org.apache.felix.eventadmin/src/main/java/org/apache/felix/eventadmin/impl/security/SecureEventAdminFactory.java

/*
 *   Copyright 2005 The Apache Software Foundation
 *
 *   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 org.apache.felix.eventadmin.impl.security;

import org.osgi.framework.Bundle;
import org.osgi.framework.ServiceFactory;
import org.osgi.framework.ServiceRegistration;
import org.osgi.service.event.EventAdmin;

/**
 * This class is a factory that secures a given <tt>EventAdmin</tt> service by
 * wrapping it with a new instance of an <tt>EventAdminSecurityDecorator</tt> on
 * any call to its <tt>getService()</tt> method. The decorator will determine the 
 * appropriate permissions by using the given permission factory and the bundle 
 * parameter passed to the <tt>getService()</tt> method. 
 * 
 * @author <a href="mailto:felix-dev@incubator.apache.org">Felix Project Team</a>
 */
public class SecureEventAdminFactory implements ServiceFactory
{
    // The EventAdmin to secure
    private EventAdmin m_admin;
    
    // The permission factory
    private final TopicPermissions m_topicPermissions;
    
    /**
     * The constructor of the factory. The factory will use the given event admin and
     * permission factory to create a new <tt>EventAdminSecurityDecorator</tt>
     * on any call to <tt>getService()</tt>. 
     * 
     * @param admin The <tt>EventAdmin</tt> service to secure.
     * @param topicPermissions The permission factory to use for permission lookup.
     */
    public SecureEventAdminFactory(final EventAdmin admin, final TopicPermissions 
        topicPermissions)
    {
        checkNull(admin, "Admin");
        checkNull(topicPermissions, "TopicPermissions");
        
        m_admin = admin;
        
        m_topicPermissions = topicPermissions;
    }

    /**
     * Returns a new <tt>EventAdminSecurityDecorator</tt> initialized with the
     * given <tt>EventAdmin</tt>. That in turn will check any call to post or
     * send for the appropriate permissions based on the bundle parameter.
     * 
     * @param bundle The bundle used to determine the permissions of the caller
     * @param registration The ServiceRegistration that is not used
     * 
     * @return The given service instance wrapped by an <tt>EventAdminSecuriryDecorator</tt> 
     * 
     * @see org.osgi.framework.ServiceFactory#getService(org.osgi.framework.Bundle,
     *      org.osgi.framework.ServiceRegistration)
     */
    public Object getService(final Bundle bundle,
        final ServiceRegistration registration)
    {
        // We don't need to cache this objects since the framework already does this.
        return new EventAdminSecurityDecorator(bundle, m_admin, m_topicPermissions);
    }

    /**
     * This method doesn't do anything at the moment.
     * 
     * @param bundle The bundle object that is not used
     * @param registration The ServiceRegistration that is not used
     * @param service The service object that is not used
     * 
     * @see org.osgi.framework.ServiceFactory#ungetService(org.osgi.framework.Bundle,
     *      org.osgi.framework.ServiceRegistration, java.lang.Object)
     */
    public void ungetService(final Bundle bundle,
        final ServiceRegistration registration, final Object service)
    {
        // We don't need to do anything here since we hand-out a new instance with
        // any call to getService hence, it is o.k. to just wait for the next gc.
    }
    
    /*
     * This is a utility method that will throw a <tt>NullPointerException</tt>
     * in case that the given object is null. The message will be of the form name +
     * may not be null.
     */
    private void checkNull(final Object object, final String name)
    {
        if(null == object)
        {
            throw new NullPointerException(name + " may not be null");
        }
    }
}