org.springframework.web.struts
Class ContextLoaderPlugIn

java.lang.Object
  org.springframework.web.struts.ContextLoaderPlugIn

All Implemented Interfaces:

org.apache.struts.action.PlugIn

public class ContextLoaderPlugIn

extends java.lang.Object

implements org.apache.struts.action.PlugIn

Struts 1.1 PlugIn that loads a Spring application context for the Struts ActionServlet. This context will automatically refer to the root WebApplicationContext (loaded by ContextLoaderListener/Servlet) as parent.

The default namespace of the WebApplicationContext is the name of the Struts ActionServlet, suffixed with "-servlet" (e.g. "action-servlet"). The default location of the XmlWebApplicationContext configuration file is therefore "/WEB-INF/action-servlet.xml".

 <plug-in className="org.springframework.web.struts.ContextLoaderPlugIn"/>

The location of the context configuration files can be customized through the "contextConfigLocation" setting, analogous to the root WebApplicationContext and FrameworkServlet contexts.

 <plug-in className="org.springframework.web.struts.ContextLoaderPlugIn">
   <set-property property="contextConfigLocation" value="/WEB-INF/action-servlet.xml,/WEB-INF/myContext.xml"/>
 </plug-in>

Beans defined in the ContextLoaderPlugin context can be accessed from conventional Struts Actions, via fetching the WebApplicationContext reference from the ServletContext. ActionSupport and DispatchActionSupport are pre-built convenience classes that provide easy access to the context.

It is normally preferable to access Spring's root WebApplicationContext in such scenarios, though: A shared middle tier should be defined there rather than in a ContextLoaderPlugin context, for access by any web component. ActionSupport and DispatchActionSupport auto-detect the root context too.

A special usage of this PlugIn is to define Struts Actions themselves as beans, typically wiring them with middle tier components defined in the root context. Such Actions will then be delegated to by proxy definitions in the Struts configuration, using the DelegatingActionProxy class.

Note: The idea of delegating to Spring-managed Struts Actions originated in Don Brown's Spring Struts Plugin. ContextLoaderPlugIn and DelegatingActionProxy constitute a clean-room implementation of the same idea, essentially superseding the original plugin. Many thanks to Don Brown and Matt Raible for the original work, and for the agreement to reimplement the idea in standard Spring!

Since:

05.04.2004

Author:

Juergen Hoeller

See Also:

SERVLET_CONTEXT_ATTRIBUTE, ActionSupport, DispatchActionSupport, DelegatingActionProxy, DelegatingRequestProcessor, DelegatingTilesRequestProcessor, ContextLoaderListener, ContextLoaderServlet, FrameworkServlet

Field Summary

static java.lang.Class	DEFAULT_CONTEXT_CLASS Default context class for ContextLoaderPlugIn.
static java.lang.String	DEFAULT_NAMESPACE_SUFFIX Suffix for WebApplicationContext namespaces.
protected org.apache.commons.logging.Log	logger
static java.lang.String	SERVLET_CONTEXT_ATTRIBUTE Name of the ServletContext attribute for the WebApplicationContext

Constructor Summary

ContextLoaderPlugIn()

Method Summary

protected WebApplicationContext	createWebApplicationContext(WebApplicationContext parent) Instantiate the WebApplicationContext for the ActionServlet, either a default XmlWebApplicationContext or a custom context class if set.
void	destroy() Close the WebApplicationContext of the ActionServlet.
org.apache.struts.action.ActionServlet	getActionServlet() Return the ActionServlet that this PlugIn is associated with.
java.lang.Class	getContextClass() Return the custom context class.
java.lang.String	getContextConfigLocation() Return the explicit context config location, if any.
java.lang.String	getNamespace() Return the namespace for the ActionServlet, falling back to default scheme if no custom namespace was set: e.g.
WebApplicationContext	getWebApplicationContext() Return the ActionServlet's WebApplicationContext.
void	init(org.apache.struts.action.ActionServlet actionServlet, org.apache.struts.config.ModuleConfig moduleConfig) Create the ActionServlet's WebApplicationContext.
protected WebApplicationContext	initWebApplicationContext() Initialize and publish the WebApplicationContext for the ActionServlet.
protected void	onInit() Callback for custom initialization after the context has been set up.
void	setContextClass(java.lang.Class contextClass) Set a custom context class.
void	setContextClassName(java.lang.String contextClassName) Set a custom context class by name.
void	setContextConfigLocation(java.lang.String contextConfigLocation) Set the context config location explicitly, instead of relying on the default location built from the namespace.
void	setNamespace(java.lang.String namespace) Set a custom namespace for the ActionServlet, to be used for building a default context config location.

