001/*
002 * Copyright 2002-2018 the original author or authors.
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 *      https://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017package org.springframework.web.context;
018
019import javax.servlet.ServletContext;
020import javax.servlet.ServletException;
021
022import org.apache.commons.logging.Log;
023import org.apache.commons.logging.LogFactory;
024
025import org.springframework.context.ApplicationContextInitializer;
026import org.springframework.lang.Nullable;
027import org.springframework.web.WebApplicationInitializer;
028
029/**
030 * Convenient base class for {@link WebApplicationInitializer} implementations
031 * that register a {@link ContextLoaderListener} in the servlet context.
032 *
033 * <p>The only method required to be implemented by subclasses is
034 * {@link #createRootApplicationContext()}, which gets invoked from
035 * {@link #registerContextLoaderListener(ServletContext)}.
036 *
037 * @author Arjen Poutsma
038 * @author Chris Beams
039 * @author Juergen Hoeller
040 * @since 3.2
041 */
042public abstract class AbstractContextLoaderInitializer implements WebApplicationInitializer {
043
044        /** Logger available to subclasses. */
045        protected final Log logger = LogFactory.getLog(getClass());
046
047
048        @Override
049        public void onStartup(ServletContext servletContext) throws ServletException {
050                registerContextLoaderListener(servletContext);
051        }
052
053        /**
054         * Register a {@link ContextLoaderListener} against the given servlet context. The
055         * {@code ContextLoaderListener} is initialized with the application context returned
056         * from the {@link #createRootApplicationContext()} template method.
057         * @param servletContext the servlet context to register the listener against
058         */
059        protected void registerContextLoaderListener(ServletContext servletContext) {
060                WebApplicationContext rootAppContext = createRootApplicationContext();
061                if (rootAppContext != null) {
062                        ContextLoaderListener listener = new ContextLoaderListener(rootAppContext);
063                        listener.setContextInitializers(getRootApplicationContextInitializers());
064                        servletContext.addListener(listener);
065                }
066                else {
067                        logger.debug("No ContextLoaderListener registered, as " +
068                                        "createRootApplicationContext() did not return an application context");
069                }
070        }
071
072        /**
073         * Create the "<strong>root</strong>" application context to be provided to the
074         * {@code ContextLoaderListener}.
075         * <p>The returned context is delegated to
076         * {@link ContextLoaderListener#ContextLoaderListener(WebApplicationContext)} and will
077         * be established as the parent context for any {@code DispatcherServlet} application
078         * contexts. As such, it typically contains middle-tier services, data sources, etc.
079         * @return the root application context, or {@code null} if a root context is not
080         * desired
081         * @see org.springframework.web.servlet.support.AbstractDispatcherServletInitializer
082         */
083        @Nullable
084        protected abstract WebApplicationContext createRootApplicationContext();
085
086        /**
087         * Specify application context initializers to be applied to the root application
088         * context that the {@code ContextLoaderListener} is being created with.
089         * @since 4.2
090         * @see #createRootApplicationContext()
091         * @see ContextLoaderListener#setContextInitializers
092         */
093        @Nullable
094        protected ApplicationContextInitializer<?>[] getRootApplicationContextInitializers() {
095                return null;
096        }
097
098}