org.springframework.web.context
Class ContextLoader

java.lang.Object
  extended by 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.

Since:
17.02.2003
Author:
Juergen Hoeller, Colin Sampaleanu, Sam Brannen
See Also:
ContextLoaderListener, ConfigurableWebApplicationContext, XmlWebApplicationContext

Field Summary
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_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
ContextLoader()
           
 
Method Summary
 void closeWebApplicationContext(ServletContext servletContext)
          Close Spring's web application context for the given servlet context.
protected  WebApplicationContext createWebApplicationContext(ServletContext sc, ApplicationContext parent)
          Instantiate the root WebApplicationContext for this loader, either the default context class or a custom context class if specified.
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, 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_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()
Method Detail

initWebApplicationContext

public WebApplicationContext initWebApplicationContext(ServletContext servletContext)
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
See Also:
CONTEXT_CLASS_PARAM, CONFIG_LOCATION_PARAM

createWebApplicationContext

protected WebApplicationContext createWebApplicationContext(ServletContext sc,
                                                            ApplicationContext parent)
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
parent - the parent ApplicationContext to use, or null if none
Returns:
the root WebApplicationContext
See Also:
ConfigurableWebApplicationContext

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 Ordered ApplicationContextInitializer 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