Add logging and compacting on unexpected exception during filtering

logbook-json/src/main/java/org/zalando/logbook/json/JacksonJsonFieldBodyFilter.java

@@ -12,14 +12,22 @@
 import com.fasterxml.jackson.core.JsonToken;
 import com.fasterxml.jackson.databind.ObjectMapper;
 
+import lombok.extern.slf4j.Slf4j;
+
 /**
  * 
- * Thread-safe filter for JSON fields. Filters on property names, 
+ * Thread-safe filter for JSON fields. Filters on property names.
+ * <br><br> 
+ * Output is always compacted, even in case of invalid JSON, 
+ * so this filter should not be used in conjunction with {@linkplain JsonCompactor}.
  *
  */
 
+@Slf4j
 public class JacksonJsonFieldBodyFilter implements BodyFilter {
 
+    private final static StringReplaceJsonCompactor fallbackCompactor = new StringReplaceJsonCompactor();
+
     private final String replacement;
     private final Set<String> fields;
     private final ObjectMapper objectMapper;
@@ -71,10 +79,9 @@ public String filter(final String body) {
 
             return writer.toString();
         } catch(Exception e) {
-            // ignore
+            log.trace("Unable to filter body, is it a JSON?. Keep as-is. `{}`", e.getMessage()); 
+            return fallbackCompactor.compact(body);
         }
-        return body;
-}
-
+    }
 
 }