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

/**
 * This is the class that represents an Environment node and evaluates the 
 * environmental variables
 * at run-time.
 *
 * <p>EnvironmentNode expects the environment to contain either 
 * issrg.pba.rbac.Argument objects, in which case the string value will be 
 * converted using Types.construct, or other objects, which will be passed
 * as is to the interpreters.
 *
 * <p>If the environment contains the variables of types for which there is no 
 * constructor provided
 * by the AEF (not registered with the Types), or the AEF failed to provide the 
 * variable with the name
 * stated in the policy, an EvaluationException will occur at run-time.
 *
 * <p>Note that if the evaluation does not reach the point where the variable 
 * is needed, no
 * exception will be thrown.
 *
 * @see Types#construct
 *
 * @author A.Otenko
 */

public class EnvironmentNode extends TermNode {
  /**
   * This is the name of the node that represents the Environment - a reference to an environmental
   * parameter.
   */
  public final static String ENVIRONMENT_NODE = "Environment";

  /**
   * This is the name of the attribute telling the name of the environmental parameter.
   */
  public final static String PARAMETER_ATTRIBUTE = "Parameter";

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

  protected String type;
  protected String parameter_name;

  protected EnvironmentNode() {}

  /**
   * This constructor builds an EnvironmentNode given the XMLPolicyParser and 
   * the set of attributes of the XML element. It expects that a 
   * issrg.pba.rbac.xmlpolicy.XMLTags.TYPE_ATTRIBUTE and 
   * PARAMETER_ATTRIBUTE ("Type" and "Parameter") are 
   * present in this XML element. The value is converted from string into a
   * Java object using the Types.construct() method at runtime, so the type of 
   * the value
   * must be registered there.
   *
   * @param p - the XMLPolicyParser that builds this EnvironmentNode
   * @param attr - the attributes of this XML element
   * @see Types#construct
   */
  public EnvironmentNode(issrg.pba.rbac.xmlpolicy.XMLPolicyParser p, org.xml.sax.Attributes attr) throws issrg.pba.rbac.PolicyParsingException{
    super(ENVIRONMENT_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 "+ENVIRONMENT_NODE);
    parameter_name=(String)getAttributes().get(PARAMETER_ATTRIBUTE);
    if (parameter_name==null) throw new issrg.pba.rbac.PolicyParsingException(PARAMETER_ATTRIBUTE+" attribute was expected in "+ENVIRONMENT_NODE);
  }

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

  /**
   * This method evaluates the environmental parameter, as it is at run-time.
   * It looks for the environmental parameter in the Environment by its name,
   * as determined at construction time. If the value is of type other than
   * issrg.pba.rbac.Argument, then it is the result of this method; otherwise
   * the String value of the issrg.pba.rbac.Argument is extracted and decoded
   * into a Java object using Types.construct method.
   *
   * @param env - the Environment with the variables in it indexed by their
   *   name
   *
   * @return Object of type guaranteed by getType() method
   *
   * @throws EvaluationException, if there is no variable in the Environment
   *   with the expected name, or if its type is not the expected type, or if
   *   Types.construct failed to decode the value from String (no decoder 
   *   registered or other decoding problem)
   *
   * @see Types#construct
   */
  public Object evaluate(Environment env) throws EvaluationException{
    try{
      Object o = env.getEnv().get(parameter_name);
      if (o instanceof issrg.pba.rbac.Argument){
        issrg.pba.rbac.Argument arg = (issrg.pba.rbac.Argument)o;

        if (arg==null || arg.getType().intern()!=type){
          throw new EvaluationException("No such variable in the environment: "+parameter_name+" of type "+type);
        }

        return Types.construct(type, arg.getValue());
      }else{
        return o;
      }
    }catch (Throwable th){
      throw new EvaluationException("Evaluation run-time error", th);
    }
  }
}