ServletInputStream 获取数据编码问题

            String temporaryDirectory = request.getSession().getServletContext().getRealPath("/WEB-INF/upload/temporary_directory/" + "11.txt");
            ServletInputStream inputStream = request.getInputStream();
            FileOutputStream out = new FileOutputStream(temporaryDirectory);
            byte[] buf = new byte[1024];
            int len = inputStream.read(buf, 0, 1024);
            while(len > 0 && len != -1) {
                out.write(buf, 0, len);
                len = inputStream.read(buf, 0, 1024);
            }
            out.close();
            inputStream.close();

保存后文件是 UTF-8编码 的
file=data%3Aimage%2Fpng%3Bbase64%2CiVBORw0KGgoAAAANSUhEUgAAB28AABKeCAYAAADlcc...

而前台传的数据是：
data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAB28AABKeCAYAAADlcc
这个怎么处理，让他保存成 解码格式？

保存为data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAB28AABKeCAYAAADlcc格式

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Writer out = new BufferedWriter(new OutputStreamWriter(new FileOutputStream(temporaryDirectory), "UTF8"));