Added a basic input validation for shortUrl

src/main/java/tk/draganczuk/url/Utils.java

@@ -1,10 +1,14 @@
 package tk.draganczuk.url;
 
 import java.util.Random;
+import java.util.regex.Pattern;
 
 public class Utils {
 	private static final Random random = new Random(System.currentTimeMillis());
 
+	private static final String SHORT_URL_PATTERN = "[a-z0-9]+";
+	private static final Pattern PATTERN = Pattern.compile(SHORT_URL_PATTERN);
+
 	public static String randomString() {
 		int leftLimit = 48; // numeral '0'
 		int rightLimit = 122; // letter 'z'
@@ -18,4 +22,9 @@ public class Utils {
 						StringBuilder::append)
 				.toString();
 	}
+
+	public static boolean validate(String shortUrl) {
+		return PATTERN.matcher(shortUrl)
+				.matches();
+	}
 }