JDOMXPath.java

/*--

 Copyright (C) 2000-2007 Jason Hunter & Brett McLaughlin.
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    derived from this software without prior written permission.  For
    written permission, please contact <request_AT_jdom_DOT_org>.

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    may "JDOM" appear in their name, without prior written permission
    from the JDOM Project Management <request_AT_jdom_DOT_org>.

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     "This product includes software developed by the
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 This software consists of voluntary contributions made by many
 individuals on behalf of the JDOM Project and was originally
 created by Jason Hunter <jhunter_AT_jdom_DOT_org> and
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 on the JDOM Project, please see <http://www.jdom.org/>.

 */

package org.jdom2.xpath.jaxen;


import java.util.*;

import org.jaxen.*;
import org.jdom2.*;


/**
 * A non-public concrete XPath implementation for Jaxen.
 *
 * @author  Laurent Bihanic
 */
public class JDOMXPath extends    org.jdom2.xpath.XPath {             // package protected

   /**
    * The compiled XPath object to select nodes.  This attribute can
    * not be made final as it needs to be set upon object
    * deserialization.
    */
   private transient JaxenXPath xPath;

   /**
    * The current context for XPath expression evaluation.
    */
   private           Object    currentContext;

   /**
    * Creates a new XPath wrapper object, compiling the specified
    * XPath expression.
    *
    * @param  expr   the XPath expression to wrap.
    *
    * @throws JDOMException   if the XPath expression is invalid.
    */
   public JDOMXPath(String expr) throws JDOMException {
      setXPath(expr);
   }

   /**
    * Evaluates the wrapped XPath expression and returns the list
    * of selected items.
    *
    * @param  context   the node to use as context for evaluating
    *                   the XPath expression.
    *
    * @return the list of selected items, which may be of types: {@link Element},
    *         {@link Attribute}, {@link Text}, {@link CDATA},
    *         {@link Comment}, {@link ProcessingInstruction}, Boolean,
    *         Double, or String.
    *
    * @throws JDOMException   if the evaluation of the XPath
    *                         expression on the specified context
    *                         failed.
    */
   public List<?> selectNodes(Object context) throws JDOMException {
      try {
         currentContext = context;

         return xPath.selectNodes(context);
      }
      catch (JaxenException ex1) {
         throw new JDOMException("XPath error while evaluating \"" +
                        xPath.toString() + "\": " + ex1.getMessage(), ex1);
      }
      finally {
         currentContext = null;
      }
   }

   /**
    * Evaluates the wrapped XPath expression and returns the first
    * entry in the list of selected nodes (or atomics).
    *
    * @param  context   the node to use as context for evaluating
    *                   the XPath expression.
    *
    * @return the first selected item, which may be of types: {@link Element},
    *         {@link Attribute}, {@link Text}, {@link CDATA},
    *         {@link Comment}, {@link ProcessingInstruction}, Boolean,
    *         Double, String, or <code>null</code> if no item was selected.
    *
    * @throws JDOMException   if the evaluation of the XPath
    *                         expression on the specified context
    *                         failed.
    */
   public Object selectSingleNode(Object context) throws JDOMException {
      try {
         currentContext = context;

         return xPath.selectSingleNode(context);
      }
      catch (JaxenException ex1) {
         throw new JDOMException("XPath error while evaluating \"" +
                        xPath.toString() + "\": " + ex1.getMessage(), ex1);
      }
      finally {
         currentContext = null;
      }
   }

   /**
    * Returns the string value of the first node selected by applying
    * the wrapped XPath expression to the given context.
    *
    * @param  context   the element to use as context for evaluating
    *                   the XPath expression.
    *
    * @return the string value of the first node selected by applying
    *         the wrapped XPath expression to the given context.
    *
    * @throws JDOMException   if the XPath expression is invalid or
    *                         its evaluation on the specified context
    *                         failed.
    */
   public String valueOf(Object context) throws JDOMException {
      try {
         currentContext = context;

         return xPath.stringValueOf(context);
      }
      catch (JaxenException ex1) {
         throw new JDOMException("XPath error while evaluating \"" +
                        xPath.toString() + "\": " + ex1.getMessage(), ex1);
      }
      finally {
         currentContext = null;
      }
   }

