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.namespace.NamespaceContext;
  import javax.xml.xpath.XPathExpressionException;
  import javax.xml.xpath.XPathConstants;
  import javax.xml.xpath.XPathFunctionResolver;
  import javax.xml.xpath.XPathVariableResolver;
  import javax.xml.xpath.XPathExpression;
  
  import org.apache.xml.dtm.DTM;
  import org.apache.xpath.*;
  import org.apache.xpath.objects.XObject;
  import org.apache.xpath.res.XPATHErrorResources;
  import org.apache.xalan.res.XSLMessages;
  
  import org.w3c.dom.Node;
  import org.w3c.dom.DOMImplementation;
  import org.w3c.dom.Document;
  import org.w3c.dom.traversal.NodeIterator;
  
  import org.xml.sax.InputSource;
  import org.xml.sax.SAXException;
  
  import javax.xml.parsers.*;
  
  import java.io.IOException;
  
  /**
   * The XPathImpl class provides implementation for the methods defined  in
   * javax.xml.xpath.XPath interface. This provide simple access to the results
   * of an XPath expression.
   *
   *
   * @version $Revision$
   * @author  Ramesh Mandava
   */
  public class XPathImpl implements javax.xml.xpath.XPath {
  
      // Private variables
      private XPathVariableResolver variableResolver;
      private XPathFunctionResolver functionResolver;
      private XPathVariableResolver origVariableResolver;
      private XPathFunctionResolver origFunctionResolver;
      private NamespaceContext namespaceContext=null;
      private JAXPPrefixResolver prefixResolver;
      // 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; 
  
      XPathImpl( XPathVariableResolver vr, XPathFunctionResolver fr ) {
          this.origVariableResolver = this.variableResolver = vr;
          this.origFunctionResolver = this.functionResolver = fr;
      }
  
      XPathImpl( XPathVariableResolver vr, XPathFunctionResolver fr, 
              boolean featureSecureProcessing ) {
          this.origVariableResolver = this.variableResolver = vr;
          this.origFunctionResolver = this.functionResolver = fr;
          this.featureSecureProcessing = featureSecureProcessing;
      }
  
      /**
       * <p>Establishes a variable resolver.</p>
       *
       * @param resolver Variable Resolver
       */
      public void setXPathVariableResolver(XPathVariableResolver resolver) {
          if ( resolver == null ) {
              String fmsg = XSLMessages.createXPATHMessage( 
                      XPATHErrorResources.ER_ARG_CANNOT_BE_NULL,
                      new Object[] {"XPathVariableResolver"} );
              throw new NullPointerException( fmsg );
          }
          this.variableResolver = resolver;
      }
  
      /**
       * <p>Returns the current variable resolver.</p>
       *
       * @return Current variable resolver
       */
      public XPathVariableResolver getXPathVariableResolver() {
          return variableResolver;
      }
  
      /**
       * <p>Establishes a function resolver.</p>
       *
       * @param resolver XPath function resolver
       */
      public void setXPathFunctionResolver(XPathFunctionResolver resolver) {
          if ( resolver == null ) {
              String fmsg = XSLMessages.createXPATHMessage( 
                      XPATHErrorResources.ER_ARG_CANNOT_BE_NULL,
                      new Object[] {"XPathFunctionResolver"} );
              throw new NullPointerException( fmsg );
          }
          this.functionResolver = resolver;
      }
  
      /**
       * <p>Returns the current function resolver.</p>
       *
       * @return Current function resolver
       */
      public XPathFunctionResolver getXPathFunctionResolver() {
          return functionResolver;
      }
  
      /**
       * <p>Establishes a namespace context.</p>
       *
       * @param nsContext Namespace context to use
       */
      public void setNamespaceContext(NamespaceContext nsContext) {
          if ( nsContext == null ) {
              String fmsg = XSLMessages.createXPATHMessage( 
                      XPATHErrorResources.ER_ARG_CANNOT_BE_NULL,
                      new Object[] {"NamespaceContext"} );
              throw new NullPointerException( fmsg ); 
          }
          this.namespaceContext = nsContext;
          this.prefixResolver = new JAXPPrefixResolver ( nsContext );
      }
  
      /**
       * <p>Returns the current namespace context.</p>
       *
       * @return Current Namespace context
       */
      public NamespaceContext getNamespaceContext() {
          return namespaceContext;
      }
  
      private static Document d = null;
      
      private static DocumentBuilder getParser() {
          try {
              // we'd really like to cache those DocumentBuilders, but we can't because:
              // 1. thread safety. parsers are not thread-safe, so at least
              //    we need one instance per a thread.
              // 2. parsers are non-reentrant, so now we are looking at having a
              // pool of parsers.
              // 3. then the class loading issue. The look-up procedure of
              //    DocumentBuilderFactory.newInstance() depends on context class loader
              //    and system properties, which may change during the execution of JVM.
              //
              // so we really have to create a fresh DocumentBuilder every time we need one
              // - KK
              DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
              dbf.setNamespaceAware( true );
              dbf.setValidating( false );
              return dbf.newDocumentBuilder();
          } catch (ParserConfigurationException e) {
              // this should never happen with a well-behaving JAXP implementation. 
              throw new Error(e.toString());
          }
      }
  
      private static Document getDummyDocument( ) {
          // we don't need synchronization here; even if two threads
          // enter this code at the same time, we just waste a little time
          if(d==null) {
              DOMImplementation dim = getParser().getDOMImplementation();
              d = dim.createDocument("http://java.sun.com/jaxp/xpath",
                  "dummyroot", null);
          }
          return d;
      }
  
      
      private XObject eval(String expression, Object contextItem)
          throws javax.xml.transform.TransformerException {
          org.apache.xpath.XPath xpath = new org.apache.xpath.XPath( expression,
              null, prefixResolver, org.apache.xpath.XPath.SELECT ); 
          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);
          }
  
