MultipartFile file1 = file;

 CommonsMultipartFile cf= (CommonsMultipartFile)file1;

 DiskFileItem fi = (DiskFileItem)cf.getFileItem();

 File f = fi.getStoreLocation();

 private static Image img;

 private static float width;

 private static float height; 

 img = ImageIO.read(f);      // 构造Image对象

 width  =  Float.parseFloat(String.valueOf(img.getWidth(null)));  // 得到源图宽

 height =  Float.parseFloat(String.valueOf(img.getHeight(null))); // 得到源图长 

 System.out.println("输入的图片大小："+f.length()/1024+"kb");

 //判断文件是否能转化成image类

 if(width!=-1){

    //当前例子是等比例缩放到宽为320px

    //缩放比例

    Float s=width/320;

    //要缩放的宽

    Integer w=(int) (width/s);

    //要缩放的高

    Integer h=(int) (height/s);

    //创建一个模板

    BufferedImage image = new BufferedImage(w, h,BufferedImage.TYPE_INT_RGB);

    //在模板上绘制缩小后的图

    image.getGraphics().drawImage(img, 0, 0, w, h, null);

 }

ByteArrayOutputStream os = new ByteArrayOutputStream();

ImageIO.write(image, "gif", os);

InputStream is = new ByteArrayInputStream(os.toByteArray());