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Spring Framework example source code file (ContextLoader.java)

This example Spring Framework source code file (ContextLoader.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Spring Framework tags/keywords

applicationcontext, applicationcontext, applicationcontextexception, beanfactorylocator, beansexception, classpathresource, configurablewebapplicationcontext, configurablewebapplicationcontext, illegalstateexception, io, servlet, servletcontext, string, string, util, webapplicationcontext, webapplicationcontext

The Spring Framework ContextLoader.java source code

/*
 * 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 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/**/*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"
	 */
	public static final String CONTEXT_CLASS_PARAM = "contextClass";

	/**
	 * Name of servlet context parameter (i.e., "<code>contextConfigLocation")
	 * 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")
	 * 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 classpath*:beanRefContext.xml,
	 * 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")
	 * 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 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.
			ApplicationContext parent = loadParentContext(servletContext);

			// Store context in local instance variable, to guarantee that
			// it is available on ServletContext shutdown.
			this.context = createWebApplicationContext(servletContext, parent);
			servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, this.context);
			currentContextPerThread.put(Thread.currentThread().getContextClassLoader(), this.context);

			if (logger.isDebugEnabled()) {
				logger.debug("Published root WebApplicationContext as ServletContext attribute with name [" +
						WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE + "]");
			}
			if (logger.isInfoEnabled()) {
				long elapsedTime = System.currentTimeMillis() - startTime;
				logger.info("Root WebApplicationContext: initialization completed in " + elapsedTime + " ms");
			}

			return this.context;
		}
		catch (RuntimeException ex) {
			logger.error("Context initialization failed", ex);
			servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, ex);
			throw ex;
		}
		catch (Error err) {
			logger.error("Context initialization failed", err);
			servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, err);
			throw err;
		}
	}

	/**
	 * Instantiate the root WebApplicationContext for this loader, either the
	 * default context class or a custom context class if specified.
	 * <p>This implementation expects custom contexts to implement the
	 * {@link ConfigurableWebApplicationContext} interface.
	 * Can be overridden in subclasses.
	 * <p>In addition, {@link #customizeContext} gets called prior to refreshing the
	 * context, allowing subclasses to perform custom modifications to the context.
	 * @param servletContext current servlet context
	 * @param parent the parent ApplicationContext to use, or <code>null if none
	 * @return the root WebApplicationContext
	 * @throws BeansException if the context couldn't be initialized
	 * @see ConfigurableWebApplicationContext
	 */
	protected WebApplicationContext createWebApplicationContext(
			ServletContext servletContext, ApplicationContext parent) throws BeansException {

		Class contextClass = determineContextClass(servletContext);
		if (!ConfigurableWebApplicationContext.class.isAssignableFrom(contextClass)) {
			throw new ApplicationContextException("Custom context class [" + contextClass.getName() +
					"] is not of type [" + ConfigurableWebApplicationContext.class.getName() + "]");
		}

		ConfigurableWebApplicationContext wac =
				(ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass);
		wac.setParent(parent);
		wac.setServletContext(servletContext);
		wac.setConfigLocation(servletContext.getInitParameter(CONFIG_LOCATION_PARAM));
		customizeContext(servletContext, wac);
		wac.refresh();

		return wac;
	}

	/**
	 * Return the WebApplicationContext implementation class to use, either the
	 * default XmlWebApplicationContext or a custom context class if specified.
	 * @param servletContext current servlet context
	 * @return the WebApplicationContext implementation class to use
	 * @throws ApplicationContextException if the context class couldn't be loaded
	 * @see #CONTEXT_CLASS_PARAM
	 * @see org.springframework.web.context.support.XmlWebApplicationContext
	 */
	protected Class determineContextClass(ServletContext servletContext) throws ApplicationContextException {
		String contextClassName = servletContext.getInitParameter(CONTEXT_CLASS_PARAM);
		if (contextClassName != null) {
			try {
				return ClassUtils.forName(contextClassName);
			}
			catch (ClassNotFoundException ex) {
				throw new ApplicationContextException(
						"Failed to load custom context class [" + contextClassName + "]", ex);
			}
		}
		else {
			contextClassName = defaultStrategies.getProperty(WebApplicationContext.class.getName());
			try {
				return ClassUtils.forName(contextClassName);
			}
			catch (ClassNotFoundException ex) {
				throw new ApplicationContextException(
						"Failed to load default context class [" + contextClassName + "]", ex);
			}
		}
	}

