The HighScore Class
The HighScore
class stores and protects access to the user's high score for ExampleGame
(and any other games that call it). For simplicity, this class saves the high score value into a file, called .highscore
, in the user's home directory. However, before allowing ExampleGame
to retrieve or update the user's high score value, this class checks to make sure that the user has granted ExampleGame
permission to access the high score in his/her security policy file.
Checking that ExampleGame
has the HighScorePermission
To check whether or not ExampleGame
has permission to access the user's high score, the HighScore
class must:
- Call
System.getSecurityManager()
to get the currently installed security manager. - If the result is not null (i.e., there is a security manager, as opposed to the caller being an application that is unrestricted), then
- Construct a
HighScorePermission
object, and - Call the security manager's
checkPermission
method, and pass it the newly constructedHighScorePermission
object.
- Construct a
Here is the code:
SecurityManager sm = System.getSecurityManager(); if (sm != null) { sm.checkPermission( new HighScorePermission(gameName)); }
The checkPermission
method essentially asks the security manager if ExampleGame
has the specified HighScorePermission
. In other words, it asks the security manager if ExampleGame
has permission to update the user's high score value for the specified game (ExampleGame
). The underlying security framework will consult the user's security policy to see if ExampleGame
indeed has this permission.
The HighScore Code
Here
is the complete source code for the HighScore
class.
Note: The doPrivileged
method calls are used to enable HighScore
to temporarily access resources that are available to it but that are not available to the code that calls it (ExampleGame
). For example, it is expected that the policy file will grant HighScore
permission to access the .highscore
file in the user's home directory, but it will not grant this permission to games, such as ExampleGame
.