Methods inherited from class java.lang.Object

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

Field Detail

DEFAULT_NAMESPACE_SUFFIX

public static final java.lang.String DEFAULT_NAMESPACE_SUFFIX

Suffix for WebApplicationContext namespaces. If a Struts ActionServlet is given the name "action" in a context, the namespace used by this PlugIn will resolve to "action-servlet".

See Also:

Constant Field Values

DEFAULT_CONTEXT_CLASS

public static final java.lang.Class DEFAULT_CONTEXT_CLASS

Default context class for ContextLoaderPlugIn.

See Also:

XmlWebApplicationContext

SERVLET_CONTEXT_ATTRIBUTE

public static final java.lang.String SERVLET_CONTEXT_ATTRIBUTE

Name of the ServletContext attribute for the WebApplicationContext

logger

protected final org.apache.commons.logging.Log logger

Constructor Detail

ContextLoaderPlugIn

public ContextLoaderPlugIn()

Method Detail

setContextClassName

public void setContextClassName(java.lang.String contextClassName)
                         throws java.lang.ClassNotFoundException

Set a custom context class by name. This class must be of type WebApplicationContext, when using the default ContextLoaderPlugIn implementation, the context class must also implement ConfigurableWebApplicationContext.

Throws:

java.lang.ClassNotFoundException

See Also:

createWebApplicationContext(org.springframework.web.context.WebApplicationContext)

setContextClass

public void setContextClass(java.lang.Class contextClass)

Set a custom context class. This class must be of type WebApplicationContext, when using the default ContextLoaderPlugIn implementation, the context class must also implement ConfigurableWebApplicationContext.

See Also:

createWebApplicationContext(org.springframework.web.context.WebApplicationContext)

getContextClass

public java.lang.Class getContextClass()

Return the custom context class.

setNamespace

public void setNamespace(java.lang.String namespace)

Set a custom namespace for the ActionServlet, to be used for building a default context config location.

getNamespace

public java.lang.String getNamespace()

Return the namespace for the ActionServlet, falling back to default scheme if no custom namespace was set: e.g. "test-servlet" for a servlet named "test".

setContextConfigLocation

public void setContextConfigLocation(java.lang.String contextConfigLocation)

Set the context config location explicitly, instead of relying on the default location built from the namespace. This location string can consist of multiple locations separated by any number of commas and spaces.

getContextConfigLocation

public java.lang.String getContextConfigLocation()

Return the explicit context config location, if any.

init

public final void init(org.apache.struts.action.ActionServlet actionServlet,
                       org.apache.struts.config.ModuleConfig moduleConfig)
                throws javax.servlet.ServletException

Create the ActionServlet's WebApplicationContext.

Specified by:

init in interface org.apache.struts.action.PlugIn

Throws:

javax.servlet.ServletException

initWebApplicationContext

protected WebApplicationContext initWebApplicationContext()
                                                   throws BeansException

Initialize and publish the WebApplicationContext for the ActionServlet. Delegates to createWebApplicationContext for actual creation. Can be overridden in subclasses.

Throws:

BeansException - if the context couldn't be initialized

See Also:

createWebApplicationContext(org.springframework.web.context.WebApplicationContext)

createWebApplicationContext

protected WebApplicationContext createWebApplicationContext(WebApplicationContext parent)
                                                     throws BeansException

Instantiate the WebApplicationContext for the ActionServlet, either a default XmlWebApplicationContext or a custom context class if set. This implementation expects custom contexts to implement ConfigurableWebApplicationContext. Can be overridden in subclasses.

Throws:

BeansException - if the context couldn't be initialized

See Also:

setContextClass(java.lang.Class), XmlWebApplicationContext

getActionServlet

public final org.apache.struts.action.ActionServlet getActionServlet()

Return the ActionServlet that this PlugIn is associated with.

getWebApplicationContext

public final WebApplicationContext getWebApplicationContext()

Return the ActionServlet's WebApplicationContext.

onInit

protected void onInit()
               throws javax.servlet.ServletException

Callback for custom initialization after the context has been set up.

Throws:

javax.servlet.ServletException - if initialization failed

destroy

public void destroy()

Close the WebApplicationContext of the ActionServlet.

Specified by:

destroy in interface org.apache.struts.action.PlugIn

See Also:

ConfigurableApplicationContext.close()