android 操作 sd 卡上的文件

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        
        try{
            write("cai.sq","welcome to the hell");
            String str = read("cai.sq");
            Log.v("sq", str);
        }catch(IOException e){e.printStackTrace();}
    }
    String read(String fileName)throws IOException
    {
        StringBuilder sb = new StringBuilder();
        if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED))//判断sd卡是否已将插上，并且应用程序有读的权限
        {
            File sdCardDir = Environment.getExternalStorageDirectory();        //获取sd卡对应的存储目录
            FileInputStream fis = new FileInputStream(sdCardDir.getCanonicalFile() +"/" + fileName);// 获得指定文件对应的输入流
            BufferedReader br = new BufferedReader(new InputStreamReader(fis));    //转化为缓冲流
            String line=null;
            while((line = br.readLine())!=null)
            {
                sb.append(line);
            }
            br.close();
            fis.close();
            return sb.toString();
        }else
        return null;
    }
    
    void write(String fileName,String content) throws IOException
    {
        if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED))//判断sd卡是否已将插上，并且应用程序有读的权限
        {
            File sdCardDir = Environment.getExternalStorageDirectory();        //获取sd卡对应的存储目录
            File targerFile = new File(sdCardDir.getCanonicalFile() +"/"+ fileName);    //获取目标文件
            RandomAccessFile raf = new RandomAccessFile(targerFile, "rw");        //“rw”表示可读可写
            raf.seek(targerFile.length());    //将文件指针移到文件末尾，为了追加数据
            raf.write(content.getBytes());    //写数据
            raf.close();
        }
    }
　　//不要忘了在 manifest 中赋予权限
　　//    <uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS"/>  <!-- 注册： 挂载、卸载文件系统的权限 -->
    
   //     <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>   <!-- 注册： 向SD 卡写入数据的权限 -->