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  /*
   * $Id: XPath.java,v 1.8 2010-11-01 04:36:13 joehw Exp $
   * %W% %E%
   */
  package mf.javax.xml.xpath;
  
  import org.xml.sax.InputSource;
  
  import mf.javax.xml.namespace.NamespaceContext;
  import mf.javax.xml.namespace.QName;
  
  /**
   * <p><code>XPath</code> provides access to the XPath evaluation environment and expressions.</p>
   * <p/>
   * <a name="XPath-evaluation"/>
   * <table border="1" cellpadding="2">
   * <thead>
   * <tr>
   * <th colspan="2">Evaluation of XPath Expressions.</th>
   * </tr>
   * </thead>
   * <tbody>
   * <tr>
   * <td>context</td>
   * <td>
   * If a request is made to evaluate the expression in the absence
   * of a context item, an empty document node will be used for the context.
   * For the purposes of evaluating XPath expressions, a DocumentFragment
   * is treated like a Document node.
   * </td>
   * </tr>
   * <tr>
   * <td>variables</td>
   * <td>
   * If the expression contains a variable reference, its value will be found through the {@link XPathVariableResolver}
   * set with {@link #setXPathVariableResolver(XPathVariableResolver resolver)}.
   * An {@link XPathExpressionException} is raised if the variable resolver is undefined or
   * the resolver returns <code>null</code> for the variable.
   * The value of a variable must be immutable through the course of any single evaluation.</p>
   * </td>
   * </tr>
   * <tr>
   * <td>functions</td>
   * <td>
   * If the expression contains a function reference, the function will be found through the {@link XPathFunctionResolver}
   * set with {@link #setXPathFunctionResolver(XPathFunctionResolver resolver)}.
   * An {@link XPathExpressionException} is raised if the function resolver is undefined or
   * the function resolver returns <code>null</code> for the function.</p>
   * </td>
   * </tr>
   * <tr>
   * <td>QNames</td>
   * <td>
   * QNames in the expression are resolved against the XPath namespace context
   * set with {@link #setNamespaceContext(NamespaceContext nsContext)}.
   * </td>
   * </tr>
   * <tr>
   * <td>result</td>
   * <td>
   * This result of evaluating an expression is converted to an instance of the desired return type.
   * Valid return types are defined in {@link XPathConstants}.
   * Conversion to the return type follows XPath conversion rules.</p>
   * </td>
   * </tr>
   * </table>
   * <p/>
   * <p>An XPath object is not thread-safe and not reentrant.
   * In other words, it is the application's responsibility to make
   * sure that one {@link XPath} object is not used from
   * more than one thread at any given time, and while the <code>evaluate</code>
   * method is invoked, applications may not recursively call
   * the <code>evaluate</code> method.
   * <p/>
   *
   * @author <a href="Norman.Walsh@Sun.com">Norman Walsh</a>
   * @author <a href="Jeff.Suttor@Sun.com">Jeff Suttor</a>
   * @version $Revision: 1.8 $, $Date: 2010-11-01 04:36:13 $
   * @see <a href="http://www.w3.org/TR/xpath">XML Path Language (XPath) Version 1.0</a>
   * @since 1.5
   */
  public interface XPath {
  
      /**
       * <p>Reset this <code>XPath</code> to its original configuration.</p>
       * <p/>
       * <p><code>XPath</code> is reset to the same state as when it was created with
       * {@link XPathFactory#newXPath()}.
       * <code>reset()</code> is designed to allow the reuse of existing <code>XPath</code>s
       * thus saving resources associated with the creation of new <code>XPath</code>s.</p>
       * <p/>
       * <p>The reset <code>XPath</code> is not guaranteed to have the same {@link XPathFunctionResolver}, {@link XPathVariableResolver}
       * or {@link NamespaceContext} <code>Object</code>s, e.g. {@link Object#equals(Object obj)}.
       * It is guaranteed to have a functionally equal <code>XPathFunctionResolver</code>, <code>XPathVariableResolver</code>
       * and <code>NamespaceContext</code>.</p>
       */
      void reset();
  
