Task5.java

import java.util.List;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

class DocumentValidator {

    private static final Logger log = LoggerFactory.getLogger(DocumentValidator.class);

    public ValidationResult validate(Document doc) {
        try {
            if (doc == null) {
                // FIX: Treat null document as an expected validation failure instead of throwing RuntimeException.
                log.warn("Validation failed: document is null");
                return ValidationResult.invalid("Document is null");
            }

            String content = doc.extractContent();
            if (content == null || content.isEmpty()) {
                // FIX: Return a validation failure result for empty content instead of flooding logs with stack traces.
                log.warn("Validation failed: empty content");
                return ValidationResult.invalid("Empty content");
            }
            return runValidationRules(content);

        } catch (IllegalArgumentException e) {
            // FIX: Expected rule-level validation failure is logged without stack trace and returned as invalid result.
            log.warn("Validation failed: {}", e.getMessage());
            return ValidationResult.invalid(e.getMessage());
        } catch (Exception e) {
            // FIX: Replace printStackTrace() and null return with structured SLF4J logging plus exception propagation.
            log.error("Unexpected error while validating document", e);
            throw new IllegalStateException("Unexpected error while validating document", e);
        }
    }

    public void validateBatch(List<Document> docs) {
        for (Document doc : docs) {
            try {
                ValidationResult r = validate(doc);
                // FIX: Guard against null ValidationResult before calling isValid() to avoid NullPointerException.
                if (r != null && r.isValid()) {
                    saveResult(r);
                }
            } catch (Exception e) {
                // FIX: Do not silently swallow batch exceptions; log them with context for production support analysis.
                log.error("Document validation failed during batch processing", e);
            }
        }
    }

    private ValidationResult runValidationRules(String content) {
        // Existing validation rule logic remains unchanged.
        return ValidationResult.valid();
    }

    private void saveResult(ValidationResult result) {
        // Existing persistence logic remains unchanged.
    }
}