	/**
	 * Customize the {@link ConfigurableWebApplicationContext} created by this
	 * ContextLoader after config locations have been supplied to the context
	 * but before the context is <em>refreshed.
	 * <p>The default implementation is empty but can be overridden in subclasses
	 * to customize the application context.
	 * @param servletContext the current servlet context
	 * @param applicationContext the newly created application context
	 * @see #createWebApplicationContext(ServletContext, ApplicationContext)
	 */
	protected void customizeContext(
			ServletContext servletContext, ConfigurableWebApplicationContext applicationContext) {
	}

	/**
	 * Template method with default implementation (which may be overridden by a
	 * subclass), to load or obtain an ApplicationContext instance which will be
	 * used as the parent context of the root WebApplicationContext. If the
	 * return value from the method is null, no parent context is set.
	 * <p>The main reason to load a parent context here is to allow multiple root
	 * web application contexts to all be children of a shared EAR context, or
	 * alternately to also share the same parent context that is visible to
	 * EJBs. For pure web applications, there is usually no need to worry about
	 * having a parent context to the root web application context.
	 * <p>The default implementation uses
	 * {@link org.springframework.context.access.ContextSingletonBeanFactoryLocator},
	 * configured via {@link #LOCATOR_FACTORY_SELECTOR_PARAM} and
	 * {@link #LOCATOR_FACTORY_KEY_PARAM}, to load a parent context
	 * which will be shared by all other users of ContextsingletonBeanFactoryLocator
	 * which also use the same configuration parameters.
	 * @param servletContext current servlet context
	 * @return the parent application context, or <code>null if none
	 * @throws BeansException if the context couldn't be initialized
	 * @see org.springframework.context.access.ContextSingletonBeanFactoryLocator
	 */
	protected ApplicationContext loadParentContext(ServletContext servletContext)
			throws BeansException {

		ApplicationContext parentContext = null;
		String locatorFactorySelector = servletContext.getInitParameter(LOCATOR_FACTORY_SELECTOR_PARAM);
		String parentContextKey = servletContext.getInitParameter(LOCATOR_FACTORY_KEY_PARAM);

		if (parentContextKey != null) {
			// locatorFactorySelector may be null, indicating the default "classpath*:beanRefContext.xml"
			BeanFactoryLocator locator = ContextSingletonBeanFactoryLocator.getInstance(locatorFactorySelector);
			if (logger.isDebugEnabled()) {
				logger.debug("Getting parent context definition: using parent context key of '" +
						parentContextKey + "' with BeanFactoryLocator");
			}
			this.parentContextRef = locator.useBeanFactory(parentContextKey);
			parentContext = (ApplicationContext) this.parentContextRef.getFactory();
		}

		return parentContext;
	}

	/**
	 * Close Spring's web application context for the given servlet context. If
	 * the default {@link #loadParentContext(ServletContext)} implementation,
	 * which uses ContextSingletonBeanFactoryLocator, has loaded any shared
	 * parent context, release one reference to that shared parent context.
	 * <p>If overriding {@link #loadParentContext(ServletContext)}, you may have
	 * to override this method as well.
	 * @param servletContext the ServletContext that the WebApplicationContext runs in
	 */
	public void closeWebApplicationContext(ServletContext servletContext) {
		servletContext.log("Closing Spring root WebApplicationContext");
		try {
			if (this.context instanceof ConfigurableWebApplicationContext) {
				((ConfigurableWebApplicationContext) this.context).close();
			}
		}
		finally {
			currentContextPerThread.remove(Thread.currentThread().getContextClassLoader());
			servletContext.removeAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE);
			if (this.parentContextRef != null) {
				this.parentContextRef.release();
			}
		}
	}


	/**
	 * Obtain the Spring root web application context for the current thread
	 * (i.e. for the current thread's context ClassLoader, which needs to be
	 * the web application's ClassLoader).
	 * @return the current root web application context, or <code>null
	 * if none found
	 * @see org.springframework.web.context.support.SpringBeanAutowiringSupport
	 */
	public static WebApplicationContext getCurrentWebApplicationContext() {
		return (WebApplicationContext) currentContextPerThread.get(Thread.currentThread().getContextClassLoader());
	}

}

Other Spring Framework examples (source code examples)

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