org.springframework.web.context

Class ContextLoader

java.lang.Object

org.springframework.web.context.ContextLoader

Direct Known Subclasses:

ContextLoaderListener

public class ContextLoader
extends Object

Performs the actual initialization work for the root application context. Called by ContextLoaderListener.

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 the ConfigurableWebApplicationContext interface.

Processes a "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").

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.

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.

As of Spring 3.1, ContextLoader supports injecting the root web application context via the ContextLoader(WebApplicationContext) constructor, allowing for programmatic configuration in Servlet 3.0+ environments. See WebApplicationInitializer for usage examples.

Since:

17.02.2003

Author:

Juergen Hoeller, Colin Sampaleanu, Sam Brannen

See Also:

ContextLoaderListener, ConfigurableWebApplicationContext, XmlWebApplicationContext

Field Summary

Fields

Modifier and Type	Field and Description
static String	CONFIG_LOCATION_PARAM Name of servlet context parameter (i.e., "contextConfigLocation") 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	CONTEXT_ID_PARAM Config param for the root WebApplicationContext id, to be used as serialization id for the underlying BeanFactory: "contextId"
static String	CONTEXT_INITIALIZER_CLASSES_PARAM Config param for which ApplicationContextInitializer classes to use for initializing the web application context: "contextInitializerClasses"
static String	LOCATOR_FACTORY_KEY_PARAM Optional servlet context parameter (i.e., "parentContextKey") 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 (i.e., "locatorFactorySelector") used only when obtaining a parent context using the default implementation of loadParentContext(ServletContext servletContext).

Constructor Summary

Constructors

Constructor and Description
ContextLoader() Create a new ContextLoader that will create a web application context based on the "contextClass" and "contextConfigLocation" servlet context-params.
ContextLoader(WebApplicationContext context) Create a new ContextLoader with the given application context.

Method Summary

Methods

Modifier and Type	Method and Description
void	closeWebApplicationContext(ServletContext servletContext) Close Spring's web application context for the given servlet context.
protected void	configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac, ServletContext sc)
protected WebApplicationContext	createWebApplicationContext(ServletContext sc) Instantiate the root WebApplicationContext for this loader, either the default context class or a custom context class if specified.
protected WebApplicationContext	createWebApplicationContext(ServletContext sc, ApplicationContext parent) Deprecated. as of Spring 3.1 in favor of createWebApplicationContext(ServletContext) and configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext, ServletContext)
protected void	customizeContext(ServletContext servletContext, ConfigurableWebApplicationContext applicationContext) Customize the ConfigurableWebApplicationContext created by this ContextLoader after config locations have been supplied to the context but before the context is refreshed.
protected Class<?>	determineContextClass(ServletContext servletContext) Return the WebApplicationContext implementation class to use, either the default XmlWebApplicationContext or a custom context class if specified.
protected List<Class<ApplicationContextInitializer<ConfigurableApplicationContext>>>	determineContextInitializerClasses(ServletContext servletContext) Return the ApplicationContextInitializer implementation classes to use if any have been specified by CONTEXT_INITIALIZER_CLASSES_PARAM.
static WebApplicationContext	getCurrentWebApplicationContext() Obtain the Spring root web application context for the current thread (i.e.
WebApplicationContext	initWebApplicationContext(ServletContext servletContext) Initialize Spring's web application context for the given servlet context, using the application context provided at construction time, or creating a new one 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:

determineContextClass(ServletContext), createWebApplicationContext(ServletContext, ApplicationContext), Constant Field Values

CONTEXT_ID_PARAM

public static final String CONTEXT_ID_PARAM

Config param for the root WebApplicationContext id, to be used as serialization id for the underlying BeanFactory: "contextId"

See Also:

Constant Field Values

CONTEXT_INITIALIZER_CLASSES_PARAM

public static final String CONTEXT_INITIALIZER_CLASSES_PARAM

Config param for which ApplicationContextInitializer classes to use for initializing the web application context: "contextInitializerClasses"

See Also:

customizeContext(ServletContext, ConfigurableWebApplicationContext), Constant Field Values

CONFIG_LOCATION_PARAM

public static final String CONFIG_LOCATION_PARAM

Name of servlet context parameter (i.e., "contextConfigLocation") 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 (i.e., "locatorFactorySelector") 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, which is used to obtain the BeanFactoryLocator instance from which the parent context is obtained.

The default is classpath*:beanRefContext.xml, matching the default applied for the ContextSingletonBeanFactoryLocator.getInstance() method. Supplying the "parentContextKey" parameter is sufficient in this case.

See Also:

Constant Field Values

LOCATOR_FACTORY_KEY_PARAM

public static final String LOCATOR_FACTORY_KEY_PARAM

Optional servlet context parameter (i.e., "parentContextKey") 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, obtaining the parent application context from the BeanFactoryLocator instance.

Supplying this "parentContextKey" parameter is sufficient when relying on the default classpath*:beanRefContext.xml selector for candidate factory references.

