andnode.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 
* modification, are permitted provided that the following conditions are met:
*
* 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 
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 
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* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 
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package issrg.pba.rbac.xmlpolicy.ifstatement;

/**
 * This is the class for And node of the IF-statement. Its functionality is
 * very much determined by OperationNode and AndInterpreter, which are 
 * configured to deliver the following semantics:
 *
 * <p>This operation expects one or more Terms, each returning a 
 * Types.BOOLEAN_TYPE type, and returns a value of type Types.BOOLEAN_TYPE.
 * The evaluation result is "true", if and only if all Terms of the AndNode
 * evaluate to boolean "true".
 *
 * @author A.Otenko
 */

public class AndNode extends OperationNode {

  public static final String AND_NODE = "AND";

  /**
   * Call this method to register the node with the XMLPolicyParser. This 
   * method also registers the default AndInterpreter.
   */
  public static void register(){
    try{
      issrg.pba.rbac.xmlpolicy.XMLPolicyParser.registerXMLNode(AND_NODE, AndNode.class);
    }catch (NoSuchMethodException nsme){
      nsme.printStackTrace();
    }

    issrg.pba.rbac.xmlpolicy.ifstatement.OperationNode.registerInterpreterForNode(AND_NODE, new AndInterpreter());
  }

  protected AndNode() {
  }

  /**
   * This constructor builds an AndNode, given a XMLPolicyParser and the
   * set of attributes of this XML element.
   *
   * @param p - the XMLPolicyParser that builds this AndNode
   * @param attrs - the attributes of this XML element
   */
  public AndNode(issrg.pba.rbac.xmlpolicy.XMLPolicyParser p, org.xml.sax.Attributes attrs){
    super(AND_NODE, attrs, -1, 1);
  }
}


/**
 * This is the default AndInterpreter that can evaluate the expression 
 * consisting of any number of Terms of type Types.BOOLEAN_TYPE. It returns
 * a boolean "true" if and only if all of the Terms evaluate
 * to boolean "true".
 */
class AndInterpreter implements Interpreter {
  public AndInterpreter(){}

  /**
   * This method returns Types.BOOLEAN_TYPE if the array length is non-zero, and
   * each Term is of type Types.BOOLEAN_TYPE.
   *
   * @param t - the array of Terms; must have non-zero length
   *
   * @return Types.BOOLEAN_TYPE if the array length is non-zero and all Terms
   *   in it return Types.BOOLEAN_TYPE on call to getType()
   */
  public String canEvaluate(Term [] t){
    if (t==null || t.length==0){
      return null;
    }

    for (int i=0; i<t.length; i++){
      if (t[i].getType().intern()!=Types.BOOLEAN_TYPE){ // all of the terms must be a boolean
        return null;
      }
    }

    return Types.BOOLEAN_TYPE;
  }

  /**
   * This method evaluates the given expression, so that a boolean "true" is 
   * returned if all of the Terms evaluate to boolean "true". Note
   * that not all of the Terms may be evaluated as the result (once a Term that
   * evaluates to "false" is found, evaluation of any further Terms is 
   * pointless).
   *
   * @param env - the Environment of evaluation
   * @param t - the array of Terms
   *
   * @return java.lang.Boolean object with the result of evaluation; it is
   *   set to "false" if there is at least one Term that evaluates to "false";
   *   otherwise it is set to "true"
   */
  public Object evaluate(Environment env, Term [] t) throws EvaluationException {
    if (canEvaluate(t)==null){
      throw new EvaluationException("Cannot evaluate expression");
    }

    Object result=null;
    for (int i=0; i<t.length; i++){ // the loop will always be executed at least once.
      result = t[i].evaluate(env);

      // it should be Boolean
      if (!((Boolean)result).booleanValue()){
        break;  // no point to evaluate further
      }
    }

    return result;
  }
}