presentnode.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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* 
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* software without specific prior written permission. 
*
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package issrg.pba.rbac.xmlpolicy.ifstatement;

/**
 * This is the class for Present node of the IF-statement. Its functionality is
 * very much determined by OperationNode and PresentInterpreter, which are 
 * configured to deliver the following semantics:
 *
 * <p>This operation expects one and only one Term, which must either be
 * an ArgNode or EnvironmentNode and returns a 
 * value of type Types.BOOLEAN_TYPE.
 * The evaluation result is "true", if and only if the Term refers to an 
 * argument or environmental variable that is present in the current 
 * Environment.
 *
 * @author A.Otenko
 */

public class PresentNode extends OperationNode {

  public static final String PRESENT_NODE = "Present";

  /**
   * Call this method to register the PresentNode with the XMLPolicyParser. It 
   * also
   * registers the default PresentInterpreter.
   */
  public static void register(){
    try{
      issrg.pba.rbac.xmlpolicy.XMLPolicyParser.registerXMLNode(PRESENT_NODE, PresentNode.class);
    }catch (NoSuchMethodException nsme){
      nsme.printStackTrace();
    }

    TermNode.registerInterpreterForNode(PRESENT_NODE, new PresentInterpreter());
  }

  protected PresentNode() {
  }

  /**
   * This constructor builds a PresentNode given the XMLPolicyParser and the 
   * set of
   * attributes of this XML element. It expects that there is one and only one
   * child node.
   *
   * @param p - the XMLPolicyParser that builds this PresentNode
   * @param attrs - the attributes of this XML element
   */
  public PresentNode(issrg.pba.rbac.xmlpolicy.XMLPolicyParser p, org.xml.sax.Attributes attrs){
    super(PRESENT_NODE, attrs, 1, 1);
  }

  /**
   * This method checks that there is only one child element in XML, and
   * that it is of type ArgNode or EnvironmentNode to ensure the semantic 
   * correctness of XML policy.
   */
  public void construct() throws issrg.pba.rbac.PolicyParsingException {
    super.construct();  // this has ensured there is a node, the only one.

    Object o = getChildren().get(0);  // there should be one
    if (!(o instanceof ArgNode) && !(o instanceof EnvironmentNode)){
      throw new issrg.pba.rbac.PolicyParsingException(PRESENT_NODE+" can have only "+ArgNode.ARG_NODE+" or "+EnvironmentNode.ENVIRONMENT_NODE+" as a child");
    }
  }
}


/**
 * This is the default Interpreter for the Present node. It ensures that 
 * it is asked to
 * interpret the right terms and returns the boolean result: true, if the Arg 
 * or Environment
 * parameter is present in the environmental settings; false otherwise.
 *
 * @author A.Otenko
 */
class PresentInterpreter implements Interpreter{
  public PresentInterpreter(){}

  /**
   * This method checks that the array of Terms has one and only one element,
   * and that it is ArgNode or EnvironmentNode.
   *
   * @param t - the array of Terms
   *
   * @return Types.BOOLEAN_TYPE, if the array of Terms has only one element,
   *   and that its class is either ArgNode or EnvironmentNode; otherwise null
   */
  public String canEvaluate(Term [] t){
    if (t.length==1 && ((t[0] instanceof ArgNode) || (t[0] instanceof EnvironmentNode))){
      return Types.BOOLEAN_TYPE;
    }else{
      return null;
    }
  }

  /**
   * This method verifies that the expression can be evaluated and returns a 
   * java.lang.Boolean with value set to
   * "true", if the specified Arg or Environment parameter is present in the
   * given Environment.
   *
   * @param env - the evaluation Environment with environmental parameters and
   *   action arguments in it
   * @param t - the array of actual Terms
   *
   * @return java.lang.Boolean object with the value set to "true", if the
   *   argument or environmental parameter named by the first Term in the array
   *   is present in it; otherwise it is set to "false"
   */
  public Object evaluate(Environment env, Term [] t) throws EvaluationException {
    java.util.Map m = t[0] instanceof ArgNode ? env.getArgs(): env.getEnv();

    if (canEvaluate(t)==null || m==null){
      throw new EvaluationException("Cannot evaluate expression");
    }

    String s = t[0] instanceof ArgNode ? ((ArgNode)t[0]).parameter_name :((EnvironmentNode)t[0]).parameter_name;

    return new Boolean(m.get(s)!=null);
  }
}