Java判断图片格式

public static String getImageType() throws IOException {   
           FileInputStream fis = new FileInputStream("PATH");   
       
    int leng = fis.available();   
    BufferedInputStream buff = new BufferedInputStream(fis);   
    byte[] mapObj = new byte[leng];   
    buff.read(mapObj, 0, leng);   
  
    String type = "";   
    ByteArrayInputStream bais = null;   
    MemoryCacheImageInputStream mcis = null;   
    try {   
        bais = new ByteArrayInputStream(mapObj);   
        mcis = new MemoryCacheImageInputStream(bais);   
        Iterator itr = ImageIO.getImageReaders(mcis);   
        while (itr.hasNext()) {   
        ImageReader reader = (ImageReader)  tr.next();   
            if (reader instanceof GIFImageReader) {   
                type = "gif";   
            } else if (reader instanceof JPEGImageReader) {   
                type = "jpeg";   
            } else if (reader instanceof PNGImageReader) {   
                type = "png";   
            } else if (reader instanceof BMPImageReader) {   
                type = "bmp";   
            }   
        }   
    } finally {   
        if (bais != null) {   
            try {   
                bais.close();   
            } catch (IOException ioe) {   
  
            }   
        }   
  
        if (mcis != null) {   
            try {   
                mcis.close();   
            } catch (IOException ioe) {   
  
            }   
        }   
    }   
    return type;   
}