import java.io.File;
import java.util.Iterator;
import javax.imageio.ImageIO;
public class Main {
public static void main(String[] argv) throws Exception {
boolean b;
b = canReadFormat("yourExtensionName");
b = canReadFormat("gif");
b = canReadFormat("giF");
}
public static boolean canReadFormat(String formatName) {
Iterator iter = ImageIO.getImageReadersByFormatName(formatName);
return iter.hasNext();
}
}