Java で日付文字列を特定の形式に対して検証するにはどうすればよいですか?

<code class="java">import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;

public class DateFormatter {

    public static boolean isValidFormat(String format, String value) {
        Date date = null;
        SimpleDateFormat sdf = new SimpleDateFormat(format);
        try {
            date = sdf.parse(value);
            if (!value.equals(sdf.format(date))) {
                date = null;
            }
        } catch (ParseException e) {
            // Date parsing failed
        }
        return date != null;
    }

    public static void main(String[] args) {
        System.out.println("isValid - dd/MM/yyyy with 20130925 = " + isValidFormat("dd/MM/yyyy", "20130925"));
        System.out.println("isValid - dd/MM/yyyy with 25/09/2013 = " + isValidFormat("dd/MM/yyyy", "25/09/2013"));
        System.out.println("isValid - dd/MM/yyyy with 25/09/2013 12:13:50 = " + isValidFormat("dd/MM/yyyy", "25/09/2013  12:13:50"));
        System.out.println("isValid - yyyy-MM-dd with 2017-18--15 = " + isValidFormat("yyyy-MM-dd", "2017-18--15"));
    }
}</code>

isValid - dd/MM/yyyy with 20130925 = false
isValid - dd/MM/yyyy with 25/09/2013 = true
isValid - dd/MM/yyyy with 25/09/2013 12:13:50 = false
isValid - yyyy-MM-dd with 2017-18--15 = false