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Xalan-Java is an XSLT processor for transforming XML documents into HTML, text, or other XML document types. It implements XSL Transformations (XSLT) Version 1.0 and XML Path Language (XPath) Version 1.0 and can be used from the command line, in an applet or a servlet, or as a module in other program.
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/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements. See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership. The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the  "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
/*
 * $Id: ExtensionHandler.java 468637 2006-10-28 06:51:02Z minchau $
 */
package org.apache.xalan.extensions;

import java.io.IOException;
import java.util.Vector;

import javax.xml.transform.TransformerException;

import org.apache.xalan.templates.ElemTemplateElement;
import org.apache.xalan.templates.Stylesheet;
import org.apache.xalan.transformer.TransformerImpl;
import org.apache.xpath.functions.FuncExtFunction;

/**
 * Abstract base class for handling an extension namespace for XPath.
 * Provides functions to test a function's existence and call a function.
 * Also provides functions for calling an element and testing for
 * an element's existence.
 *
 * @author Sanjiva Weerawarana ([email protected])
 * @xsl.usage internal
 */
public abstract class ExtensionHandler
{

  /** uri of the extension namespace */
  protected String m_namespaceUri; 

  /** scripting language of implementation */
  protected String m_scriptLang;

  /**
   * This method loads a class using the context class loader if we're
   * running under Java2 or higher.
   * 
   * @param className Name of the class to load
   */
  static Class getClassForName(String className)
      throws ClassNotFoundException
  {
    // Hack for backwards compatibility with XalanJ1 stylesheets
    if(className.equals("org.apache.xalan.xslt.extensions.Redirect")) {
      className = "org.apache.xalan.lib.Redirect";
    }

    return ObjectFactory.findProviderClass(
        className, ObjectFactory.findClassLoader(), true);
  }

  /**
   * Construct a new extension namespace handler given all the information
   * needed.
   *
   * @param namespaceUri the extension namespace URI that I'm implementing
   * @param scriptLang   language of code implementing the extension
   */
  protected ExtensionHandler(String namespaceUri, String scriptLang)
  {
    m_namespaceUri = namespaceUri;
    m_scriptLang = scriptLang;
  }

  /**
   * Tests whether a certain function name is known within this namespace.
   * @param function name of the function being tested
   * @return true if its known, false if not.
   */
  public abstract boolean isFunctionAvailable(String function);

  /**
   * Tests whether a certain element name is known within this namespace.
   * @param element Name of element to check
   * @return true if its known, false if not.
   */
  public abstract boolean isElementAvailable(String element);

  /**
   * Process a call to a function.
   *
   * @param funcName Function name.
   * @param args     The arguments of the function call.
   * @param methodKey A key that uniquely identifies this class and method call.
   * @param exprContext The context in which this expression is being executed.
   *
   * @return the return value of the function evaluation.
   *
   * @throws TransformerException          if parsing trouble
   */
  public abstract Object callFunction(
    String funcName, Vector args, Object methodKey,
      ExpressionContext exprContext) throws TransformerException;

  /**
   * Process a call to a function.
   *
   * @param extFunction The XPath extension function.
   * @param args     The arguments of the function call.
   * @param exprContext The context in which this expression is being executed.
   *
   * @return the return value of the function evaluation.
   *
   * @throws TransformerException          if parsing trouble
   */
  public abstract Object callFunction(
    FuncExtFunction extFunction, Vector args,
      ExpressionContext exprContext) throws TransformerException;

  /**
   * Process a call to this extension namespace via an element. As a side
   * effect, the results are sent to the TransformerImpl's result tree.
   *
   * @param localPart      Element name's local part.
   * @param element        The extension element being processed.
   * @param transformer    Handle to TransformerImpl.
   * @param stylesheetTree The compiled stylesheet tree.
   * @param methodKey      A key that uniquely identifies this class and method call.
   *
   * @throws XSLProcessorException thrown if something goes wrong
   *            while running the extension handler.
   * @throws MalformedURLException if loading trouble
   * @throws FileNotFoundException if loading trouble
   * @throws IOException           if loading trouble
   * @throws TransformerException  if parsing trouble
   */
  public abstract void processElement(
    String localPart, ElemTemplateElement element, TransformerImpl transformer,
      Stylesheet stylesheetTree, Object methodKey) throws TransformerException, IOException;
}