/**
     * 对图片进行压缩
     * @param srcfile    本地图片路径
     * @param imgdist    上传服务器路径
     * @param widthdist        压缩宽度
     * @param heightdist    压缩高度
     */
    public void reduceImg(File srcfile, File imgdist, int widthdist,int heightdist) {
        try {
            Image src = javax.imageio.ImageIO.read(srcfile);
            int width = src.getWidth(null);
            int height = src.getHeight(null);
            // 宽度除以高度的比例
            float wh = (float) width / (float) height;

            if (1 < wh) {
                float tmp_heigth = (float) widthdist / wh;
                BufferedImage tag = new BufferedImage(widthdist,(int) tmp_heigth, BufferedImage.TYPE_INT_RGB);
                tag.getGraphics().drawImage(src, 0, 0, widthdist,(int) tmp_heigth, null);
                FileOutputStream out = new FileOutputStream(imgdist);
                JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(out);
                encoder.encode(tag);
                out.close();
            } else {
                float tmp_width = (float) heightdist * wh;
                BufferedImage tag = new BufferedImage((int) tmp_width,heightdist, BufferedImage.TYPE_INT_RGB);
                tag.getGraphics().drawImage(src, 0, 0, (int) tmp_width,heightdist, null);
                FileOutputStream out = new FileOutputStream(imgdist);
                JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(out);
                encoder.encode(tag);
                out.close();
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

------解决方案--------------------
探讨

Image getScaledInstance(int width, int height, int hints)