openFileOutput 文件属性设置、主动配置文件的可读写属性及事实上现方式

首先參考

Android 内部存储相关的函数（getCacheDir,getDir, getFileStreamPath,getFilesDir,openFileInput, ...)

1. 用openFileOutput方法改变文件的属性，可是该方法有局限性，他创建的文件仅仅能位于该程序的私有文件夹下，即/data/data/app-package/files/。

    FileOutputStream fos;
    fos = openFileOutput("filename", MODE_WORLD_READABLE);   

FileOutputStream android.content.ContextWrapper.openFileOutput(String name, int mode) throws
FileNotFoundException

Open a private file associated with this Context's application package for writing. Creates the file if it doesn't already exist.

可用的mode 參数例如以下：

/**

     * File creation mode: the default mode, where the created file can only

     * be accessed by the calling application (or all applications sharing the

     * same user ID).

     * @see #MODE_WORLD_READABLE

     * @see #MODE_WORLD_WRITEABLE

     */

    public static final int MODE_PRIVATE = 0x0000;

    /**

     * File creation mode: allow all other applications to have read access

     * to the created file.

     * @see #MODE_PRIVATE

     * @see #MODE_WORLD_WRITEABLE

     */

    public static final int MODE_WORLD_READABLE = 0x0001;

    /**

     * File creation mode: allow all other applications to have write access

     * to the created file.

     * @see #MODE_PRIVATE

     * @see #MODE_WORLD_READABLE

     */

    public static final int MODE_WORLD_WRITEABLE = 0x0002;

    /**

     * File creation mode: for use with {@link #openFileOutput}, if the file

     * already exists then write data to the end of the existing file

     * instead of erasing it.

     * @see #openFileOutput

     */

    public static final int MODE_APPEND = 0x8000;

终于的实现方式剖析：

终于还是调用了系统的chmod来实现的改变文件权限的功能。

 Runtime.getRuntime().exec("chmod 644 " + filename);  

2. 用Runtime.getRuntime().exec()调用系统命令chmod来改变文件的权限，为了能推断命令的返回值，最好写成：