add email validation method

Author: samfert

src/main/java/io/spring/Util.java

@@ -4,4 +4,8 @@ public class Util {
   public static boolean isEmpty(String value) {
     return value == null || value.isEmpty();
   }
+  
+  public static boolean isValidEmail(String email) {
+    return email != null && email.contains("@")
+  }
 }