WOInject.java

/**
 * Copyright (C) 2010 hprange <hprange@gmail.com>
 * 
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not
 * use this file except in compliance with the License. You may obtain a copy of
 * the License at
 * 
 * http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations under
 * the License.
 */
package com.woinject;

import java.security.AccessController;
import java.security.PrivilegedAction;

import javassist.ClassPool;
import javassist.CtClass;
import javassist.CtMethod;
import javassist.Loader;

/**
 * The <code>WOInject</code> class initializes the application intercepting core
 * methods used by WebObjects classes to create objects.
 * <p>
 * How to use:
 * 
 * <pre>
 * public static void main(String[] argv) {
 *     WOInject.init("com.company.app.Application", argv);
 * }
 * </pre>
 * <p>
 * <strong>Note</strong>: to ensure well functioning, do not obtain the
 * <code>Application</code> class name programmatically. No WebObjects classes
 * should be loaded before the WOInject initialization.
 * 
 * @author <a href="mailto:hprange@gmail.com">Henrique Prange</a>
 * @since 1.0
 */
public class WOInject {
    /**
     * Initialize the <code>WOApplication</code> with the WOInject capabilities.
     * 
     * @param applicationClass
     *            the name of the application class
     * @param args
     *            the application's command line arguments
     */
    public static void init(String applicationClass, String[] args) {
        final ClassPool pool = ClassPool.getDefault();

        Loader loader = AccessController.doPrivileged(new PrivilegedAction<Loader>() {
            public Loader run() {
                return new Loader(pool);
            }
        });

        loader.delegateLoadingOf("com.apple.");

        try {
            CtClass clazz = pool.get("com.webobjects.foundation._NSUtilities");
            CtMethod method = clazz.getDeclaredMethod("instantiateObject");

            method.insertBefore("{ return com.webobjects.foundation.InstantiationInterceptor.instantiateObject($1, $2, $3, $4, $5); }");

            method = clazz.getDeclaredMethod("instantiateObjectWithConstructor");

            method.insertBefore("{ return com.webobjects.foundation.InstantiationInterceptor.instantiateObject($1, $2, $3, $4, $5); }");

            Thread.currentThread().setContextClassLoader(loader);

            Class<?> erxApp = loader.loadClass("er.extensions.appserver.ERXApplication");

            Class<?> app = loader.loadClass(applicationClass);

            Class<?> injectableApp = loader.loadClass("com.woinject.InjectableApplication");

            if (!injectableApp.isAssignableFrom(app)) {
                throw new Error("Cannot initialize the injector. The Application class doesn't extend InjectableApplication.");
            }

            erxApp.getDeclaredMethod("main", String[].class, Class.class).invoke(null, args, app);
        } catch (Throwable exception) {
            throw new Error("Cannot initialize the application to take advantage of WOInject features.", exception);
        }
    }
}