reflectivevisitor.java

drools 一个开放源码的规则引擎

package org.drools.reteoo;

/*
 * $Id: ReflectiveVisitor.java,v 1.7 2005/04/20 00:03:06 mproctor Exp $
 *
 * Copyright 2004-2004 (C) The Werken Company. All Rights Reserved.
 *
 * 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 "drools" must not be used to endorse or promote products derived
 * from this Software without prior written permission of The Werken Company.
 * For written permission, please contact [e-mail].
 *
 * 4. Products derived from this Software may not be called "drools" nor may
 * "drools" appear in their names without prior written permission of The Werken
 * Company. "drools" is a trademark of The Werken Company.
 *
 * 5. Due credit should be given to The Werken Company. (http://werken.com/)
 *
 * THIS SOFTWARE IS PROVIDED BY THE WERKEN COMPANY 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 THE WERKEN COMPANY 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.
 *
 */

import java.lang.reflect.Method;

import org.drools.Visitor;

/**
 * Java Tip 98: Reflect on the Visitor design pattern. Implement visitors in
 * Java, using reflection.
 * http://www.javaworld.com/javaworld/javatips/jw-javatip98.html
 *
 * @author Jeremy Blosser
 */
public abstract class ReflectiveVisitor
    implements
    Visitor
{
    static final String newline = System.getProperty( "line.separator" );

    public void visit(Object object)
    {
        try
        {
            if ( object != null )
            {
                Method method = getMethod( object.getClass( ) );
                method.invoke( this,
                               new Object[]{object} );
            }
            else
            {
                Method method = getClass( ).getMethod( "visitNull",
                                                       ( Class[] ) null );
                method.invoke( this,
                               ( Object[] ) null );
            }
        }
        catch ( Exception e )
        {
            e.printStackTrace( );
        }
    }

    private Method getMethod(Class clazz)
    {
        Class newClazz = clazz;
        Method method = null;

        // Try the superclasses
        while ( method == null && newClazz != Object.class )
        {
            String methodName = newClazz.getName( );
            methodName = "visit" + methodName.substring( methodName.lastIndexOf( '.' ) + 1 );
            try
            {
                method = getClass( ).getMethod( methodName,
                                                new Class[]{newClazz} );
            }
            catch ( NoSuchMethodException e )
            {
                newClazz = newClazz.getSuperclass( );
            }
        }

        // Try the interfaces.
        if ( newClazz == Object.class )
        {
            Class[] interfaces = clazz.getInterfaces( );
            for ( int i = 0; i < interfaces.length; i++ )
            {
                String methodName = interfaces[i].getName( );
                methodName = "visit" + methodName.substring( methodName.lastIndexOf( '.' ) + 1 );
                try
                {
                    method = getClass( ).getMethod( methodName,
                                                    new Class[]{interfaces[i]} );
                }
                catch ( NoSuchMethodException e )
                {
                    // swallow
                }
            }
        }
        if ( method == null )
        {
            try
            {
                method = getClass( ).getMethod( "visitObject",
                                                new Class[]{Object.class} );
            }
            catch ( Exception e )
            {
                // Shouldn't happen as long as all Visitors extend this class
                // and this class continues to implement visitObject(Object).
                e.printStackTrace( );
            }
        }
        return method;
    }

    public void visitObject(Object object)
    {
        System.err.println( "no visitor implementation for : " + object.getClass( ) + " : " + object );
    }
}