src/org/apache/xpath/Expression.java

/*
 * The Apache Software License, Version 1.1
 *
 *
 * Copyright (c) 1999 The Apache Software Foundation.  All rights 
 * reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer. 
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * 3. The end-user documentation included with the redistribution,
 *    if any, must include the following acknowledgment:  
 *       "This product includes software developed by the
 *        Apache Software Foundation (http://www.apache.org/)."
 *    Alternately, this acknowledgment may appear in the software itself,
 *    if and wherever such third-party acknowledgments normally appear.
 *
 * 4. The names "Xalan" and "Apache Software Foundation" must
 *    not be used to endorse or promote products derived from this
 *    software without prior written permission. For written 
 *    permission, please contact apache@apache.org.
 *
 * 5. Products derived from this software may not be called "Apache",
 *    nor may "Apache" appear in their name, without prior written
 *    permission of the Apache Software Foundation.
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
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 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation and was
 * originally based on software copyright (c) 1999, Lotus
 * Development Corporation., http://www.lotus.com.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 */
package org.apache.xpath;

//import org.w3c.dom.Node;

import org.apache.xpath.objects.XObject;
import org.apache.xpath.res.XPATHErrorResources;
import org.apache.xalan.res.XSLMessages;

import org.xml.sax.XMLReader;

import javax.xml.transform.TransformerConfigurationException;
import javax.xml.transform.TransformerException;

import org.apache.xml.utils.SAXSourceLocator;

import javax.xml.transform.SourceLocator;
import javax.xml.transform.ErrorListener;

/**
 * This abstract class serves as the base for all expression objects.  An
 * Expression can be executed to return a {@link org.apache.xpath.objects.XObject},
 * normally has a location within a document or DOM, can send error and warning
 * events, and normally do not hold state and are meant to be immutable once
 * construction has completed.  An exception to the immutibility rule is iterators
 * and walkers, which must be cloned in order to be used -- the original must
 * still be immutable.
 */
public abstract class Expression implements java.io.Serializable
{

  /**
   * The location where this expression was built from.  Need for diagnostic
   *  messages. May be null.
   *  @serial
   */
  protected SourceLocator m_slocator;
  
  /**
   * Tell if this expression or it's subexpressions can traverse outside 
   * the current subtree.
   * 
   * @return true if traversal outside the context node's subtree can occur.
   */
   public boolean canTraverseOutsideSubtree()
   {
    return false;
   }

  /**
   * Set the location where this expression was built from.
   *
   *
   * @param locator the location where this expression was built from, may be 
   *                null.
   */
  public void setSourceLocator(SourceLocator locator)
  {
    m_slocator = locator;
  }

  /**
   * Execute an expression in the XPath runtime context, and return the 
   * result of the expression.
   *
   *
   * @param xctxt The XPath runtime context.
   *
   * @return The result of the expression in the form of a <code>XObject</code>.
   *
   * @throws javax.xml.transform.TransformerException if a runtime exception 
   *         occurs.
   */
  public abstract XObject execute(XPathContext xctxt)
    throws javax.xml.transform.TransformerException;

  /**
   * Warn the user of an problem.
   *
   * @param xctxt The XPath runtime context.
   * @param msg An error number that corresponds to one of the numbers found 
   *            in {@link org.apache.xpath.res.XPATHErrorResources}, which is 
   *            a key for a format string.
   * @param args An array of arguments represented in the format string, which 
   *             may be null.
   *
   * @throws TransformerException if the current ErrorListoner determines to 
   *                              throw an exception.
   */
  public void warn(XPathContext xctxt, int msg, Object[] args)
          throws javax.xml.transform.TransformerException
  {

    java.lang.String fmsg = XSLMessages.createXPATHWarning(msg, args);

    if (null != xctxt)
    {
      ErrorListener eh = xctxt.getErrorListener();

      // TO DO: Need to get stylesheet Locator from here.
      eh.warning(new TransformerException(fmsg, xctxt.getSAXLocator()));
    }
  }

  /**
   * Tell the user of an assertion error, and probably throw an
   * exception.
   *
   * @param b  If false, a runtime exception will be thrown.
   * @param msg The assertion message, which should be informative.
   * 
   * @throws RuntimeException if the b argument is false.
   */
  public void assertion(boolean b, java.lang.String msg)
          throws javax.xml.transform.TransformerException
  {

    if (!b)
    {
      java.lang.String fMsg = XSLMessages.createXPATHMessage(
        XPATHErrorResources.ER_INCORRECT_PROGRAMMER_ASSERTION,
        new Object[]{ msg });

      throw new RuntimeException(fMsg);
    }
  }

  /**
   * Tell the user of an error, and probably throw an
   * exception.
   *
   * @param xctxt The XPath runtime context.
   * @param msg An error number that corresponds to one of the numbers found 
   *            in {@link org.apache.xpath.res.XPATHErrorResources}, which is 
   *            a key for a format string.
   * @param args An array of arguments represented in the format string, which 
   *             may be null.
   *
   * @throws TransformerException if the current ErrorListoner determines to 
   *                              throw an exception.
   */
  public void error(XPathContext xctxt, int msg, Object[] args)
          throws javax.xml.transform.TransformerException
  {

    java.lang.String fmsg = XSLMessages.createXPATHMessage(msg, args);

    if (null != xctxt)
    {
      ErrorListener eh = xctxt.getErrorListener();
      TransformerException te = new TransformerException(fmsg, m_slocator);

      eh.fatalError(te);
    }
  }
}