saxhelper.java

Java的面向对象数据库系统的源代码

/*
 * Copyright 2001 (C) MetaStuff, Ltd. All Rights Reserved.
 * 
 * This software is open source. 
 * See the bottom of this file for the licence.
 * 
 * $Id: SAXHelper.java,v 1.12 2003/04/07 22:14:08 jstrachan Exp $
 */

package org.dom4j.io;

import org.xml.sax.SAXException;
import org.xml.sax.SAXNotRecognizedException;
import org.xml.sax.SAXNotSupportedException;
import org.xml.sax.XMLReader;
import org.xml.sax.helpers.XMLReaderFactory;

/** <p><code>SAXHelper</code> contains some helper methods for working with 
  * SAX and XMLReader objects.
  *
  * @author <a href="mailto:[e-mail]">James Strachan</a>
  * @version $Revision: 1.12 $
  */
class SAXHelper {

    private static boolean loggedWarning = true;
    
    public static boolean setParserProperty(XMLReader reader, String propertyName, Object value) {    
        try {
            reader.setProperty(propertyName, value);
            return true;
        } 
        catch (SAXNotSupportedException e) {
            // ignore
        } 
        catch (SAXNotRecognizedException e) {
            // ignore
        }
        return false;
    }

    public static boolean setParserFeature(XMLReader reader, String featureName, boolean value) {    
        try {
            reader.setFeature(featureName, value);
            return true;
        } 
        catch (SAXNotSupportedException e) {
            // ignore
        } 
        catch (SAXNotRecognizedException e) {
            // ignore
        }
        return false;
    }

    /** Creats a default XMLReader via the org.xml.sax.driver system property 
      * or JAXP if the system property is not set.
      */
    public static XMLReader createXMLReader(boolean validating) throws SAXException {
        XMLReader reader = null;
        if ( classNameAvailable( "javax.xml.parsers.SAXParserFactory" ) ) {
            // don't attempt to use JAXP if it is not in the ClassPath
            reader = createXMLReaderViaJAXP( validating, true );
        }
        if ( reader == null ) {
            if ( reader == null ) {
                // lets try just use JAXP, maybe its a classloader issue
                reader = createXMLReaderViaJAXP( validating, true );
            }
            if ( reader == null ) {
                try {
                    reader = XMLReaderFactory.createXMLReader();
                }
                catch (Exception e) {
                    if ( isVerboseErrorReporting() ) {
                        // log all exceptions as warnings and carry
                        // on as we have a default SAX parser we can use
                        System.out.println( 
                            "Warning: Caught exception attempting to use SAX to "
                             + "load a SAX XMLReader " 
                        );
                        System.out.println( "Warning: Exception was: " + e );
                        System.out.println( 
                            "Warning: I will print the stack trace then carry on "
                             + "using the default SAX parser" 
                         );
                        e.printStackTrace();
                    }
                    else {
                        System.out.println( 
                            "Warning: Error occurred using SAX to load a SAXParser. Will use Aelfred instead" 
                        );
                    }
                }
            }
            if ( reader == null ) {
                throw new SAXException( "Could not initialize a SAX Parser. Please add a SAX parser to your classpath along with preferably jaxp.jar" );
            }
        }
        return reader;
    }

    /** This method attempts to use JAXP to locate the  
      * SAX2 XMLReader implementation.  
      * This method uses reflection to avoid being dependent directly
      * on the JAXP classes.
      */
    protected static XMLReader createXMLReaderViaJAXP(boolean validating, boolean namespaceAware) {
        // try use JAXP to load the XMLReader...
        try {
            return JAXPHelper.createXMLReader( validating, namespaceAware );
        }
        catch (Throwable e) {
            if ( ! loggedWarning ) {                    
                loggedWarning = true;
                if ( isVerboseErrorReporting() ) {
                    // log all exceptions as warnings and carry
                    // on as we have a default SAX parser we can use
                    System.out.println( 
                        "Warning: Caught exception attempting to use JAXP to "
                         + "load a SAX XMLReader " 
                    );
                    System.out.println( "Warning: Exception was: " + e );
                    System.out.println( 
                        "Warning: I will print the stack trace then carry on "
                         + "using the default SAX parser" 
                     );
                    e.printStackTrace();
                }
                else {
                    System.out.println( 
                        "Warning: Error occurred using JAXP to load a SAXParser. Will use Aelfred instead" 
                    );
                }
            }
        }
        return null;
    }

    /** @return true if the given class could be found using the class loader which loaded this 
      * class
      */
    protected static boolean classNameAvailable( String className ) {
        try {            
            Class.forName( className, true, SAXHelper.class.getClassLoader() );
            return true;
        }
        catch (Exception e) {
            return false;
        }
    }
    
    protected static boolean isVerboseErrorReporting() {
        try {
            String flag = System.getProperty( "org.dom4j.verbose" );
            if ( flag != null && flag.equalsIgnoreCase( "true" ) ) {
                return true;
            }
        }
        catch (Exception e) {
            // in case a security exception
            // happens in an applet or similar JVM
        }
        return true;
    }
}




/*
 * Redistribution and use of this software and associated documentation
 * ("Software"), with or without modification, are permitted provided
 * that the following conditions are met:
 *
 * 1. Redistributions of source code must retain copyright
 *    statements and notices.  Redistributions must also contain a
 *    copy of this document.
 *
 * 2. Redistributions in binary form must reproduce the
 *    above copyright notice, this list of conditions and the
 *    following disclaimer in the documentation and/or other
 *    materials provided with the distribution.
 *
 * 3. The name "DOM4J" must not be used to endorse or promote
 *    products derived from this Software without prior written
 *    permission of MetaStuff, Ltd.  For written permission,
 *    please contact [e-mail].
 *
 * 4. Products derived from this Software may not be called "DOM4J"
 *    nor may "DOM4J" appear in their names without prior written
 *    permission of MetaStuff, Ltd. DOM4J is a registered
 *    trademark of MetaStuff, Ltd.
 *
 * 5. Due credit should be given to the DOM4J Project
 *    (http://dom4j.org/).
 *
 * THIS SOFTWARE IS PROVIDED BY METASTUFF, LTD. AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT
 * NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
 * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL
 * METASTUFF, LTD. OR ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
 * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
 * OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * Copyright 2001 (C) MetaStuff, Ltd. All Rights Reserved.
 *
 * $Id: SAXHelper.java,v 1.12 2003/04/07 22:14:08 jstrachan Exp $
 */