javax.imageio 
类 ImageIO
BufferedImage bi = ImageIO.read(resFile);//resFile --- InputStream

if(bi == null){ 
   System.out.println(此文件不为图片文件);
}


 


try {//判断是否为图片文件并且返回图片的格式！
            
            ImageInputStream iis = ImageIO.createImageInputStream(o);
    
            // Find all image readers that recognize the image format
            Iterator<ImageReader> iter = ImageIO.getImageReaders(iis);
            if (!iter.hasNext()) {
                // No readers found
                return null;
            }
    
            // Use the first reader
            ImageReader reader = iter.next();
    
            // Close stream
            iis.close();
    
            // Return the format name
            return reader.getFormatName();
}

加载一个图片：
ImageIcon(byte[] imageData, String description)