          XObject xobj = null;
          
          xpathSupport.setVarStack(new JAXPVariableStack(variableResolver));
          
          // If item is null, then we will create a a Dummy contextNode
          if ( contextItem instanceof Node ) {
              xobj = xpath.execute (xpathSupport, (Node)contextItem,
                      prefixResolver );
          } else {
              xobj = xpath.execute ( xpathSupport, DTM.NULL, prefixResolver );
          }
   
          return xobj;
      }
          
      /**
       * <p>Evaluate an <code>XPath</code> 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 <code>QName</code> resolution and return type conversion.</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>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 (node or node list, 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>.
       */
      public Object evaluate(String expression, Object item, QName returnType)
              throws XPathExpressionException {
          if ( expression == null ) {
              String fmsg = XSLMessages.createXPATHMessage( 
                      XPATHErrorResources.ER_ARG_CANNOT_BE_NULL,
                      new Object[] {"XPath expression"} );
              throw new NullPointerException ( fmsg );
          }
          if ( returnType == null ) {
              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 {
   
              XObject resultObject = eval( expression, item );
              return getResultAsType( resultObject, 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 );
              }
          } 
          
      }
  
      private boolean isSupported( QName returnType ) {
          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();
          }
          String fmsg = XSLMessages.createXPATHMessage(
                  XPATHErrorResources.ER_UNSUPPORTED_RETURN_TYPE,
                  new Object[] { returnType.toString()});
          throw new IllegalArgumentException( fmsg );
      }
           
              
          
      /**
       * <p>Evaluate an XPath expression in the specified context and return the result as a <code>String</code>.</p>
       *
       * <p>This method calls {@link #evaluate(String expression, Object item, QName returnType)} with a <code>returnType</code> of
       * {@link XPathConstants#STRING}.</p>
       *
       * <p>See "Evaluation of XPath Expressions" 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.
       * 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 (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 <code>expression</code> cannot be evaluated.
       * @throws NullPointerException If <code>expression</code> is <code>null</code>.
       */
      public String evaluate(String expression, Object item)
          throws XPathExpressionException {
          return (String)this.evaluate( expression, item, XPathConstants.STRING );
      }
  
      /**
       * <p>Compile an XPath expression for later evaluation.</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>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>.
       */
      public XPathExpression compile(String expression)
          throws XPathExpressionException {
          if ( expression == null ) {
              String fmsg = XSLMessages.createXPATHMessage( 
                      XPATHErrorResources.ER_ARG_CANNOT_BE_NULL,
                      new Object[] {"XPath expression"} );
              throw new NullPointerException ( fmsg );
          }
          try {
              org.apache.xpath.XPath xpath = new XPath (expression, null,
                      prefixResolver, org.apache.xpath.XPath.SELECT );
              // Can have errorListener
              XPathExpressionImpl ximpl = new XPathExpressionImpl (xpath,
                      prefixResolver, functionResolver, variableResolver,
                      featureSecureProcessing );
              return ximpl;
          } catch ( javax.xml.transform.TransformerException te ) {
              throw new XPathExpressionException ( te ) ;
          }
      }
  
  
      /**
       * <p>Evaluate an 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(String expression, 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>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>.
       */
      public Object evaluate(String expression, InputSource source, 
              QName returnType) throws XPathExpressionException {
          // Checking validity of different parameters
          if( source== null ) {
              String fmsg = XSLMessages.createXPATHMessage( 
                      XPATHErrorResources.ER_ARG_CANNOT_BE_NULL,
                      new Object[] {"source"} );
              throw new NullPointerException ( fmsg );
          }
          if ( expression == null ) {
              String fmsg = XSLMessages.createXPATHMessage( 
                      XPATHErrorResources.ER_ARG_CANNOT_BE_NULL,
                      new Object[] {"XPath expression"} );
              throw new NullPointerException ( fmsg );
          }
          if ( returnType == null ) {
              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 {
  
              Document document = getParser().parse( source );
  
              XObject resultObject = eval( expression, document );
              return getResultAsType( resultObject, returnType );
          } catch ( SAXException e ) {
              throw new XPathExpressionException ( e );
          } catch( IOException e ) {
              throw new XPathExpressionException ( e );            
          } catch ( javax.xml.transform.TransformerException te ) {
              Throwable nestedException = te.getException();
              if ( nestedException instanceof javax.xml.xpath.XPathFunctionException ) {
                  throw (javax.xml.xpath.XPathFunctionException)nestedException;
              } else {
                  throw new XPathExpressionException ( te );
              }
          }
  
      } 
   
  
  
  
      /**
       * <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>This method calls {@link #evaluate(String expression, 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>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>.
       */
      public String evaluate(String expression, InputSource source)
          throws XPathExpressionException {
          return (String)this.evaluate( expression, source, XPathConstants.STRING );
      }
  
      /**
       * <p>Reset this <code>XPath</code> to its original configuration.</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>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>
       */
      public void reset() {
          this.variableResolver = this.origVariableResolver;
          this.functionResolver = this.origFunctionResolver;
          this.namespaceContext = null;
      }
   
  }
  