interpreter.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;

/**
 * This is the interface to an interpreter of the evaluation operation. 
 * Implementations
 * of this class are expected to be provided by the AEF/PEP at run-time. The 
 * implementations
 * would tell what kind of terms they can interpret to complete the operation 
 * with a definite
 * result. If the interpreter can evaluate an expression, it returns the 
 * resulting type of the
 * expression, when canEvaluate method is invoked, and the evaluation result or 
 * an EvaluationException
 * when an evaluate method is invoked.
 *
 * @author A.Otenko
 */

public interface Interpreter {
  /**
   * This method returns the string type of the result of evaluating the given
   * set of Terms, or null, if the expression cannot be evaluated by this 
   * interpreter.
   *
   * @param t - the array of Terms; can be null and can be empty
   *
   * @return the String name of the type of the result, or null, if the 
   *   expression cannot be evaluated
   */
  public String canEvaluate(Term [] t);

  /**
   * This method evaluates the expression given the environment.
   *
   * @param env - the Environment with variables used in IF-statement
   * @param t - the sequence of Terms in the order that they appear in the 
   *   policy; can be null or an empty array
   *
   * @return the object of the type guaranteed by canEvaluate method; never null
   *
   * @throws EvaluationException, if for some reason evaluation failed
   */
  public Object evaluate(Environment env, Term [] t) throws EvaluationException;
}