   /**
    * Returns the number value of the first item selected by applying
    * the wrapped XPath expression to the given context.
    *
    * @param  context   the element to use as context for evaluating
    *                   the XPath expression.
    *
    * @return the number value of the first item selected by applying
    *         the wrapped XPath expression to the given context,
    *         <code>null</code> if no node was selected or the
    *         special value {@link java.lang.Double#NaN}
    *         (Not-a-Number) if the selected value can not be
    *         converted into a number value.
    *
    * @throws JDOMException   if the XPath expression is invalid or
    *                         its evaluation on the specified context
    *                         failed.
    */
   public Number numberValueOf(Object context) throws JDOMException {
      try {
         currentContext = context;

         return xPath.numberValueOf(context);
      }
      catch (JaxenException ex1) {
         throw new JDOMException("XPath error while evaluating \"" +
                        xPath.toString() + "\": " + ex1.getMessage(), ex1);
      }
      finally {
         currentContext = null;
      }
   }

   /**
    * Defines an XPath variable and sets its value.
    *
    * @param  name    the variable name.
    * @param  value   the variable value.
    *
    * @throws IllegalArgumentException   if <code>name</code> is not
    *                                    a valid XPath variable name
    *                                    or if the value type is not
    *                                    supported by the underlying
    *                                    implementation
    */
   public void setVariable(String name, Object value)
                                        throws IllegalArgumentException {
      Object o = xPath.getVariableContext();
      if (o instanceof SimpleVariableContext) {
           ((SimpleVariableContext)o).setVariableValue(null, name, value);
      }
   }

   /**
    * Adds a namespace definition to the list of namespaces known of
    * this XPath expression.
    * <p>
    * <strong>Note</strong>: In XPath, there is no such thing as a
    * 'default namespace'.  The empty prefix <b>always</b> resolves
    * to the empty namespace URI.</p>
    *
    * @param  namespace   the namespace.
    */
   public void addNamespace(Namespace namespace) {
      try {
         xPath.addNamespace(namespace.getPrefix(), namespace.getURI());
      }
      catch (JaxenException ex1) { 
    	  /* Can't happen here. */ 
      }
   }

   /**
    * Returns the wrapped XPath expression as a string.
    *
    * @return the wrapped XPath expression as a string.
    */
   public String getXPath() {
      return (xPath.toString());
   }

   /**
    * Compiles and sets the XPath expression wrapped by this object.
    *
    * @param  expr   the XPath expression to wrap.
    *
    * @throws JDOMException   if the XPath expression is invalid.
    */
   private void setXPath(String expr) throws JDOMException {
      try {
         xPath = new JaxenXPath(expr);
         xPath.setNamespaceContext(new NSContext());
      }
      catch (Exception ex1) {
         throw new JDOMException(
                        "Invalid XPath expression: \"" + expr + "\"", ex1);
      }
   }

   public String toString() {
      return (xPath.toString());
   }

   public boolean equals(Object o) {
      if (o instanceof JDOMXPath) {
         JDOMXPath x = (JDOMXPath)o;

         return (super.equals(o) &&
                 xPath.toString().equals(x.xPath.toString()));
      }
      return false;
   }

   public int hashCode() {
      return xPath.hashCode();
   }

   private class NSContext extends SimpleNamespaceContext {
      public NSContext() {
         super();
      }

      /**
       * <i>[Jaxen NamespaceContext interface support]</i> Translates
       * the provided namespace prefix into the matching bound
       * namespace URI.
       *
       * @param  prefix   the namespace prefix to resolve.
       *
       * @return the namespace URI matching the prefix.
       */
      public String translateNamespacePrefixToUri(String prefix) {
         if ((prefix == null) || (prefix.length() == 0)) {
            return null;
         }

         String uri = super.translateNamespacePrefixToUri(prefix);
         if (uri == null) {
            Object ctx = currentContext;
            if (ctx != null) {
               Element elt = null;

               // Get closer element node
               if (ctx instanceof Element) {
                  elt = (Element)ctx;
               } else if (ctx instanceof Attribute) {
                  elt = ((Attribute)ctx).getParent();
               } else if (ctx instanceof Content) {
                  elt = ((Content) ctx).getParentElement();
               } else if (ctx instanceof Document) {
                  elt = ((Document)ctx).getRootElement();
               }

               if (elt != null) {
                  Namespace ns = elt.getNamespace(prefix);
                  if (ns != null) {
                     uri = ns.getURI();
                  }
               }
            }
         }
         return uri;
      }
   }
}