Android:文件读写.

    //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

<!-- 在SDCard中创建与删除文件权限 -->
<uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS"/>
<!-- 往SDCard写入数据权限 -->
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>