constantnode.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.
*
* Redistribution and use in source and binary forms, with or without 
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*
* Redistributions of source code must retain the above copyright notice, this 
* 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 
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 
* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE 
* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 
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package issrg.pba.rbac.xmlpolicy.ifstatement;

/**
 * This is the class that represents a Constant node and evaluates the contant 
 * specified
 * in the policy XML.
 *
 * <p>If the policy contains the constant of type for which there is no 
 * constructor provided
 * by the AEF (not registered with the Types), an EvaluationException will 
 * occur at construction-time.
 *
 * @author A.Otenko
 */

public class ConstantNode extends TermNode {
  /**
   * This is the name of the node that represents the Constant - a static value specified in
   * the policy.
   */
  public final static String CONSTANT_NODE = "Constant";

  /**
   * This method should be called to register the node with the XML Parser
   */
  public static void register(){
    try{
      issrg.pba.rbac.xmlpolicy.XMLPolicyParser.registerXMLNode(CONSTANT_NODE, ConstantNode.class);
    }catch (NoSuchMethodException nsme){
      nsme.printStackTrace();
    }
  }

  protected String type;
  protected Object value;

  protected ConstantNode() {}

  /**
   * This constructor builds an ConstantNode, given a XMLPolicyParser and the
   * set of attributes of this XML element. It expects that a 
   * issrg.pba.rbac.xmlpolicy.XMLTags.TYPE_ATTRIBUTE and 
   * issrg.pba.rbac.xmlpolicy.XMLTags.VALUE_ATTRIBUTE ("Type" and "Value") are 
   * present in this XML element. The value is converted from string into a
   * Java object using the Types.construct() method, so the type of the value
   * must be registered there.
   *
   * @param p - the XMLPolicyParser that builds this ConstantNode
   * @param attr - the attributes of this XML element
   *
   * @throws EvaluationException, if the value could not be decoded using 
   *   available types
   * @see Types#construct
   */
  public ConstantNode(issrg.pba.rbac.xmlpolicy.XMLPolicyParser p, org.xml.sax.Attributes attr) throws EvaluationException, issrg.pba.rbac.PolicyParsingException{
    super(CONSTANT_NODE, attr, -1, 0);

    type=((String)getAttributes().get(issrg.pba.rbac.xmlpolicy.XMLTags.TYPE_ATTRIBUTE)).intern();
    if (type==null) throw new issrg.pba.rbac.PolicyParsingException(issrg.pba.rbac.xmlpolicy.XMLTags.TYPE_ATTRIBUTE+" attribute was expected in "+CONSTANT_NODE);
    value = getAttributes().get(issrg.pba.rbac.xmlpolicy.XMLTags.VALUE_ATTRIBUTE);
    if (value==null) throw new issrg.pba.rbac.PolicyParsingException(issrg.pba.rbac.xmlpolicy.XMLTags.VALUE_ATTRIBUTE+" attribute was expected in "+CONSTANT_NODE);
    value = Types.construct(type, (String)value);
  }

  /**
   * This method returns the Type of the constant as determined at construction
   * time.
   */
  public String getType(){
    return type;
  }

  /**
   * This method returns the value of the constant evaluated at construction
   * time. It doesn't actually throw EvaluationExceptions, but the clause is
   * kept for subclasses, if there will be any.
   */
  public Object evaluate(Environment env) throws EvaluationException{
    return value;
  }
}