public class Test2 {

    public static void main(String[] args) {        
        String str = " <br/> <br/> <br/> aafsdf\n" +
            "fas <br/> dfsdf\n" +
            " <br/>";
        String regex = "(?i)\\A(?:\\s*<br\\s*/>)+\\s*|(?:\\s*<br\\s*/>)+\\s*\\Z";
        str = str.replaceAll(regex, "");
        System.out.println(str);
    }
}