Strategi Pengesahan Input Menyeluruh

public class InputValidator {
  public static boolean isValidUsername(String username) {
    if (username == null || username.isEmpty()) {
      return false;
    }
    // Whitelist: only letters, numbers, and underscore
    return username.matches("^[a-zA-Z0-9_]+$");
  }

  public static void main(String[] args) {
    String user1 = "coddy_kit_123";
    String user2 = "bad user!";
    String user3 = "admin";

    System.out.println("User '" + user1 + "' is valid: " + isValidUsername(user1));
    System.out.println("User '" + user2 + "' is valid: " + isValidUsername(user2));
    System.out.println("User '" + user3 + "' is valid: " + isValidUsername(user3));
  }
}

import java.net.URLDecoder;
import java.nio.charset.StandardCharsets;

public class PathCanonicalizer {
  public static String canonicalizePath(String path) {
    try {
      // 1. URL Decode the path
      String decodedPath = URLDecoder.decode(path, StandardCharsets.UTF_8.name());
      
      // 2. Normalize path separators (e.g., replace backslashes with forward slashes)
      decodedPath = decodedPath.replace("\\", "/");
      
      // 3. Remove redundant path elements (e.g., /./)
      decodedPath = decodedPath.replace("/./", "/");
      
      // Note: Full path traversal prevention requires more complex logic
      // and often involves resolving the path against a base directory.
      
      return decodedPath;
    } catch (Exception e) {
      return null; // Handle decoding errors
    }
  }

  public static void main(String[] args) {
    String input1 = "/usr/local/%2E%2E/etc/passwd";
    String input2 = "/app/data/./report.txt";

    System.out.println("Original: " + input1 + "\nCanonical: " + canonicalizePath(input1));
    System.out.println("\nOriginal: " + input2 + "\nCanonical: " + canonicalizePath(input2));
  }
}

public class DataTypeEnforcer {
  public static Integer parseIntegerSafely(String input) {
    if (input == null || input.trim().isEmpty()) {
      return null; // Or throw an IllegalArgumentException
    }
    try {
      return Integer.parseInt(input.trim());
    } catch (NumberFormatException e) {
      System.err.println("Error: '" + input + "' is not a valid integer.");
      return null; // Indicate failure
    }
  }

  public static void main(String[] args) {
    String validNum = "12345";
    String invalidNum = "abc";
    String negativeNum = "-50";

    System.out.println("Parsed '" + validNum + "': " + parseIntegerSafely(validNum));
    System.out.println("Parsed '" + invalidNum + "': " + parseIntegerSafely(invalidNum));
    System.out.println("Parsed '" + negativeNum + "': " + parseIntegerSafely(negativeNum));
  }
}