See Also:

Constant Field Values

Constructor Detail

ContextLoader

public ContextLoader()

Create a new ContextLoader that will create a web application context based on the "contextClass" and "contextConfigLocation" servlet context-params. See class-level documentation for details on default values for each.

This constructor is typically used when declaring the ContextLoaderListener subclass as a <listener> within web.xml, as a no-arg constructor is required.

The created application context will be registered into the ServletContext under the attribute name WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE and subclasses are free to call the closeWebApplicationContext(javax.servlet.ServletContext) method on container shutdown to close the application context.

See Also:

ContextLoader(WebApplicationContext), initWebApplicationContext(ServletContext), closeWebApplicationContext(ServletContext)

ContextLoader

public ContextLoader(WebApplicationContext context)

Create a new ContextLoader with the given application context. This constructor is useful in Servlet 3.0+ environments where instance-based registration of listeners is possible through the ServletContext.addListener(java.lang.String) API.

The context may or may not yet be refreshed. If it (a) is an implementation of ConfigurableWebApplicationContext and (b) has not already been refreshed (the recommended approach), then the following will occur:

• If the given context has not already been assigned an id, one will be assigned to it
• ServletContext and ServletConfig objects will be delegated to the application context
• customizeContext(javax.servlet.ServletContext, org.springframework.web.context.ConfigurableWebApplicationContext) will be called
• Any ApplicationContextInitializers specified through the "contextInitializerClasses" init-param will be applied.
• refresh() will be called

If the context has already been refreshed or does not implement ConfigurableWebApplicationContext, none of the above will occur under the assumption that the user has performed these actions (or not) per his or her specific needs.

See WebApplicationInitializer for usage examples.

In any case, the given application context will be registered into the ServletContext under the attribute name WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE and subclasses are free to call the closeWebApplicationContext(javax.servlet.ServletContext) method on container shutdown to close the application context.

Parameters:

context - the application context to manage

See Also:

initWebApplicationContext(ServletContext), closeWebApplicationContext(ServletContext)

Method Detail

initWebApplicationContext

public WebApplicationContext initWebApplicationContext(ServletContext servletContext)

Initialize Spring's web application context for the given servlet context, using the application context provided at construction time, or creating a new one according to the "contextClass" and "contextConfigLocation" context-params.

Parameters:

servletContext - current servlet context

Returns:

the new WebApplicationContext

See Also:

ContextLoader(WebApplicationContext), CONTEXT_CLASS_PARAM, CONFIG_LOCATION_PARAM

createWebApplicationContext

protected WebApplicationContext createWebApplicationContext(ServletContext sc)

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 the ConfigurableWebApplicationContext interface. Can be overridden in subclasses.

In addition, customizeContext(javax.servlet.ServletContext, org.springframework.web.context.ConfigurableWebApplicationContext) gets called prior to refreshing the context, allowing subclasses to perform custom modifications to the context.

Parameters:

sc - current servlet context

Returns:

the root WebApplicationContext

See Also:

ConfigurableWebApplicationContext

createWebApplicationContext

@Deprecated
protected WebApplicationContext createWebApplicationContext(ServletContext sc,
                                                           ApplicationContext parent)

Deprecated. as of Spring 3.1 in favor of createWebApplicationContext(ServletContext) and configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext, ServletContext)

configureAndRefreshWebApplicationContext

protected void configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac,
                                            ServletContext sc)

determineContextClass

protected Class<?> determineContextClass(ServletContext servletContext)

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

See Also:

CONTEXT_CLASS_PARAM, XmlWebApplicationContext

determineContextInitializerClasses

protected List<Class<ApplicationContextInitializer<ConfigurableApplicationContext>>> determineContextInitializerClasses(ServletContext servletContext)

Return the ApplicationContextInitializer implementation classes to use if any have been specified by CONTEXT_INITIALIZER_CLASSES_PARAM.

Parameters:

servletContext - current servlet context

See Also:

CONTEXT_INITIALIZER_CLASSES_PARAM

customizeContext

protected void customizeContext(ServletContext servletContext,
                    ConfigurableWebApplicationContext applicationContext)

Customize the ConfigurableWebApplicationContext created by this ContextLoader after config locations have been supplied to the context but before the context is refreshed.

The default implementation determines what (if any) context initializer classes have been specified through context init parameters and invokes each with the given web application context.

Any ApplicationContextInitializers implementing Ordered or marked with @Order will be sorted appropriately.

Parameters:

servletContext - the current servlet context

applicationContext - the newly created application context

See Also:

createWebApplicationContext(ServletContext, ApplicationContext), CONTEXT_INITIALIZER_CLASSES_PARAM, ApplicationContextInitializer.initialize(ConfigurableApplicationContext)

loadParentContext

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. 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

See Also:

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.

Parameters:

servletContext - the ServletContext that the WebApplicationContext runs in

getCurrentWebApplicationContext

public static WebApplicationContext getCurrentWebApplicationContext()

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).

Returns:

the current root web application context, or null if none found

See Also:

SpringBeanAutowiringSupport