org.springframework.web.context
Class ContextLoader

java.lang.Object
  org.springframework.web.context.ContextLoader

public class ContextLoader
extends Object

Performs the actual initialization work for the root application context. Called by ContextLoaderListener and 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 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 loadParentContext(ServletContext) method for more information.

Since:

17.02.2003

Author:

Juergen Hoeller, Colin Sampaleanu

See Also:

ContextLoaderListener, ContextLoaderServlet, ConfigurableWebApplicationContext, XmlWebApplicationContext

Field Summary

static String	CONFIG_LOCATION_PARAM Name of servlet context parameter that can specify the config location for the root context, falling back to the implementation's default otherwise.
static String	CONTEXT_CLASS_PARAM Config param for the root WebApplicationContext implementation class to use: "contextClass"
static String	LOCATOR_FACTORY_KEY_PARAM Optional servlet context parameter used only when obtaining a parent context using the default implementation of loadParentContext(ServletContext servletContext).
static String	LOCATOR_FACTORY_SELECTOR_PARAM Optional servlet context parameter used only when obtaining a parent context using the default implementation of loadParentContext(ServletContext servletContext).

Constructor Summary

ContextLoader()

Method Summary

void	closeWebApplicationContext(ServletContext servletContext) Close Spring's web application context for the given servlet context.
protected WebApplicationContext	createWebApplicationContext(ServletContext servletContext, ApplicationContext parent) Instantiate the root WebApplicationContext for this loader, either the default context class or a custom context class if specified.
protected Class	determineContextClass(ServletContext servletContext) Return the WebApplicationContext implementation class to use, either the default XmlWebApplicationContext or a custom context class if specified.
WebApplicationContext	initWebApplicationContext(ServletContext servletContext) Initialize Spring's web application context for the given servlet context, according to the "contextClass" and "contextConfigLocation" context-params.
protected ApplicationContext	loadParentContext(ServletContext servletContext) 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.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

CONTEXT_CLASS_PARAM

public static final String CONTEXT_CLASS_PARAM

Config param for the root WebApplicationContext implementation class to use: "contextClass"

See Also:

Constant Field Values

CONFIG_LOCATION_PARAM

public static final String CONFIG_LOCATION_PARAM

Name of servlet context parameter that can specify the config location for the root context, falling back to the implementation's default otherwise.

See Also:

XmlWebApplicationContext.DEFAULT_CONFIG_LOCATION, Constant Field Values

LOCATOR_FACTORY_SELECTOR_PARAM

public static final String LOCATOR_FACTORY_SELECTOR_PARAM

Optional servlet context parameter used only when obtaining a parent context using the default implementation of loadParentContext(ServletContext servletContext). Specifies the 'selector' used in the 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 ContextSingletonBeanFactoryLocator.getInstance() method.

See Also:

Constant Field Values

LOCATOR_FACTORY_KEY_PARAM

public static final String LOCATOR_FACTORY_KEY_PARAM

Optional servlet context parameter used only when obtaining a parent context using the default implementation of loadParentContext(ServletContext servletContext). Specifies the 'factoryKey' used in the BeanFactoryLocator.useBeanFactory(String factoryKey) method call used to obtain the parent application context from the BeanFactoryLocator instance.

See Also:

Constant Field Values

Constructor Detail

ContextLoader

public ContextLoader()

Method Detail

initWebApplicationContext

public WebApplicationContext initWebApplicationContext(ServletContext servletContext)
                                                throws IllegalStateException,
                                                       BeansException

Initialize Spring's web application context for the given servlet context, according to the "contextClass" and "contextConfigLocation" context-params.

Parameters:

servletContext - current servlet context

Returns:

the new WebApplicationContext

Throws:

IllegalStateException - if there is already a root application context present

BeansException - if the context failed to initialize

See Also:

CONTEXT_CLASS_PARAM, CONFIG_LOCATION_PARAM

createWebApplicationContext

protected WebApplicationContext createWebApplicationContext(ServletContext servletContext,
                                                            ApplicationContext parent)
                                                     throws BeansException

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.

Parameters:

servletContext - current servlet context

parent - the parent ApplicationContext to use, or null if none

Returns:

the root WebApplicationContext

Throws:

BeansException - if the context couldn't be initialized

See Also:

ConfigurableWebApplicationContext

determineContextClass

protected Class determineContextClass(ServletContext servletContext)
                               throws ApplicationContextException

Return the WebApplicationContext implementation class to use, either the default XmlWebApplicationContext or a custom context class if specified.

Parameters:

servletContext - current servlet context

Returns:

the WebApplicationContext implementation class to use

Throws:

ApplicationContextException - if the context class couldn't be loaded

See Also:

CONTEXT_CLASS_PARAM, XmlWebApplicationContext

loadParentContext

protected ApplicationContext loadParentContext(ServletContext servletContext)
                                        throws BeansException

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 LOCATOR_FACTORY_SELECTOR_PARAM and 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.

Parameters:

servletContext - current servlet context

Returns:

the parent application context, or null if none

Throws:

BeansException - if the context couldn't be initialized

See Also:

BeanFactoryLocator, ContextSingletonBeanFactoryLocator

closeWebApplicationContext

public void closeWebApplicationContext(ServletContext servletContext)

Close Spring's web application context for the given servlet context. If the default loadParentContext(ServletContext)implementation, which uses ContextSingletonBeanFactoryLocator, has loaded any shared parent context, release one reference to that shared parent context.

If overriding loadParentContext(ServletContext), you may have to override this method as well.