org.springframework.web.context.ContextLoader Maven / Gradle / Ivy
/*
* Copyright 2002-2007 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.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.io.ClassPathResource;
import org.springframework.core.io.support.PropertiesLoaderUtils;
import org.springframework.util.ClassUtils;
import org.springframework.util.StringUtils;
import org.springframework.web.context.support.XmlWebApplicationContext;
/**
* Performs the actual initialization work for the root application context.
* Called by {@link ContextLoaderListener} and {@link ContextLoaderServlet}.
*
* Looks for a "contextClass" parameter at the web.xml context-param level
* to specify the context class type, falling back to the default of
* {@link XmlWebApplicationContext} if not found. With the default ContextLoader
* implementation, any context class specified needs to implement
* ConfigurableWebApplicationContext.
*
*
Passes a "contextConfigLocation" context-param to the context instance,
* parsing it into potentially multiple file paths which can be separated by
* any number of commas and spaces, like "applicationContext1.xml,
* applicationContext2.xml". If not explicitly specified, the context
* implementation is supposed to use a default location (with
* XmlWebApplicationContext: "/WEB-INF/applicationContext.xml").
*
*
Note: In case of multiple config locations, later bean definitions will
* override ones defined in earlier 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.
*
*
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
* @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: "contextClass"
*/
public static final String CONTEXT_CLASS_PARAM = "contextClass";
/**
* Name of servlet context parameter 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 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 used to obtain the BeanFactoryLocator instance from which the
* parent context is obtained.
*
This will normally be set to classpath*:beanRefContext.xml
* to match the default applied for the
* {@link ContextSingletonBeanFactoryLocator#getInstance()} method.
*/
public static final String LOCATOR_FACTORY_SELECTOR_PARAM = "locatorFactorySelector";
/**
* Optional servlet context parameter 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
* used to obtain the parent application context from the BeanFactoryLocator
* instance.
*/
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 final Log logger = LogFactory.getLog(ContextLoader.class);
/**
* The root WebApplicationContext instance that this loaded 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 "contextClass" and "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);
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.
*
This implementation expects custom contexts to implement
* ConfigurableWebApplicationContext. Can be overridden in subclasses.
* @param servletContext current servlet context
* @param parent the parent ApplicationContext to use, or 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);
String configLocation = servletContext.getInitParameter(CONFIG_LOCATION_PARAM);
if (configLocation != null) {
wac.setConfigLocations(StringUtils.tokenizeToStringArray(configLocation,
ConfigurableWebApplicationContext.CONFIG_LOCATION_DELIMITERS));
}
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);
}
}
}
/**
* 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.
*
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.
*
The default implementation uses 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 null if none
* @throws BeansException if the context couldn't be initialized
* @see org.springframework.beans.factory.access.BeanFactoryLocator
* @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 (locatorFactorySelector != null) {
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.
*
If overriding {@link #loadParentContext(ServletContext)}, you may have
* to override this method as well.
*/
public void closeWebApplicationContext(ServletContext servletContext) {
servletContext.log("Closing Spring root WebApplicationContext");
try {
if (this.context instanceof ConfigurableWebApplicationContext) {
((ConfigurableWebApplicationContext) this.context).close();
}
}
finally {
if (this.parentContextRef != null) {
this.parentContextRef.release();
}
}
}
}