private static final Set<String> RESERVED_NAMES = Set.of(
 "CON", "PRN", "AUX", "NUL", "COM1", "COM2", "COM3", "COM4", "COM5", "COM6",
 "COM7", "COM8", "COM9", "LPT1", "LPT2", "LPT3", "LPT4", "LPT5", "LPT6",
 "LPT7", "LPT8", "LPT9"
);
public static void validateSafePathComponent(String component) {
 // --- 1. Basic Checks (Using Apache Commons Lang) ---
 Validate.notBlank(component, "Path component must not be blank");
 Validate.isTrue(component.length() <= 255, "Path component too long");
 // Pre-decode raw dangerous percent encodings
 String lower = component.toLowerCase(Locale.ROOT);
 if (lower.contains("%2f") || lower.contains("%5c") || lower.contains("%00")) {
 throw new IllegalArgumentException("Encoded separator/null not allowed: " + component);
 }
 // --- 2. Decoding ---
 String decoded;
 try {
 decoded = URLDecoder.decode(component, StandardCharsets.UTF_8);
 } catch (IllegalArgumentException ex) {
 throw new IllegalArgumentException("Invalid percent encoding: " + component);
 }
 // --- 3. Path Traversal/Normalization Check (Using Path API) ---
 Path p;
 try {
 p = Path.of(decoded);
 } catch (InvalidPathException e) {
 throw new IllegalArgumentException("Invalid path syntax: " + component);
 }
 // Critical Path Traversal check: must be a single name and not contain '..' or '.'
 if (p.isAbsolute() || p.getNameCount() != 1 || !p.normalize().equals(p)) {
 throw new IllegalArgumentException("Traversal/dot segments or absolute path not allowed: " + component);
 }
 String name = p.getFileName().toString();
 // --- 4. Final Name/Custom Policy Checks ---
 // Basic character / separator checks
 if (name.contains("/") || name.contains("\\") || name.indexOf('0円') >= 0 || name.contains("+")) {
 throw new IllegalArgumentException("Unsafe characters (separators/null/plus): " + component);
 }
 // Control chars
 for (int i = 0; i < name.length(); i++) {
 char c = name.charAt(i);
 if (c < 0x20 || c == 0x7F) {
 throw new IllegalArgumentException("Control character present: " + component);
 }
 }
 // Dot-only or reserved dot forms & Trailing space/dot
 if (name.equals(".") || name.equals("..") || name.matches("\\.{2,}") ||
 name.endsWith(" ") || name.endsWith(".")) {
 throw new IllegalArgumentException("Invalid dot sequence or trailing space/dot: " + component);
 }
 // Allowlist
 if (!name.matches("[A-Za-z0-9._-]+")) {
 throw new IllegalArgumentException("Disallowed characters: " + component);
 }
 // Windows reserved device names
 if (RESERVED_NAMES.contains(name.toUpperCase(Locale.ROOT))) {
 throw new IllegalArgumentException("Reserved device name: " + component);
 }
}