BufferedImage转为base64

public Map getVerificationCode(HttpServletResponse response) {
        Map result = new HashMap();
        try {
            int width=200;
            int height=69;
            //生成对应宽高的初始图片
            BufferedImage verifyImg=new 
            BufferedImage(width,height,BufferedImage.TYPE_INT_RGB);
            //单独的一个类方法，出于代码复用考虑，进行了封装。
            String randomText = VerifyCode.drawRandomText(width,height,verifyImg);
            //功能是生成验证码字符并加上噪点，干扰线，返回值为验证码字符
            response.setContentType("image/png");//必须设置响应内容类型为图片，否则前台不识别
            //将图片转换陈字符串给前端
            ByteArrayOutputStream stream = new ByteArrayOutputStream();
            ImageIO.write(verifyImg, "png", stream);
            String base64 = Base64.encode(stream.toByteArray());
            stream.flush();
            stream.close();
            //封装数据
            String uuid = IDTool.getUUID32();
            result.put("image", "data:image/png;base64,"+base64);
            result.put("uuid", uuid);
            redisUtil.set("verifyCode:"+uuid,randomText.toLowerCase(),5L, 
                           TimeUnit.MINUTES);


        } catch (IOException e) {
            e.printStackTrace();

        }
        return result;
    }