java 代码判断图片格式后缀名称

 /**
 * 图片判断
 */
private static String getFormatName(Object o) {  
     try {  
         // Create an image input stream on the image  
         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 = (ImageReader) iter.next();  
  
         // Close stream  
         iis.close();  
  
         // Return the format name  
         return reader.getFormatName();  
     } catch (IOException e) {  
         //  
     }

     // The image could not be read  
     return null;  
 }