subsetcredentials.java

一个完整的XACML工程,学习XACML技术的好例子!

/*
* Copyright (c) 2000-2005, University of Salford
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* software without specific prior written permission. 
*
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package issrg.pba.rbac;

import issrg.pba.Credentials;

/**
 * This abstract class defines some basic behaviour, taking into account that
 * a SetOfSubsets class exists. 
 *
 * @author A Otenko
 * @version 1.0
 */

public abstract class SubsetCredentials implements Credentials {
  protected SubsetCredentials() {
  }

  /**
   * This method tells if the given set of credentials is contained within this
   * credentials object. If the credentials object is a SetOfSubsetsCredentials 
   * it deploys its
   * <code>partOf</code> method. All of the subclasses should call this method,
   * if they do not handle a SetOfSubsetsCredentials.
   *
   * @param cred is the credential to compare
   *
   * @return true if the given credential is contained within this credential
   *
   * @see SetOfSubsetsCredentials
   */
  public boolean contains(Credentials cred){
    if (cred instanceof SetOfSubsetsCredentials){
      return ((SetOfSubsetsCredentials)cred).partOf(this/*cred*/); //Tuan Anh: why Sassa used "cred" here? it always return true!!
    }

    return false;
  }

  /**
   * This method compares two credentials for equality. The result is equal to
   * <p><code>contains(cred) && cred.contains(this)</code>,
   * <p>if cred is
   * a credentials object. The result is always false if cred is not a 
   * Credentials object.
   *
   * @param cred is the object to compare with
   *
   * @result true, if the objects are equal
   */
  public boolean equals(Object cred){
    if (cred instanceof Credentials){
      Credentials c = (Credentials)cred;
      return c.contains(this) && this.contains(c);
    }

    return false;
  }

  /**
   * This method implements the basic intersection rule: the intersection is
   * the biggest common part. In particular, if this object 
   * contains
   * the other object, then the intersection is that object; if this object is
   * contained within the other object, then the intersection is this object.
   * Otherwise the intersection is null.
   *
   * @param cred is the credential to intersect with
   *
   * @return the Credential that is the intersection of the two
   */
  public Credentials intersection(Credentials cred){
    /*
    *
    * <p>TODO: do I change it to call some other protected method to determine the
    * actual intersection?
    */
    if (contains(cred)){
      return cred;
    }

    if (cred.contains(this)){
      return this;
    }

    return null;
  }

  /**
   * This method implements the default behaviour for the union operation: the
   * union is the smallest set containing both objects. In particular, if
   * cred contains this object, then the result is cred; if this object 
   * contains cred, then
   * the result is this. Otherwise the union is a SetOfSubsetsCredential,
   * containing both.
   *
   * @param cred is the credentials object to join with
   *
   * @return the Credentials object that is the union of the two
   */
  public Credentials union(Credentials cred){
    if (contains(cred)){
      return this;
    }

    if (cred.contains(this)){
      return cred;
    }

    return new SetOfSubsetsCredentials(new Credentials []{this, cred});
  }

  /**
   * This method creates a copy of the credentials object. Requires
   * overriding in implementations of subclasses.
   */
  public abstract Object clone();
}