xpathimpl.java

java1.6众多例子参考

        }

        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 new Boolean( resultObject.bool());
        }
        // 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 {
            com.sun.org.apache.xpath.internal.XPath xpath = new XPath (expression, null,
                    prefixResolver, com.sun.org.apache.xpath.internal.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;
    }
 
}