Security and Cryptography - Java Examples in a Nutshell - page 125

not standard system properties; they are properties that you must specify to the
Java interpreter when you run the SafeServer program. service.dir specifies the
directory from which the service classes are to be loaded. Assume here that they
are loaded via a local file: URL, not through an http: or other network URL. The
service.tmp property specifies a directory in which the service classes are allowed
to read and write temporary scratch files. SafeServer.policy demonstrates a syntax
that replaces the name of a system property with the value of that property. In this
way, the security policy file can be made somewhat independent of the installation
location of the application.
Example 6−2: SafeServer.policy
// This file grants the SafeServer class the permissions it needs to load
// Service classes through a URLClassLoader, and grants the Service classes
// permission to read and write files in and beneath the directory specified
// by the service.tmp system property. Note that you'll need to edit the
// URL that specifies the location of the SafeServer class, and that for
// Windows systems, you'll need to replace "/" with "\\"
// Grant permissions to the SafeServer class.
// Edit the directory for your system.
grant codeBase "file:/home/david/Books/JavaExamples2/Examples" {
// Allow the server to listen for and accept network connections
// from any host on any port > 1024
permission java.net.SocketPermission "*:1024-", "listen,accept";
// Allow the server to create a class loader to load service classes
permission java.lang.RuntimePermission "createClassLoader";
// Give the server permission to read the directory that contains the
// service classes. If we were using a network URL instead of a file URL
// we'd need to add a SocketPermission instead of a FilePermission
permission java.io.FilePermission "${service.dir}/-", "read";
// The server cannot grant permissions to the Service classes unless it
// has those permissions itself. So we give the server these two Service
// permissions.
permission java.util.PropertyPermission "service.tmp", "read";
permission java.io.FilePermission "${service.tmp}/-", "read,write";
};
// Grant permissions to classes loaded from the directory specified by the
// service.dir system property. If we were using a network URL instead of a
// local file: URL, this line would have to be different.
grant codeBase "file:${service.dir}" {
// Services can read the system property "service.tmp"
permission java.util.PropertyPermission "service.tmp", "read";
// And they can read and write files in the directory specified by
// that system property
permission java.io.FilePermission "${service.tmp}/-", "read,write";
};
Testing SafeServer
To demonstrate that SafeServer runs its services safely, you need a demonstration
service. Example 6-3 shows one such service that attempts various restricted
actions and reports its results. Note that since you're going to load this class with a