      /**
       * <p>Return the current variable resolver.</p>
       * <p/>
       * <p><code>null</code> is returned in no variable resolver is in effect.</p>
       *
       * @return Current variable resolver.
       */
      XPathVariableResolver getXPathVariableResolver();
  
      /**
       * <p>Establish a variable resolver.</p>
       * <p/>
       * <p>A <code>NullPointerException</code> is thrown if <code>resolver</code> is <code>null</code>.</p>
       *
       * @param resolver Variable resolver.
       * @throws NullPointerException If <code>resolver</code> is <code>null</code>.
       */
      void setXPathVariableResolver(XPathVariableResolver resolver);
  
      /**
       * <p>Return the current function resolver.</p>
       * <p/>
       * <p><code>null</code> is returned in no function resolver is in effect.</p>
       *
       * @return Current function resolver.
       */
      XPathFunctionResolver getXPathFunctionResolver();
  
      /**
       * <p>Establish a function resolver.</p>
       * <p/>
       * <p>A <code>NullPointerException</code> is thrown if <code>resolver</code> is <code>null</code>.</p>
       *
       * @param resolver XPath function resolver.
       * @throws NullPointerException If <code>resolver</code> is <code>null</code>.
       */
      void setXPathFunctionResolver(XPathFunctionResolver resolver);
  
      /**
       * <p>Return the current namespace context.</p>
       * <p/>
       * <p><code>null</code> is returned in no namespace context is in effect.</p>
       *
       * @return Current Namespace context.
       */
      NamespaceContext getNamespaceContext();
  
      /**
       * <p>Establish a namespace context.</p>
       * <p/>
       * <p>A <code>NullPointerException</code> is thrown if <code>nsContext</code> is <code>null</code>.</p>
       *
       * @param nsContext Namespace context to use.
       * @throws NullPointerException If <code>nsContext</code> is <code>null</code>.
       */
      void setNamespaceContext(NamespaceContext nsContext);
  
      /**
       * <p>Compile an XPath expression for later evaluation.</p>
       * <p/>
       * <p>If <code>expression</code> contains any {@link XPathFunction}s,
       * they must be available via the {@link XPathFunctionResolver}.
       * An {@link XPathExpressionException} will be thrown if the
       * <code>XPathFunction</code>
       * cannot be resovled with the <code>XPathFunctionResolver</code>.</p>
       * <p/>
       * <p>If <code>expression</code> contains any variables, the
       * {@link XPathVariableResolver} in effect
       * <strong>at compile time</strong> will be used to resolve them.</p>
       * <p/>
       * <p>If <code>expression</code> is <code>null</code>, a <code>NullPointerException</code> is thrown.</p>
       *
       * @param expression The XPath expression.
       * @return Compiled XPath expression.
       * @throws XPathExpressionException If <code>expression</code> cannot be compiled.
       * @throws NullPointerException     If <code>expression</code> is <code>null</code>.
       */
      XPathExpression compile(String expression)
              throws XPathExpressionException;
  
      /**
       * <p>Evaluate an <code>XPath</code> expression in the specified context and return the result as the specified type.</p>
       * <p/>
       * <p>See <a href="#XPath-evaluation">Evaluation of XPath Expressions</a> for context item evaluation,
       * variable, function and <code>QName</code> resolution and return type conversion.</p>
       * <p/>
       * <p>If <code>returnType</code> is not one of the types defined in {@link XPathConstants} (
       * {@link XPathConstants#NUMBER NUMBER},
       * {@link XPathConstants#STRING STRING},
       * {@link XPathConstants#BOOLEAN BOOLEAN},
       * {@link XPathConstants#NODE NODE} or
       * {@link XPathConstants#NODESET NODESET})
       * then an <code>IllegalArgumentException</code> is thrown.</p>
       * <p/>
       * <p>If a <code>null</code> value is provided for
       * <code>item</code>, an empty document will be used for the
       * context.
       * If <code>expression</code> or <code>returnType</code> is <code>null</code>, then a
       * <code>NullPointerException</code> is thrown.</p>
       *
       * @param expression The XPath expression.
       * @param item       The starting context (a node, for example).
       * @param returnType The desired return type.
       * @return Result of evaluating an XPath expression as an <code>Object</code> of <code>returnType</code>.
       * @throws XPathExpressionException If <code>expression</code> cannot be evaluated.
       * @throws IllegalArgumentException If <code>returnType</code> is not one of the types defined in {@link XPathConstants}.
       * @throws NullPointerException     If <code>expression</code> or <code>returnType</code> is <code>null</code>.
       */
      Object evaluate(String expression, Object item, QName returnType)
              throws XPathExpressionException;
  
