org.apache.commons.chain.web
Class ChainServlet

java.lang.Object
  javax.servlet.GenericServlet
      javax.servlet.http.HttpServlet
          org.apache.commons.chain.web.ChainServlet

All Implemented Interfaces:

Serializable, Servlet, ServletConfig

Direct Known Subclasses:

ChainProcessor

public class ChainServlet
extends HttpServlet

Servlet 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 servlet 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 servlet 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 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 runs on Servlet 2.2 or later. If you are running on a Servlet 2.3 or later system, you should also consider using ChainListener to initialize your Catalog. Note that ChainListener uses parameters of the same names, but they are context init parameters instead of servlet init parameters. Because of this, you can use both facilities in the same application, if desired.

Author:

Matthew J. Sgarlata, Craig R. McClanahan, Ted Husted

See Also:

Serialized Form

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

ChainServlet()

Method Summary

void	destroy() Clean up after ourselves as this application shuts down.
void	init() Create (if necessary) and configure a Catalog from the servlet init parameters that have been specified.
void	service(HttpServletRequest request, HttpServletResponse response) Does nothing; this servlet's only purpose is to initialize a Chain and store it in the servlet context.

Methods inherited from class javax.servlet.http.HttpServlet

doDelete, doGet, doHead, doOptions, doPost, doPut, doTrace, getLastModified, service

Methods inherited from class javax.servlet.GenericServlet

getInitParameter, getInitParameterNames, getServletConfig, getServletContext, getServletInfo, getServletName, init, log, log

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

ChainServlet

public ChainServlet()

Method Detail

destroy

public void destroy()

Clean up after ourselves as this application shuts down.

Specified by:

destroy in interface Servlet

Overrides:

destroy in class GenericServlet

init

public void init()
          throws ServletException

Create (if necessary) and configure a Catalog from the servlet init parameters that have been specified.

Overrides:

init in class GenericServlet

Throws:

ServletException - if the servlet could not be initialized

service

public void service(HttpServletRequest request,
                    HttpServletResponse response)
             throws ServletException,
                    IOException

Does nothing; this servlet's only purpose is to initialize a Chain and store it in the servlet context.

Overrides:

service in class HttpServlet

Parameters:

request - the request issued by the client

response - the response to be returned to the cliengt

Throws:

ServletException - (this exception is never thrown)

IOException - (this exception is never thrown)