defaultcredentialbehaviour.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
* All rights reserved.
*
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*
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* list of conditions and the following disclaimer.
* 
* Redistributions in binary form must reproduce the above copyright notice, 
* this list of conditions and the following disclaimer in the documentation 
* and/or other materials provided with the distribution. 
*
* Neither the name of the University of Salford nor the names of its 
* contributors may be used to endorse or promote products derived from this 
* software without specific prior written permission. 
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" 
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 
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* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 
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*/

package issrg.pba.credentials;

/**
 * This class defines the default behaviour of the credential: the equals method,
 * the methods for intersection and union operations.
 */

public abstract class DefaultCredentialBehaviour implements Credential {

  private boolean busy=false;   // this is a flag to prevent endless recursion in intersect
  private boolean busy1=false;   // this is a flag to prevent endless recursion in join

  protected DefaultCredentialBehaviour() {}

  public boolean equals(Object o){
    if (o instanceof Property){
      Property p = (Property)o;
      return p.contains(this) && this.contains(p);
    }else{
      return false;
    }
  }

  /**
   * The default contains operation says that all null properties are contained by
   * any other property (returns true, if property is null)
   */
  public boolean contains(Property p){
    if (p instanceof Sum){
      return ((Sum)p).partOf(this);
    }

    if (p instanceof Product){
      return ((Product)p).partOf(this);
    }
    return p==null;
  }

  /**
   * The default intersection operation returns lhs (this) credential if it contains the
   * rhs one (passed to the method); otherwise it returns the result of intersecting
   * the rhs credential with lhs one.
   */
  public synchronized Credential intersect(Credential c){
    if (busy){
      return null;
    }

    if (contains(c)){
      return c;
    }

    if (c instanceof Product || c instanceof Sum){
      return c.intersect(this);
    } else {
      busy=true;
      Credential r=null;
      try{
        //if (!c.busy){   // if that credential is not being intersected with already
          r=c.intersect(this);
        //}
      }catch(RuntimeException th){
        throw th;
      }finally{
        busy=false;
      }

      return r;
    }
  }

  /**
   * The default union operation returns lhs (this) credential if it contains the
   * rhs one; otherwise it returns the union of rhs and lhs ( c.join(this) ).
   */
  public synchronized Credential join(Credential c){
    if (busy1){
      return new Sum(new Credential[]{this, c});
    }

    if (contains(c)){
      return this;
    }

    if (c instanceof Sum){
      return c.join(this);
    }else {
      busy1=true;

      Credential r;
      try{
        //if (!c.busy1){  // if that credential is not being joined with already
          r=c.join(this);
        //}else{
        //  r=new Sum(new Credential[]{this, c});
        //}
      }catch(RuntimeException th){
        throw th;
      }finally{
        busy1=false;
      }

      return r;
    }
  }
}