org.directwebremoting.HubFactory Maven / Gradle / Ivy

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DWR is easy Ajax for Java. It makes it simple to call Java code directly from Javascript. It gets rid of almost all the boiler plate code between the web browser and your Java code.

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/*
 * Copyright 2005 Joe Walker
 *
 * 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.directwebremoting;

import javax.servlet.ServletContext;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

/**
 * An accessor for the current Hub
 * @author Joe Walker [joe at getahead dot ltd dot uk]
 */
public class HubFactory
{
    /**
     * Accessor for the current Hub.
     * @return The current Hub.
     */
    public static Hub get()
    {
        if (builder == null)
        {
            log.warn("HubBuilder is null. This probably means that DWR has not initialized properly");
            return null;
        }

        return builder.get();
    }

    /**
     * Accessor for the current Hub in more complex setups.
     * For some setups DWR may not be able to discover the correct environment
     * (i.e. ServletContext), so we need to tell it. This generally happens if
     * you have DWR configured twice in a single context. Unless you are writing
     * code that someone else will configure, it is probably safe to use the
     * simpler {@link #get()} method.
     * @param ctx The servlet context to allow us to bootstrap
     * @return The current Hub.
     */
    public static Hub get(ServletContext ctx)
    {
        if (builder == null)
        {
            log.warn("HubBuilder is null. This probably means that DWR has not initialized properly");
            return null;
        }

        return builder.get(ctx);
    }

    /**
     * Internal method to allow us to get the HubBuilder from which we
     * will get Hub objects.
     * Do not call this method from outside of DWR.
     * @param builder The factory object (from DwrServlet)
     */
    public static void setHubBuilder(HubBuilder builder)
    {
        HubFactory.builder = builder;
    }

    /**
     * The HubBuilder from which we will get Hub objects
     */
    private static HubBuilder builder = null;

    /**
     * Class to enable us to access servlet parameters.
     */
    public interface HubBuilder
    {
        /**
         * Make the current webapp know what the current config/context is.
         * This method is only for use internally to DWR.
         * @param context The servlet context
         */
        void set(ServletContext context);

        /**
         * Accessor for the current Hub.
         * For some setups DWR may not be able to discover the correct
         * environment (i.e. ServletContext), so we need to tell it.
         * @param context The web application environment
         * @return The Hub that is associated with this web application
         */
        Hub get(ServletContext context);

        /**
         * Accessor for the current Hub
         * @return The Hub that is associated with this web application
         */
        Hub get();
    }

    /**
     * The log stream
     */
    private static final Log log = LogFactory.getLog(WebContextFactory.class);
}