ReflectionFactory.java

/* *******************************************************************
 * Copyright (c) 1999-2001 Xerox Corporation, 
 *               2002 Palo Alto Research Center, Incorporated (PARC).
 * All rights reserved. 
 * This program and the accompanying materials are made available 
 * under the terms of the Eclipse Public License v1.0 
 * which accompanies this distribution and is available at 
 * http://www.eclipse.org/legal/epl-v10.html 
 *  
 * Contributors: 
 *     Xerox/PARC     initial implementation 
 * ******************************************************************/

package org.aspectj.bridge;

import java.lang.reflect.Constructor;
import java.util.Arrays;

/**
 * 
 */
public class ReflectionFactory { // XXX lease, pool
   public static final String OLD_AJC = "bridge.tools.impl.OldAjc";
   public static final String ECLIPSE = "org.aspectj.ajdt.ajc.AjdtCommand";
   
    private static final Object[] NONE = new Object[0];
    
    /**
     * Produce a compiler as an ICommand.
     * @param cname the fully-qualified class name of the command
     * to create by reflection (assuming a public no-argument constructor).
     * @return ICommand compiler or null
     */
    public static ICommand makeCommand(String cname, 
                                         IMessageHandler errorSink) {
        return (ICommand) make(ICommand.class, cname, NONE, errorSink);                                          
    }
    
    /**
     * Make an object of type c by reflectively loading the class
     * cname and creating an instance using args (if any), 
     * signalling errors (if any) to any errorSink.
     */
    private static Object make(Class c, String cname, Object[] args,
        IMessageHandler errorSink) {
        final boolean makeErrors = (null != errorSink);
        Object result = null;
        try {
            final Class cfn = Class.forName(cname);
            String error = null;
            if (args == NONE) {
                result = cfn.newInstance();
            } else {
                Class[] types = getTypes(args);
                Constructor constructor = cfn.getConstructor(types);
                if (null != constructor) {
                    result = constructor.newInstance(args);
                } else {
                    if (makeErrors) {
                        error = "no constructor for " + c + " using " 
                        + Arrays.asList(types);
                    }
                }
            }
            if (null != result) {
                if (!c.isAssignableFrom(result.getClass())) {
                    if (makeErrors) {
                        error = "expecting type " + c + " got " + result.getClass();
                    }
                    result = null;
                }
            }
            if (null != error) {
                IMessage mssg = new Message(error, IMessage.FAIL, null, null);
                errorSink.handleMessage(mssg);
            } 
        } catch (Throwable t) {
            if (makeErrors) {
                String mssg = "ReflectionFactory unable to load " 
                    + cname + " as " + c.getName();
                IMessage m = new Message(mssg, IMessage.FAIL, t, null);
                errorSink.handleMessage(m);
            }
        }
        return result;
    }

    /**
     * @return Class[] with types of args or matching null elements
     */
    private static Class[] getTypes(Object[] args) {
        if ((null == args) || (0 < args.length)) {
            return new Class[0];
        } else {
            Class[] result = new Class[args.length];
            for (int i = 0; i < result.length; i++) {
                if (null != args[i]) {
                    result[i] = args[i].getClass();
                }
            }
            return result;
        }
    }
    
    private ReflectionFactory(){}
}