Added a basic input validation for shortUrl

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

@@ -1,5 +1,6 @@
 package tk.draganczuk.url;
 
+import org.eclipse.jetty.http.HttpStatus;
 import spark.Request;
 import spark.Response;
 
@@ -29,8 +30,14 @@ public class Routes {
 			shortUrl = Utils.randomString();
 		}
 
+		if (Utils.validate(shortUrl)) {
 			return urlFile.addUrl(longUrl, shortUrl);
+		} else {
+			res.status(HttpStatus.BAD_REQUEST_400);
+			return "shortUrl not valid ([a-z0-9]+)";
 		}
+	}
+
 
 	public static String goToLongUrl(Request req, Response res) {
 		String shortUrl = req.params("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();
+	}
 }

src/main/resources/public/index.html

@@ -30,11 +30,12 @@
             <legend>Add new URL</legend>
             <div class="pure-control-group">
                 <label for="longUrl">Long URL</label>
-                <input type="text" name="longUrl" id="longUrl" placeholder="Long URL" required/>
+                <input type="url" name="longUrl" id="longUrl" placeholder="Long URL" required/>
             </div>
             <div class="pure-control-group">
                 <label for="shortUrl">Short URL (Optional)</label>
-                <input type="text" name="shortUrl" id="shortUrl" placeholder="Short URL (optional)"/>
+                <input type="text" name="shortUrl" id="shortUrl" placeholder="Short URL (optional)"
+                       pattern="[a-z0-9]+"/>
             </div>
             <div class="pure-controls">
                 <button class="pure-button pure-button-primary">Submit</button>