termnode.java

一个完整的XACML工程,学习XACML技术的好例子!

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package issrg.pba.rbac.xmlpolicy.ifstatement;

import issrg.pba.rbac.PolicyParsingException;
import issrg.pba.rbac.xmlpolicy.PolicyXMLNode;

/**
 * This abstract class represents XML elements that are Terms of IF-expressions.
 * It maintains a registry of Interpreters for each type of operation, which is
 * used indirectly by OperationNode and other subclasses.
 *
 * @author A.Otenko
 */
public abstract class TermNode extends PolicyXMLNode implements Term {
  protected int maxOperand;
  protected int minOperand;
  protected Term [] terms;

  private final static java.util.Map interpreters = new java.util.Hashtable();

  /**
   * This method registers an interpreter for a given type of operation.
   *
   * @param nodeName - the name of the XML element that represents the 
   *   operation
   * @param i - the Interpreter for that operation
   */
  protected static void registerInterpreterForNode(String nodeName, Interpreter i){
    java.util.Vector v = (java.util.Vector)interpreters.get(nodeName);
    if (v==null){
      v=new java.util.Vector();
      interpreters.put(nodeName, v);
    }

    v.add(i);
  }

  /**
   * This method retrieves an array of interpreters for a particular kind of 
   * operation.
   *
   * @param nodeName - the name of the XML element that represents the 
   *   operation
   *
   * @return an array of Interpreters for this kind of operation; can be null
   *   or empty if no Interpreters were registered for that kind of operation
   */
  protected static Interpreter[] getInterpretersForNode(String nodeName){
    java.util.Vector v = (java.util.Vector)interpreters.get(nodeName);
    Interpreter [] result = null;
    if (v!=null){
      Object [] o = v.toArray();
      result = new Interpreter[o.length];
      System.arraycopy(o, 0, result, 0, result.length);
    }

    return result;
  }

  protected TermNode(){
    super();
  }

  /**
   * This constructor builds a TermNode object that will check that the child 
   * nodes are
   * Terms and that there are not more than maxOperandCount of them and not 
   * less than minOperandCount.
   * The negative values of these two parameters mean no restriction on the 
   * amount of children.
   *
   * @param name is the name of the XML element for this operator
   * @param attr is the set of attributes it has got
   * @param maxOperandCount is the maximum amount of children allowed; -1 means 
   *   "don't care"
   * @param minOperandCouns is the minimum amount of children allowed; -1 means 
   *   "don't care"
   */
  public TermNode(String name, org.xml.sax.Attributes attr, int maxOperandCount, int minOperandCount){
    super(name, attr);

    maxOperand=maxOperandCount;
    minOperand=minOperandCount;
  }

  /**
   * This method ensures the children are Terms and that there are not more 
   * than maxOperandCount
   * and not less than minOperandCount of them, as specified in the 
   * constructor. It also creates
   * an array of Terms that can be used by the sub-classes in their 
   * evaluations.
   *
   * @throws PolicyParsingException if one of the above-stated conditions is 
   *   violated
   */
  public void construct() throws PolicyParsingException {
    java.util.Vector c = getChildren();

    if ((minOperand>=0 && c.size()<minOperand) || (maxOperand>=0 && c.size()>maxOperand)){
      throw new PolicyParsingException("Illegal number of operands (child nodes) for "+getName()+" node");
    }

    terms = new Term[c.size()];

    for (int i=0; i<c.size(); i++){
      if (c.get(i) instanceof Term){
        terms[i]=(Term)c.get(i);
        continue;
      }

      throw new PolicyParsingException("Operand ("+i+") "+((PolicyXMLNode)c.get(i)).getName()+" is not a valid term for "+getName()+" node");
    }
  }
}