFound'
+                level='OFF'
+                additivity='false'>
+            <AppenderRef ref='A1'/>
+        </Logger>
+
         <!-- The file downloads -->
         <Logger name="org.dspace.app.statistics.clarin.ClarinMatomoBitstreamTracker"
                 level="INFO"