在LINUX下每个文件都有一个权限的属性 ，那么在Android中怎么用java改变某个文件的权限呢？

Android中有两种方法可以改变文件的权限

1. 用openFileOutput方法：

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 参数如下：

    /**
     * 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;

其实该方法最终还是调用了系统的chmod来实现的改变文件权限的功能。

但是该方法有局限性，他创建的文件只能位于该程序的私有目录下，即/data/data/app-package/files/

2. 用Runtime.getRuntime().exec()

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

该方法调用系统命令chmod来改变文件的权限，为了能判断命令的返回值，最好写成：

Process p = Runtime.getRuntime().exec("chmod 644 " + filename); int status = p.waitFor(); if (status == 0) { //chmod succeed } else { //chmod failed }