org.apache.commons.chain.web
Class ChainListener

java.lang.Object
  org.apache.commons.chain.web.ChainListener

All Implemented Interfaces:

EventListener, ServletContextListener

public class ChainListener
extends Object
implements ServletContextListener

ServletContextListener that automatically scans chain configuration files in the current web application at startup time, and exposes the result in a Catalog under a specified servlet context attribute. The following context init parameters are utilized:

• org.apache.commons.chain.CONFIG_CLASS_RESOURCE - comma-delimited list of chain configuration resources to be loaded via ClassLoader.getResource() calls. If not specified, no class loader resources will be loaded.
• org.apache.commons.chain.CONFIG_WEB_RESOURCE - comma-delimited list of chain configuration webapp resources to be loaded. If not specified, no web application resources will be loaded.
• org.apache.commons.chain.CONFIG_ATTR - Name of the servlet context attribute under which the resulting Catalog will be created or updated. If not specified, it is expected that parsed resources will contain <catalog> elements (which will cause registration of the created Catalogs into the CatalogFactory for this application, and no servet context attribute will be created. NOTE - This parameter is deprecated.

• org.apache.commons.chain.RULE_SET - Fully qualified class name of a Digester RuleSet implementation to use for parsing configuration resources (this class must have a public zero-args constructor). If not defined, the standard RuleSet implementation will be used.

When a web application that has configured this listener is started, it will acquire the Catalog under the specified servlet context attribute key, creating a new one if there is none already there. This Catalog will then be populated by scanning configuration resources from the following sources (loaded in this order):

• Resources loaded from any META-INF/chain-config.xml resource found in a JAR file in /WEB-INF/lib.
• Resources loaded from specified resource paths from the webapp's class loader (via ClassLoader.getResource()).
• Resources loaded from specified resource paths in the web application archive (via ServetContext.getResource()).

If no attribute key is specified, on the other hand, parsed configuration resources are expected to contain <catalog> elements, and the catalogs will be registered with the CatalogFactory for this web application.

This class requires Servlet 2.3 or later. If you are running on Servlet 2.2 system, consider using ChainServlet instead. Note that ChainServlet uses parameters of the same names, but they are servlet init parameters instead of context init parameters. Because of this, you can use both facilities in the same application, if desired.

Version:

$Revision: 658426 $ $Date: 2008-05-20 21:55:38 +0100 (Tue, 20 May 2008) $

Author:

Craig R. McClanahan, Ted Husted

Field Summary

static String	CONFIG_ATTR The name of the context init parameter containing the name of the servlet context attribute under which our resulting Catalog will be stored.
static String	CONFIG_CLASS_RESOURCE The name of the context init parameter containing a comma-delimited list of class loader resources to be scanned.
static String	CONFIG_WEB_RESOURCE The name of the context init parameter containing a comma-delimited list of web applicaton resources to be scanned.
static String	RULE_SET The name of the context init parameter containing the fully qualified class name of the RuleSet implementation for configuring our ConfigParser.

Constructor Summary

ChainListener()

Method Summary

void	contextDestroyed(ServletContextEvent event) Remove the configured Catalog from the servlet context attributes for this web application.
void	contextInitialized(ServletContextEvent event) Scan the required chain configuration resources, assemble the configured chains into a Catalog, and expose it as a servlet context attribute under the specified key.

Methods inherited from class java.lang.Object

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

Field Detail

CONFIG_ATTR

public static final String CONFIG_ATTR

The name of the context init parameter containing the name of the servlet context attribute under which our resulting Catalog will be stored.

See Also:

Constant Field Values

CONFIG_CLASS_RESOURCE

public static final String CONFIG_CLASS_RESOURCE

The name of the context init parameter containing a comma-delimited list of class loader resources to be scanned.

See Also:

Constant Field Values

CONFIG_WEB_RESOURCE

public static final String CONFIG_WEB_RESOURCE

The name of the context init parameter containing a comma-delimited list of web applicaton resources to be scanned.

See Also:

Constant Field Values

RULE_SET

public static final String RULE_SET

The name of the context init parameter containing the fully qualified class name of the RuleSet implementation for configuring our ConfigParser.

See Also:

Constant Field Values

Constructor Detail

ChainListener

public ChainListener()

Method Detail

contextDestroyed

public void contextDestroyed(ServletContextEvent event)

Remove the configured Catalog from the servlet context attributes for this web application.

Specified by:

contextDestroyed in interface ServletContextListener

Parameters:

event - ServletContextEvent to be processed

contextInitialized

public void contextInitialized(ServletContextEvent event)

Scan the required chain configuration resources, assemble the configured chains into a Catalog, and expose it as a servlet context attribute under the specified key.

Specified by:

contextInitialized in interface ServletContextListener

Parameters:

event - ServletContextEvent to be processed