code: /*
   * 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.
   */
  // $Id$
  
  package org.apache.xpath.jaxp;
  
  import javax.xml.namespace.QName;
  import javax.xml.parsers.DocumentBuilder;
  import javax.xml.parsers.DocumentBuilderFactory;
  import javax.xml.xpath.XPathConstants;
  import javax.xml.xpath.XPathExpressionException;
  import javax.xml.xpath.XPathFunctionResolver;
  import javax.xml.xpath.XPathVariableResolver;
  
  import org.apache.xalan.res.XSLMessages;
  import org.apache.xpath.objects.XObject;
  import org.apache.xpath.res.XPATHErrorResources;
  import org.w3c.dom.DOMImplementation;
  import org.w3c.dom.Document;
  import org.w3c.dom.Node;
  import org.w3c.dom.traversal.NodeIterator;
  import org.xml.sax.InputSource;
  
  /**
   * The XPathExpression interface encapsulates a (compiled) XPath expression.
   *
   * @version $Revision$
   * @author  Ramesh Mandava
   */
  public class XPathExpressionImpl  implements javax.xml.xpath.XPathExpression{
  
      private XPathFunctionResolver functionResolver;
      private XPathVariableResolver variableResolver;
      private JAXPPrefixResolver prefixResolver;
      private org.apache.xpath.XPath xpath;
  
      // By default Extension Functions are allowed in XPath Expressions. If
      // Secure Processing Feature is set on XPathFactory then the invocation of
      // extensions function need to throw XPathFunctionException
      private boolean featureSecureProcessing = false;
  
      /** Protected constructor to prevent direct instantiation; use compile()
       * from the context.
       */
      protected XPathExpressionImpl() { };
  
      protected XPathExpressionImpl(org.apache.xpath.XPath xpath, 
              JAXPPrefixResolver prefixResolver, 
              XPathFunctionResolver functionResolver,
              XPathVariableResolver variableResolver ) { 
          this.xpath = xpath;
          this.prefixResolver = prefixResolver;
          this.functionResolver = functionResolver;
          this.variableResolver = variableResolver;
          this.featureSecureProcessing = false;
      };
  
      protected XPathExpressionImpl(org.apache.xpath.XPath xpath,
              JAXPPrefixResolver prefixResolver,
              XPathFunctionResolver functionResolver,
              XPathVariableResolver variableResolver,
              boolean featureSecureProcessing ) { 
          this.xpath = xpath;
          this.prefixResolver = prefixResolver;
          this.functionResolver = functionResolver;
          this.variableResolver = variableResolver;
          this.featureSecureProcessing = featureSecureProcessing;
      };
  
      public void setXPath (org.apache.xpath.XPath xpath ) {
          this.xpath = xpath;
      }  
  
      public Object eval(Object item, QName returnType)
              throws javax.xml.transform.TransformerException {
          XObject resultObject = eval ( item );
          return getResultAsType( resultObject, returnType );
      }
      
      private XObject eval ( Object contextItem )
              throws javax.xml.transform.TransformerException {
          org.apache.xpath.XPathContext xpathSupport = null;
  
          // Create an XPathContext that doesn't support pushing and popping of
          // variable resolution scopes.  Sufficient for simple XPath 1.0
          // expressions.
          if ( functionResolver != null ) {
              JAXPExtensionsProvider jep = new JAXPExtensionsProvider(
                      functionResolver, featureSecureProcessing );
              xpathSupport = new org.apache.xpath.XPathContext(jep, false);
          } else {
              xpathSupport = new org.apache.xpath.XPathContext(false);
          }
  
          xpathSupport.setVarStack(new JAXPVariableStack(variableResolver));
          XObject xobj = null;
            
          Node contextNode = (Node)contextItem;
          // We always need to have a ContextNode with Xalan XPath implementation
          // To allow simple expression evaluation like 1+1 we are setting 
          // dummy Document as Context Node
          if ( contextNode == null ) {
                contextNode = getDummyDocument();
          } 
  
          xobj = xpath.execute(xpathSupport, contextNode, prefixResolver );
          return xobj;
      }
  
