转自 http://elim.iteye.com/blog/1187394

    /**
     * 上传图片
     * @param base64 图片编码后的字符串
     * @return 上传成功后的文件名
     */
    public static String upload(String base64) {
        String dir = getRequest().getRealPath(UPLOAD_PATH);
        File fileLocation = new File(dir);
        String fileType = base64.substring(11, 14);
        if(!fileLocation.exists()) {
            boolean isCreated  = fileLocation.mkdir();
            if(!isCreated) {
                //目标上传目录创建失败,可做其他处理,例如抛出自定义异常等,一般应该不会出现这种情况。
                return null;
            }
        }
        if(base64.indexOf("jpeg") != -1) {
            //存在jpeg文件的情况
            base64 = base64.replaceFirst("jpeg", "jpg");
        }
        String tempStr = UUID.randomUUID().toString()+System.currentTimeMillis();
        
        String upName = tempStr+"."+fileType;
        FileOutputStream out;
        String iconBase64 = base64.substring(22);
        try {
            byte[] buffer = new BASE64Decoder().decodeBuffer(iconBase64);
            out = new FileOutputStream(dir+"/"+upName);
            out.write(buffer);
            out.close();
            
            String upNameXhdpi = tempStr+"-xhdpi."+fileType;
            String upNameMhdpi = tempStr+"-mhdpi."+fileType;
            
            FileOutputStream outXhdpi = new FileOutputStream(dir+"/"+upNameXhdpi);
            FileOutputStream outMhdpi = new FileOutputStream(dir+"/"+upNameMhdpi);
            
            resizeImage(iconBase64, outXhdpi, xhdpi, fileType);
            resizeImage(iconBase64, outMhdpi, mhdpi, fileType);
            
            return PATH+UPLOAD_PATH + "/" +upName;
        } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
            return null;
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
            return null;
        }
    }

    /**
     * 改变图片的大小到宽为size，然后高随着宽等比例变化
     * @param is 上传的图片的输入流
     * @param os 改变了图片的大小后，把图片的流输出到目标OutputStream
     * @param size 新图片的宽
     * @param format 新图片的格式
     * @throws IOException
     */
    public static void resizeImage(String is, OutputStream os, int size, String format) throws IOException {
        ByteArrayInputStream in = new ByteArrayInputStream(new BASE64Decoder().decodeBuffer(is));
        BufferedImage prevImage = ImageIO.read(in);  
        double width = prevImage.getWidth();
        double height = prevImage.getHeight();
        double percent = size/width;
        int newWidth = (int)(width * percent);
        int newHeight = (int)(height * percent);
        BufferedImage image = new BufferedImage(newWidth, newHeight, BufferedImage.TYPE_INT_BGR);
        Graphics graphics = image.createGraphics();
        graphics.drawImage(prevImage, 0, 0, newWidth, newHeight, null);
        ImageIO.write(image, format, os);
        os.flush();
        in.close();
        os.close();
    }

upload方法中xhdpi和mhdpi是指不同大小的数字，上传上来的base64是包含头的，例如这样的base64字符串

data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAIAAAACACAYAAADDPmHLAAAABGdBTUEAALGPC/xhBQAAACBjSFJNAAB6JgAAgIQAAPoAAACA6AAAdTAAAOpgAAA6mAAAF3CculE8AAAABmJLR0QAAAAAAAD5Q7t/AAAACXBIWXMAAAsSAAALEgHS3X78AAAI4ElEQVR42u2d2W7b2AGGP1KkRFGStdnxmgToFdHkJfICc9lO537ay2IuivYN2r7HtDOZmwJ9gE4fogPwaprFBmzHlmTtC5deKFQVL7HiiDo85PkAw7AsSD91PpGHZ9X4CK7rPgG+Al4AvwR2gAKKJNMHjoHXwL+Bl47j/PeuJ2u3Pfi+4P8C/ArIiT4ixWcRAC+BPzmO8+b6P28I4LruF8C3QEV0csVa6QO/dRznu+UH9eU/XNf9PfAPVOGnkTLwN9d1v1l+cHEGcF3318B33HFZUKSGEPiN4zgv4X1hv7/