在LINUX下每個檔案都有一個許可權的屬性 ，那麼在Android中怎麼用java改變某個檔案的許可權呢？

Android中有兩種方法可以改變檔案的許可權

1. 用openFileOutput方法：

1. FileOutputStream fos;    
2. fos = openFileOutput("filename", MODE_WORLD_READABLE);   

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 引數如下：

    /**
     * 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;

其實該方法最終還是呼叫了系統的chmod來實現的改變檔案許可權的功能。

但是該方法有侷限性，他建立的檔案只能位於該程式的私有目錄下，即/data/data/app-package/files/

2. 用Runtime.getRuntime().exec()

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

該方法呼叫系統命令chmod來改變檔案的許可權，為了能判斷命令的返回值，最好寫成：

1. Process p = Runtime.getRuntime().exec("chmod 644 " + filename);    
2. int status = p.waitFor();    
3. if (status == 0) {    
4.     //chmod succeed  
5. } else {    
6.     //chmod failed  
7. }