  
      /**
       * <p>Evaluate the compiled XPath expression in the specified context and
       *  return the result as the specified type.</p>
       *
       * <p>See "Evaluation of XPath Expressions" section of JAXP 1.3 spec
       * for context item evaluation,
       * variable, function and QName resolution and return type conversion.</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>If a <code>null</code> value is provided for
       * <code>item</code>, an empty document will be used for the
       * context.
       * If <code>returnType</code> is <code>null</code>, then a 
       * <code>NullPointerException</code> is thrown.</p>
       *
       * @param item The starting context (node or node list, for example).
       * @param returnType The desired return type.
       *
       * @return The <code>Object</code> that is the result of evaluating the
       * expression and converting the result to
       *   <code>returnType</code>.
       *
       * @throws XPathExpressionException If the expression cannot be evaluated.
       * @throws IllegalArgumentException If <code>returnType</code> is not one
       * of the types defined in {@link XPathConstants}.
       * @throws NullPointerException If  <code>returnType</code> is
       * <code>null</code>.
       */
      public Object evaluate(Object item, QName returnType)
          throws XPathExpressionException {
          //Validating parameters to enforce constraints defined by JAXP spec
          if ( returnType == null ) {
             //Throwing NullPointerException as defined in spec
              String fmsg = XSLMessages.createXPATHMessage( 
                      XPATHErrorResources.ER_ARG_CANNOT_BE_NULL,
                      new Object[] {"returnType"} );
              throw new NullPointerException( fmsg );
          }
          // Checking if requested returnType is supported. returnType need to be
          // defined in XPathConstants 
          if ( !isSupported ( returnType ) ) {
              String fmsg = XSLMessages.createXPATHMessage( 
                      XPATHErrorResources.ER_UNSUPPORTED_RETURN_TYPE,
                      new Object[] { returnType.toString() } );
              throw new IllegalArgumentException ( fmsg );
          }
          try { 
              return eval( item, returnType);
          } catch ( java.lang.NullPointerException npe ) {
              // If VariableResolver returns null Or if we get 
              // NullPointerException at this stage for some other reason
              // then we have to reurn XPathException
              throw new XPathExpressionException ( npe );
          } catch ( javax.xml.transform.TransformerException te ) {
              Throwable nestedException = te.getException();
              if ( nestedException instanceof javax.xml.xpath.XPathFunctionException ) {
                  throw (javax.xml.xpath.XPathFunctionException)nestedException;
              } else {
                  // For any other exceptions we need to throw
                  // XPathExpressionException ( as per spec )
                  throw new XPathExpressionException( te);
              }
          }
  
      }
      
      /**
       * <p>Evaluate the compiled XPath expression in the specified context and
       * return the result as a <code>String</code>.</p>
       *
       * <p>This method calls {@link #evaluate(Object item, QName returnType)}
       * with a <code>returnType</code> of
       * {@link XPathConstants#STRING}.</p>
       *
       * <p>See "Evaluation of XPath Expressions" section of JAXP 1.3 spec
       *  for context item evaluation,
       * variable, function and QName resolution and return type conversion.</p>
       *
       * <p>If a <code>null</code> value is provided for
       * <code>item</code>, an empty document will be used for the
       * context.
       *
       * @param item The starting context (node or node list, 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 the expression cannot be evaluated.
       */
      public String evaluate(Object item) 
          throws XPathExpressionException {
          return (String)this.evaluate( item, XPathConstants.STRING );
      }
  
  
  
      static DocumentBuilderFactory dbf = null;
      static DocumentBuilder db = null;
      static Document d = null;
  
      /**
       * <p>Evaluate the compiled XPath expression in the context of the 
       * specified <code>InputSource</code> and return the result as the
       *  specified type.</p>
       *
       * <p>This method builds a data model for the {@link InputSource} and calls
       * {@link #evaluate(Object item, QName returnType)} on the resulting 
       * document object.</p>
       *
       * <p>See "Evaluation of XPath Expressions" section of JAXP 1.3 spec
       *  for context item evaluation,
       * variable, function and QName resolution and return type conversion.</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>If <code>source</code> or <code>returnType</code> is <code>null</code>,
       * then a <code>NullPointerException</code> is thrown.</p>
       *
       * @param source The <code>InputSource</code> of the document to evaluate
       * over.
       * @param returnType The desired return type.
       *
       * @return The <code>Object</code> that is the result of evaluating the
       * expression and converting the result to
       *   <code>returnType</code>.
       *
       * @throws XPathExpressionException If the expression cannot be evaluated.
       * @throws IllegalArgumentException If <code>returnType</code> is not one
       * of the types defined in {@link XPathConstants}.
       * @throws NullPointerException If  <code>source</code> or 
       * <code>returnType</code> is <code>null</code>.
       */
      public Object evaluate(InputSource source, QName returnType)
          throws XPathExpressionException {
          if ( ( source == null ) || ( returnType == null ) ) {
              String fmsg = XSLMessages.createXPATHMessage( 
                      XPATHErrorResources.ER_SOURCE_RETURN_TYPE_CANNOT_BE_NULL,
                      null );
              throw new NullPointerException ( fmsg );
          }
          // Checking if requested returnType is supported. returnType need to be
          // defined in XPathConstants 
          if ( !isSupported ( returnType ) ) {
              String fmsg = XSLMessages.createXPATHMessage( 
                      XPATHErrorResources.ER_UNSUPPORTED_RETURN_TYPE,
                      new Object[] { returnType.toString() } );
              throw new IllegalArgumentException ( fmsg );
          }
          try {
              if ( dbf == null ) {
                  dbf = DocumentBuilderFactory.newInstance();
                  dbf.setNamespaceAware( true );
                  dbf.setValidating( false );
              }
              db = dbf.newDocumentBuilder();
              Document document = db.parse( source );
              return eval(  document, returnType );
          } catch ( Exception e ) {
              throw new XPathExpressionException ( e );
          }
      }
  
