org.apache.commons.chain.web: public class: ChainServlet

org.apache.commons.chain.web
public class: ChainServlet [javadoc | source]

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

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 Catalog s 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

author: Craig - R. McClanahan

author: Ted - Husted

Field Summary
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.
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.
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.
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 .

Method from org.apache.commons.chain.web.ChainServlet Summary:
destroy, init, service

Methods from javax.servlet.http.HttpServlet:
service

Methods from javax.servlet.GenericServlet:
destroy, getInitParameter, getInitParameterNames, getServletConfig, getServletContext, getServletInfo, getServletName, init, init, log, log, service

Methods from java.lang.Object:
equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method from org.apache.commons.chain.web.ChainServlet Detail:
public void destroy() { // --------------------------------------------------------- Servlet Methods ServletConfig config = getServletConfig(); ServletContext context = getServletContext(); String attr = config.getInitParameter(CONFIG_ATTR); if (attr != null) { context.removeAttribute(attr); } CatalogFactory.clear(); } Clean up after ourselves as this application shuts down.
public void init() throws ServletException { Log log = LogFactory.getLog(ChainServlet.class); ServletConfig config = getServletConfig(); ServletContext context = getServletContext(); if (log.isInfoEnabled()) { log.info("Initializing chain servlet '" + config.getServletName() + "'"); } // Retrieve servlet init parameters that we need String attr = config.getInitParameter(CONFIG_ATTR); String classResources = context.getInitParameter(CONFIG_CLASS_RESOURCE); String ruleSet = context.getInitParameter(RULE_SET); String webResources = context.getInitParameter(CONFIG_WEB_RESOURCE); // Retrieve or create the Catalog instance we may be updating Catalog catalog = null; if (attr != null) { catalog = (Catalog) context.getAttribute(attr); if (catalog == null) { catalog = new CatalogBase(); } } // Construct the configuration resource parser we will use ConfigParser parser = new ConfigParser(); if (ruleSet != null) { try { ClassLoader loader = Thread.currentThread().getContextClassLoader(); if (loader == null) { loader = this.getClass().getClassLoader(); } Class clazz = loader.loadClass(ruleSet); parser.setRuleSet((RuleSet) clazz.newInstance()); } catch (Exception e) { throw new ServletException("Exception initalizing RuleSet '" + ruleSet + "' instance", e); } } // Parse the resources specified in our init parameters (if any) if (attr == null) { ChainResources.parseClassResources (classResources, parser); ChainResources.parseWebResources (context, webResources, parser); } else { ChainResources.parseClassResources (catalog, classResources, parser); ChainResources.parseWebResources (catalog, context, webResources, parser); } // Expose the completed catalog (if requested) if (attr != null) { context.setAttribute(attr, catalog); } } Create (if necessary) and configure a Catalog from the servlet init parameters that have been specified.
public void service(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException { // do nothing } Does nothing; this servlet's only purpose is to initialize a Chain and store it in the servlet context.

Method from org.apache.commons.chain.web.ChainServlet Detail:

 public  void destroy() {
    // --------------------------------------------------------- Servlet Methods
        ServletConfig config = getServletConfig();
        ServletContext context = getServletContext();
        String attr = config.getInitParameter(CONFIG_ATTR);
        if (attr != null) {
            context.removeAttribute(attr);
        }
        CatalogFactory.clear();
}

Clean up after ourselves as this application shuts down.

 public  void init() throws ServletException {
        Log log = LogFactory.getLog(ChainServlet.class);
        ServletConfig config = getServletConfig();
        ServletContext context = getServletContext();
        if (log.isInfoEnabled()) {
            log.info("Initializing chain servlet '"
                     + config.getServletName() + "'");
        }
        // Retrieve servlet init parameters that we need
        String attr = config.getInitParameter(CONFIG_ATTR);
        String classResources =
            context.getInitParameter(CONFIG_CLASS_RESOURCE);
        String ruleSet = context.getInitParameter(RULE_SET);
        String webResources = context.getInitParameter(CONFIG_WEB_RESOURCE);
        // Retrieve or create the Catalog instance we may be updating
        Catalog catalog = null;
        if (attr != null) {
            catalog = (Catalog) context.getAttribute(attr);
            if (catalog == null) {
                catalog = new CatalogBase();
            }
        }
        // Construct the configuration resource parser we will use
        ConfigParser parser = new ConfigParser();
        if (ruleSet != null) {
            try {
                ClassLoader loader =
                    Thread.currentThread().getContextClassLoader();
                if (loader == null) {
                    loader = this.getClass().getClassLoader();
                }
                Class clazz = loader.loadClass(ruleSet);
                parser.setRuleSet((RuleSet) clazz.newInstance());
            } catch (Exception e) {
                throw new ServletException("Exception initalizing RuleSet '"
                                           + ruleSet + "' instance", e);
            }
        }
        // Parse the resources specified in our init parameters (if any)
        if (attr == null) {
            ChainResources.parseClassResources
                (classResources, parser);
            ChainResources.parseWebResources
                (context, webResources, parser);
        } else {
            ChainResources.parseClassResources
                (catalog, classResources, parser);
            ChainResources.parseWebResources
                (catalog, context, webResources, parser);
        }
        // Expose the completed catalog (if requested)
        if (attr != null) {
            context.setAttribute(attr, catalog);
        }
}

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

 public  void service(HttpServletRequest request,
    HttpServletResponse response) throws IOException, ServletException {
          // do nothing
}

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