//往SD卡写入文件的方法    public void savaFileToSD(String filename, String filecontent) throws Exception {        //如果手机已插入sd卡,且app具有读写sd卡的权限        if (Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)) {            filename = Environment.getExternalStorageDirectory().getCanonicalPath() + "/" + filename;            //这里就不要用openFileOutput了,那个是往手机内存中写数据的            FileOutputStream output = new FileOutputStream(filename);            output.write(filecontent.getBytes());            //将String字符串以字节流的形式写入到输出流中            output.close();            //关闭输出流        } else Toast.makeText(context, "SD卡不存在或者不可读写", Toast.LENGTH_SHORT).show();    }    //读取SD卡中文件的方法    //定义读取文件的方法:    public String readFromSD(String filename) throws IOException {        StringBuilder sb = new StringBuilder("");        if (Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)) {            filename = Environment.getExternalStorageDirectory().getCanonicalPath() + "/" + filename;            //打开文件输入流            FileInputStream input = new FileInputStream(filename);            byte[] temp = new byte[1024];            int len = 0;            //读取文件内容:            while ((len = input.read(temp)) > 0) {                sb.append(new String(temp, 0, len));            }            //关闭输入流            input.close();        }        return sb.toString();    }

/*摘自菜鸟教程,侵删*/

//权限