      /**
       * <p>Evaluate the compiled XPath expression in the context of the specified <code>InputSource</code> and return the result as a
       * <code>String</code>.</p>
       *
       * <p>This method calls {@link #evaluate(InputSource source, QName returnType)} with a <code>returnType</code> of
       * {@link XPathConstants#STRING}.</p>
       *
       * <p>See "Evaluation of XPath Expressions" section of JAXP 1.3 spec
       * for context item evaluation,
       * variable, function and QName resolution and return type conversion.</p>
       *
       * <p>If <code>source</code> is <code>null</code>, then a <code>NullPointerException</code> is thrown.</p>
       *
       * @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 the expression cannot be evaluated.
       * @throws NullPointerException If  <code>source</code> is <code>null</code>.
       */
      public String evaluate(InputSource source)
          throws XPathExpressionException {
          return (String)this.evaluate( source, XPathConstants.STRING );
      }
  
      private boolean isSupported( QName returnType ) {
          // XPathConstants.STRING
          if ( ( returnType.equals( XPathConstants.STRING ) ) ||
               ( returnType.equals( XPathConstants.NUMBER ) ) ||
               ( returnType.equals( XPathConstants.BOOLEAN ) ) ||
               ( returnType.equals( XPathConstants.NODE ) ) ||
               ( returnType.equals( XPathConstants.NODESET ) )  ) {
      
              return true;
          }
          return false;
       }
  
       private Object getResultAsType( XObject resultObject, QName returnType )
          throws javax.xml.transform.TransformerException {
          // XPathConstants.STRING
          if ( returnType.equals( XPathConstants.STRING ) ) {
              return resultObject.str();
          }
          // XPathConstants.NUMBER
          if ( returnType.equals( XPathConstants.NUMBER ) ) {
              return new Double ( resultObject.num());
          }
          // XPathConstants.BOOLEAN
          if ( returnType.equals( XPathConstants.BOOLEAN ) ) {
              return resultObject.bool() ? Boolean.TRUE : Boolean.FALSE;
          }
          // XPathConstants.NODESET ---ORdered, UNOrdered???
          if ( returnType.equals( XPathConstants.NODESET ) ) {
              return resultObject.nodelist();
          }
          // XPathConstants.NODE
          if ( returnType.equals( XPathConstants.NODE ) ) {
              NodeIterator ni = resultObject.nodeset();
              //Return the first node, or null
              return ni.nextNode();
          }
          // If isSupported check is already done then the execution path 
          // shouldn't come here. Being defensive
          String fmsg = XSLMessages.createXPATHMessage( 
                  XPATHErrorResources.ER_UNSUPPORTED_RETURN_TYPE,
                  new Object[] { returnType.toString()});
          throw new IllegalArgumentException ( fmsg );
      }
  
  
      private static Document getDummyDocument( ) {
          try {
              if ( dbf == null ) {
                  dbf = DocumentBuilderFactory.newInstance();
                  dbf.setNamespaceAware( true );
                  dbf.setValidating( false );
              }
              db = dbf.newDocumentBuilder();
  
              DOMImplementation dim = db.getDOMImplementation();
              d = dim.createDocument("http://java.sun.com/jaxp/xpath",
                  "dummyroot", null);
              return d;
          } catch ( Exception e ) {
              e.printStackTrace();
          }
          return null;
      }
  
  
  
  
  }
  