在Android中通过Java修改文件权限

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：

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FileOutputStream fos;

fos = openFileOutput("filename", MODE_WORLD_READABLE);

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

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()

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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：

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

int status = p.waitFor();

if (status == 0) {

//chmod succeed

} else {

//chmod failed

}

Android在apk内部，即通过java代码来进行修改系统文件或者修改系统设置等等，这样需要获取系统权限。

通过直接配置apk运行在System进程内

1. 在应用程序的AndroidManifest.xml中的manifest节点中加入android:sharedUserId="android.uid.system"这个属性。

2. 修改Android.mk文件，加入LOCAL_CERTIFICATE := platform这一行

3. 使用mm命令来编译，生成的apk就有系统权限权限了。