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) 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()
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
}