Java in a Nutshell, 5th Edition

Name

PrivilegedAction<T>

Synopsis

This interface defines a block of code (the run( ) method) that is to be executed as privileged code by the AccessController.doPrivileged( ) method. In Java 5.0 this interface is generic and the type variable T represents the return type of the run( ) method. When privileged code is run with the doPrivileged( ) method, the AccessController looks only at the permissions of the immediate caller, not the permissions of the entire call stack. The immediate caller is typically fully trusted system code that has a full set of permissions, and therefore the privileged code runs with that full set of permissions, even if the system code is invoked by untrusted code with no permissions whatsoever.

Privileged code is typically required only when you are writing a trusted system library (such as a Java extension package) that must read local files or perform other restricted actions, even when called by untrusted code. For example, a class that must call System.loadLibrary( ) to load native methods should make the call to loadLibrary( ) within the run( ) method of a PrivilegedAction. If your privileged code may throw a checked exception, implement it in the run( ) method of a PrivilegedExceptionAction instead.

Be very careful when implementing this interface. To minimize the possibility of security holes, keep the body of the run( ) method as short as possible.

public interface PrivilegedAction<T> {
// Public Instance Methods
     T run( );  
}

Passed To

AccessController.doPrivileged( ...