contextloader.java

spring framework 2.5.4源代码

/*
 * Copyright 2002-2008 the original author or authors.
 *
 * 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.springframework.web.context;

import java.io.IOException;
import java.util.Map;
import java.util.Properties;

import javax.servlet.ServletContext;

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

import org.springframework.beans.BeanUtils;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.access.BeanFactoryLocator;
import org.springframework.beans.factory.access.BeanFactoryReference;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextException;
import org.springframework.context.access.ContextSingletonBeanFactoryLocator;
import org.springframework.core.CollectionFactory;
import org.springframework.core.io.ClassPathResource;
import org.springframework.core.io.support.PropertiesLoaderUtils;
import org.springframework.util.ClassUtils;

/**
 * Performs the actual initialization work for the root application context.
 * Called by {@link ContextLoaderListener} and {@link ContextLoaderServlet}.
 *
 * <p>Looks for a {@link #CONTEXT_CLASS_PARAM "contextClass"} parameter
 * at the <code>web.xml</code> context-param level to specify the context
 * class type, falling back to the default of
 * {@link org.springframework.web.context.support.XmlWebApplicationContext}
 * if not found. With the default ContextLoader implementation, any context class
 * specified needs to implement the ConfigurableWebApplicationContext interface.
 *
 * <p>Processes a {@link #CONFIG_LOCATION_PARAM "contextConfigLocation"}
 * context-param and passes its value to the context instance, parsing it into
 * potentially multiple file paths which can be separated by any number of
 * commas and spaces, e.g. "WEB-INF/applicationContext1.xml,
 * WEB-INF/applicationContext2.xml". Ant-style path patterns are supported as well,
 * e.g. "WEB-INF/*Context.xml,WEB-INF/spring*.xml" or "WEB-INF/&#42;&#42;/*Context.xml".
 * If not explicitly specified, the context implementation is supposed to use a
 * default location (with XmlWebApplicationContext: "/WEB-INF/applicationContext.xml").
 *
 * <p>Note: In case of multiple config locations, later bean definitions will
 * override ones defined in previously loaded files, at least when using one of
 * Spring's default ApplicationContext implementations. This can be leveraged
 * to deliberately override certain bean definitions via an extra XML file.
 *
 * <p>Above and beyond loading the root application context, this class
 * can optionally load or obtain and hook up a shared parent context to
 * the root application context. See the
 * {@link #loadParentContext(ServletContext)} method for more information.
 *
 * @author Juergen Hoeller
 * @author Colin Sampaleanu
 * @author Sam Brannen
 * @since 17.02.2003
 * @see ContextLoaderListener
 * @see ContextLoaderServlet
 * @see ConfigurableWebApplicationContext
 * @see org.springframework.web.context.support.XmlWebApplicationContext
 */
public class ContextLoader {

	/**
	 * Config param for the root WebApplicationContext implementation class to
	 * use: "<code>contextClass</code>"
	 */
	public static final String CONTEXT_CLASS_PARAM = "contextClass";

	/**
	 * Name of servlet context parameter (i.e., "<code>contextConfigLocation</code>")
	 * that can specify the config location for the root context, falling back
	 * to the implementation's default otherwise.
	 * @see org.springframework.web.context.support.XmlWebApplicationContext#DEFAULT_CONFIG_LOCATION
	 */
	public static final String CONFIG_LOCATION_PARAM = "contextConfigLocation";

	/**
	 * Optional servlet context parameter (i.e., "<code>locatorFactorySelector</code>")
	 * used only when obtaining a parent context using the default implementation
	 * of {@link #loadParentContext(ServletContext servletContext)}.
	 * Specifies the 'selector' used in the
	 * {@link ContextSingletonBeanFactoryLocator#getInstance(String selector)}
	 * method call, which is used to obtain the BeanFactoryLocator instance from
	 * which the parent context is obtained.
	 * <p>The default is <code>classpath*:beanRefContext.xml</code>,
	 * matching the default applied for the
	 * {@link ContextSingletonBeanFactoryLocator#getInstance()} method.
	 * Supplying the "parentContextKey" parameter is sufficient in this case.
	 */
	public static final String LOCATOR_FACTORY_SELECTOR_PARAM = "locatorFactorySelector";

	/**
	 * Optional servlet context parameter (i.e., "<code>parentContextKey</code>")
	 * used only when obtaining a parent context using the default implementation
	 * of {@link #loadParentContext(ServletContext servletContext)}.
	 * Specifies the 'factoryKey' used in the
	 * {@link BeanFactoryLocator#useBeanFactory(String factoryKey)} method call,
	 * obtaining the parent application context from the BeanFactoryLocator instance.
	 * <p>Supplying this "parentContextKey" parameter is sufficient when relying
	 * on the default <code>classpath*:beanRefContext.xml</code> selector for
	 * candidate factory references.
	 */
	public static final String LOCATOR_FACTORY_KEY_PARAM = "parentContextKey";

	/**
	 * Name of the class path resource (relative to the ContextLoader class)
	 * that defines ContextLoader's default strategy names.
	 */
	private static final String DEFAULT_STRATEGIES_PATH = "ContextLoader.properties";


	private static final Properties defaultStrategies;

	static {
		// Load default strategy implementations from properties file.
		// This is currently strictly internal and not meant to be customized
		// by application developers.
		try {
			ClassPathResource resource = new ClassPathResource(DEFAULT_STRATEGIES_PATH, ContextLoader.class);
			defaultStrategies = PropertiesLoaderUtils.loadProperties(resource);
		}
		catch (IOException ex) {
			throw new IllegalStateException("Could not load 'ContextLoader.properties': " + ex.getMessage());
		}
	}


	private static final Log logger = LogFactory.getLog(ContextLoader.class);

	/**
	 * Map from (thread context) ClassLoader to WebApplicationContext.
	 * Often just holding one reference - if the ContextLoader class is
	 * deployed in the web app ClassLoader itself!
	 */
	private static final Map currentContextPerThread = CollectionFactory.createConcurrentMapIfPossible(1);

	/**
	 * The root WebApplicationContext instance that this loader manages.
	 */
	private WebApplicationContext context;

	/**
	 * Holds BeanFactoryReference when loading parent factory via
	 * ContextSingletonBeanFactoryLocator.
	 */
	private BeanFactoryReference parentContextRef;


	/**
	 * Initialize Spring's web application context for the given servlet context,
	 * according to the "{@link #CONTEXT_CLASS_PARAM contextClass}" and
	 * "{@link #CONFIG_LOCATION_PARAM contextConfigLocation}" context-params.
	 * @param servletContext current servlet context
	 * @return the new WebApplicationContext
	 * @throws IllegalStateException if there is already a root application context present
	 * @throws BeansException if the context failed to initialize
	 * @see #CONTEXT_CLASS_PARAM
	 * @see #CONFIG_LOCATION_PARAM
	 */
	public WebApplicationContext initWebApplicationContext(ServletContext servletContext)
			throws IllegalStateException, BeansException {

		if (servletContext.getAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE) != null) {
			throw new IllegalStateException(
					"Cannot initialize context because there is already a root application context present - " +
					"check whether you have multiple ContextLoader* definitions in your web.xml!");
		}

		servletContext.log("Initializing Spring root WebApplicationContext");
		if (logger.isInfoEnabled()) {
			logger.info("Root WebApplicationContext: initialization started");
		}
		long startTime = System.currentTimeMillis();

		try {
			// Determine parent for root web application context, if any.