types.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.
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* list of conditions and the following disclaimer.
* 
* Redistributions in binary form must reproduce the above copyright notice, 
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* and/or other materials provided with the distribution. 
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* 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" 
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package issrg.pba.rbac.xmlpolicy.ifstatement;

/**
 * This class maintains a registry of known types, so that the string encoding
 * of the values of these types can be decoded from the XML Policy. When 
 * registering the type, the impelementing class should have a constructor with
 * a single String parameter to it.
 *
 * <p>By default there are three types known: BOOLEAN_TYPE, INTEGER_TYPE and
 * STRING_TYPE ("Boolean", "Integer" and "String" respectively).
 *
 * @author A.Otenko
 */

public final class Types {
  protected final static java.util.Map knownTypes=new java.util.Hashtable();

  public final static String INTEGER_TYPE = "Integer";
  public final static String BOOLEAN_TYPE = "Boolean";
  public final static String STRING_TYPE = "String";

  static{
    registerType(INTEGER_TYPE, Integer.class);
    registerType(BOOLEAN_TYPE, Boolean.class);
    registerType(STRING_TYPE, String.class);
  }

  /**
   * This method registers a class to be used to instantiate values of the
   * given type from String encoding.
   *
   * @param type - the type of the value
   * @param c - the Class that represents the values of that type; it must
   *   have a public constructor with a single String argument
   */
  public static void registerType(String type, Class c){
    try{
      knownTypes.put(type, c.getConstructor(new Class[]{String.class}));
    }catch (NoSuchMethodException nsme){
      nsme.printStackTrace();
    }
  }

  /**
   * This is the method for building the objects of known types out of their 
   * String encoding.
   *
   * @param type is the type of the object, as it appears in the XML Policy
   * @param value is the String encoding of the object
   *
   * @return the constructed type-specific Object
   *
   * @throws EvaluationException if the constructor is not found or the value 
   *    is not
   *    properly encoded
   */
  public static Object construct(String type, String value) throws EvaluationException{
    try{
      java.lang.reflect.Constructor c = (java.lang.reflect.Constructor)(knownTypes.get(type));
      if (c==null) throw new EvaluationException("Could not build a value of type "+type+" out of \""+value+"\": no implementing Class found for this type");

      return c.newInstance(new Object[]{value});
    }catch (Throwable th){
      throw new EvaluationException("Could not build a value of type "+type+" out of \""+value+"\"", th);
    }
  }
}