Quick Tour of Controlling Applications

See How to Restrict Applications

As you saw in the previous step, a security manager is not automatically installed when an application is running. To apply the same security policy to an application found on the local file system as to downloaded applets, you can invoke the interpreter with the new -Djava.security.manager command line argument.

To execute the GetProps application with the default security manager, type the following:

java -Djava.security.manager GetProps

Here's the output from the program:

C:\TEST>java -Djava.security.manager GetProps
    About to get os.name property value
      The name of your operating system is: Windows 95
    About to get java.version property value
      The version of the JVM you are running is: JDK 1.2
    About to get user.home property value
    Caught exception java.security.AccessControlException: access denied (java.util.
      PropertyPermission user.home read)

The process is shown in the following figure.

Security-Sensitive Properties

The system policy file, loaded by default, grants all code permission to access some commonly useful properties such as "os.name" and "java.version". These properties are not security-sensitive, so granting such permissions does not pose a problem.

The other properties GetProps tries to access, "user.home" and "java.home", are not among the properties for which the system policy file grants read permission. Thus as soon as GetProps attempts to access the first of these properties ("user.home"), the security manager prevents the access and reports an AccessControlException. This exception indicates that the policy currently in effect, which consists of entries in one or more policy files, doesn't allow permission to read the "user.home" property.

The System Policy File

The system policy file is by default located at:

  Windows:
    java.home\lib\security\java.policy  
  UNIX:
    java.home/lib/security/java.policy  

Note that java.home represents the value of the "java.home" property, which is a system property specifying the directory into which the JDK was installed. Thus if the JDK was installed in the directory named C:\jdk1.2 on Windows and /jdk1.2 on UNIX, the system policy file is located at

  Windows:
    C:\jdk1.2\lib\security\java.policy  
  UNIX:
    /jdk1.2/lib/security/java.policy  

Here is a copy of the system policy file.

Quick Tour of Controlling Applications