      /**
       * <p>Evaluate an XPath expression in the specified context and return the result as a <code>String</code>.</p>
       * <p/>
       * <p>This method calls {@link #evaluate(String expression, Object item, QName returnType)} with a <code>returnType</code> of
       * {@link XPathConstants#STRING}.</p>
       * <p/>
       * <p>See <a href="#XPath-evaluation">Evaluation of XPath Expressions</a> for context item evaluation,
       * variable, function and QName resolution and return type conversion.</p>
       * <p/>
       * <p>If a <code>null</code> value is provided for
       * <code>item</code>, an empty document will be used for the
       * context.
       * If <code>expression</code> is <code>null</code>, then a <code>NullPointerException</code> is thrown.</p>
       *
       * @param expression The XPath expression.
       * @param item       The starting context (a node, for example).
       * @return The <code>String</code> that is the result of evaluating the expression and
       * converting the result to a <code>String</code>.
       * @throws XPathExpressionException If <code>expression</code> cannot be evaluated.
       * @throws NullPointerException     If <code>expression</code> is <code>null</code>.
       */
      String evaluate(String expression, Object item)
              throws XPathExpressionException;
  
      /**
       * <p>Evaluate an XPath expression in the context of the specified <code>InputSource</code>
       * and return the result as the specified type.</p>
       * <p/>
       * <p>This method builds a data model for the {@link InputSource} and calls
       * {@link #evaluate(String expression, Object item, QName returnType)} on the resulting document object.</p>
       * <p/>
       * <p>See <a href="#XPath-evaluation">Evaluation of XPath Expressions</a> for context item evaluation,
       * variable, function and QName resolution and return type conversion.</p>
       * <p/>
       * <p>If <code>returnType</code> is not one of the types defined in {@link XPathConstants},
       * then an <code>IllegalArgumentException</code> is thrown.</p>
       * <p/>
       * <p>If <code>expression</code>, <code>source</code> or <code>returnType</code> is <code>null</code>,
       * then a <code>NullPointerException</code> is thrown.</p>
       *
       * @param expression The XPath expression.
       * @param source     The input source of the document to evaluate over.
       * @param returnType The desired return type.
       * @return The <code>Object</code> that encapsulates the result of evaluating the expression.
       * @throws XPathExpressionException If expression cannot be evaluated.
       * @throws IllegalArgumentException If <code>returnType</code> is not one of the types defined in {@link XPathConstants}.
       * @throws NullPointerException     If <code>expression</code>, <code>source</code> or <code>returnType</code>
       *                                  is <code>null</code>.
       */
      Object evaluate(
              String expression,
              InputSource source,
              QName returnType)
              throws XPathExpressionException;
  
      /**
       * <p>Evaluate an XPath expression in the context of the specified <code>InputSource</code>
       * and return the result as a <code>String</code>.</p>
       * <p/>
       * <p>This method calls {@link #evaluate(String expression, InputSource source, QName returnType)} with a
       * <code>returnType</code> of {@link XPathConstants#STRING}.</p>
       * <p/>
       * <p>See <a href="#XPath-evaluation">Evaluation of XPath Expressions</a> for context item evaluation,
       * variable, function and QName resolution and return type conversion.</p>
       * <p/>
       * <p>If <code>expression</code> or <code>source</code> is <code>null</code>,
       * then a <code>NullPointerException</code> is thrown.</p>
       *
       * @param expression The XPath expression.
       * @param source     The <code>InputSource</code> of the document to evaluate over.
       * @return The <code>String</code> that is the result of evaluating the expression and
       * converting the result to a <code>String</code>.
       * @throws XPathExpressionException If expression cannot be evaluated.
       * @throws NullPointerException     If <code>expression</code> or <code>source</code> is <code>null</code>.
       */
      String evaluate(String expression, InputSource source)
              throws XPathExpressionException;
  }
  