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 = canReadExtension("yourExtensionName");
b = canReadExtension("gif");
b = canReadExtension("giF");
}
public static boolean canReadExtension(String fileExt) {
Iterator iter = ImageIO.getImageReadersBySuffix(fileExt);
return iter.hasNext();
}
}