// NewInstance.java - create a new instance of a class by name.
// http://www.saxproject.org
// Written by Edwin Goei, edwingo@apache.org
// and by David Brownell, dbrownell@users.sourceforge.net
// NO WARRANTY!  This class is in the Public Domain.
// $Id: NewInstance.java 670295 2008-06-22 01:46:43Z mrglavas $

package org.xml.sax.helpers;

Create a new instance of a class by name.

This module, both source code and documentation, is in the
Public Domain, and comes with NO WARRANTY.
See http://www.saxproject.org
for further information.

This class contains a static method for creating an instance of a
class from an explicit class name.  It tries to use the thread's context
ClassLoader if possible and falls back to using
Class.forName(String).  It also takes into account JDK 1.2+'s
AccessController mechanism for performing its actions.  
This code is designed to compile and run on JDK version 1.1 and later
including versions of Java 2.
This is not the NewInstance accompanying SAX 2.0.2; it
represents many fixes to that code.
Author:
Edwin Goei, David Brownell
Version:
2.0.1 (sax2r2)/**
 * Create a new instance of a class by name.
 *
 * <blockquote>
 * <em>This module, both source code and documentation, is in the
 * Public Domain, and comes with <strong>NO WARRANTY</strong>.</em>
 * See <a href='http://www.saxproject.org'>http://www.saxproject.org</a>
 * for further information.
 * </blockquote>
 *
 * <p>This class contains a static method for creating an instance of a
 * class from an explicit class name.  It tries to use the thread's context
 * ClassLoader if possible and falls back to using
 * Class.forName(String).  It also takes into account JDK 1.2+'s
 * AccessController mechanism for performing its actions.  </p>
 *
 * <p>This code is designed to compile and run on JDK version 1.1 and later
 * including versions of Java 2.</p>
 *
 * <p>This is <strong>not</strong> the NewInstance accompanying SAX 2.0.2; it
 * represents many fixes to that code.
 * 
 * @author Edwin Goei, David Brownell
 * @version 2.0.1 (sax2r2)
 */
class NewInstance {
    
    // constants

    // governs whether, if we fail in finding a class even
    // when given a classloader, we'll make a last-ditch attempt
    // to use the current classloader.  
    private static final boolean DO_FALLBACK = true;

    
Creates a new instance of the specified class name
Package private so this code is not exposed at the API level.
/**
     * Creates a new instance of the specified class name
     *
     * Package private so this code is not exposed at the API level.
     */
    static Object newInstance (ClassLoader classLoader, String className)
        throws ClassNotFoundException, IllegalAccessException,
            InstantiationException
    {
        Class driverClass;
        if (classLoader == null) {
            // XXX Use the bootstrap ClassLoader.  There is no way to
            // load a class using the bootstrap ClassLoader that works
            // in both JDK 1.1 and Java 2.  However, this should still
            // work b/c the following should be true:
            //
            // (cl == null) iff current ClassLoader == null
            //
            // Thus Class.forName(String) will use the current
            // ClassLoader which will be the bootstrap ClassLoader.
            driverClass = Class.forName(className);
        } else {
            try {
                driverClass = classLoader.loadClass(className);
            } catch (ClassNotFoundException x) {
                if (DO_FALLBACK) {
                    // Fall back to current classloader
                    classLoader = NewInstance.class.getClassLoader();
                    if (classLoader != null) {
                        driverClass = classLoader.loadClass(className);
                    }
                    else {
                        driverClass = Class.forName(className);
                    }
                } else {
                    throw x;
                }
            }
        }
        Object instance = driverClass.newInstance();
        return instance;
    }

    
Figure out which ClassLoader to use.  For JDK 1.2 and later use
the context ClassLoader.
/**
     * Figure out which ClassLoader to use.  For JDK 1.2 and later use
     * the context ClassLoader.
     */           
    static ClassLoader getClassLoader ()
    {
        // Figure out which ClassLoader to use for loading the provider
        // class.  If there is a Context ClassLoader then use it.
        ClassLoader cl = SecuritySupport.getContextClassLoader();
        if (cl == null) {
            // Assert: we are on JDK 1.1 or we have no Context ClassLoader
            // so use the current ClassLoader
            cl = NewInstance.class.getClassLoader();
        }
        return cl;
    }
}