ContextLoader (Spring Framework API 2.1) - Spring Framework 2.1.0 API 文档英文版

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org.springframework.web.context
Class ContextLoader

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

public class ContextLoader
extends Object
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 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.

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 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)
                                                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:: 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