java 判断图片的类型

// 这种方法如果遇到不是图片类型的文件会reader抛异常!  
public static void main(String[] args) throws IOException {
    	// get image format in a file
        File file = new File("C:/Users/dell、/Desktop/2.txt");

        // create an image input stream from the specified fileDD
        ImageInputStream iis = ImageIO.createImageInputStream(file);

        // get all currently registered readers that recognize the image format
        Iterator<ImageReader> iter = ImageIO.getImageReaders(iis);

        if (!iter.hasNext()) {
            throw new RuntimeException("No readers found!");
        }

        // get the first reader
        ImageReader reader = iter.next();

        System.out.println("Format: " + reader.getFormatName());

        // close stream
        iis.close();
	}