ChainServlet.java
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.commons.chain.web.jakarta;
import java.io.IOException;
import org.apache.commons.chain.Catalog;
import org.apache.commons.chain.CatalogFactory;
import org.apache.commons.chain.config.ConfigParser;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import jakarta.servlet.ServletConfig;
import jakarta.servlet.ServletContext;
import jakarta.servlet.ServletException;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
/**
* {@code Servlet} that automatically scans chain configuration files
* in the current web application at startup time, and exposes the result in a
* {@link Catalog} under a specified servlet context attribute. The following
* <em>servlet</em> init parameters are utilized:
* <ul>
* <li><strong>org.apache.commons.chain.CONFIG_CLASS_RESOURCE</strong> -
* comma-delimited list of chain configuration resources to be loaded
* via {@code ClassLoader.getResource()} calls. If not specified,
* no class loader resources will be loaded.</li>
* <li><strong>org.apache.commons.chain.CONFIG_WEB_RESOURCE</strong> -
* comma-delimited list of chain configuration webapp resources
* to be loaded. If not specified, no web application resources
* will be loaded.</li>
* <li><strong>org.apache.commons.chain.CONFIG_ATTR</strong> -
* Name of the servlet context attribute under which the
* resulting {@link Catalog} will be created or updated.
* If not specified, it is expected that parsed resources will
* contain {@code <catalog>} elements (which will
* cause registration of the created {@link Catalog}s into
* the {@link CatalogFactory} for this application, and no
* servet context attribute will be created.
* <strong>NOTE</strong> - This parameter is deprecated.</li>
* <li><strong>org.apache.commons.chain.RULE_SET</strong> -
* Fully qualified class name of a Digester {@code RuleSet}
* implementation to use for parsing configuration resources (this
* class must have a public zero-args constructor). If not defined,
* the standard {@code RuleSet} implementation will be used.</li>
* </ul>
*
* <p>When a web application that has configured this servlet is
* started, it will acquire the {@link Catalog} under the specified servlet
* context attribute key, creating a new one if there is none already there.
* This {@link Catalog} will then be populated by scanning configuration
* resources from the following sources (loaded in this order):</p>
* <ul>
* <li>Resources loaded from specified resource paths from the
* webapp's class loader (via {@code ClassLoader.getResource()}).</li>
* <li>Resources loaded from specified resource paths in the web application
* archive (via {@code ServetContext.getResource()}).</li>
* </ul>
*
* <p>If no attribute key is specified, on the other hand, parsed configuration
* resources are expected to contain {@code <catalog>} elements,
* and the catalogs will be registered with the {@link CatalogFactory}
* for this web application.</p>
*
* <p>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
* {@link ChainListener} to initialize your {@link Catalog}. Note that
* {@link ChainListener} uses parameters of the same names, but they are
* <em>context</em> init parameters instead of <em>servlet</em> init
* parameters. Because of this, you can use both facilities in the
* same application, if desired.</p>
*
* @author Matthew J. Sgarlata
* @author Craig R. McClanahan
* @author Ted Husted
*/
public class ChainServlet extends HttpServlet {
private static final long serialVersionUID = 4833344945293509188L;
// ------------------------------------------------------ Manifest Constants
/**
* The name of the context init parameter containing the name of the
* servlet context attribute under which our resulting {@link Catalog}
* will be stored.
*/
public static final String CONFIG_ATTR = ChainInit.CONFIG_ATTR;
/**
* The name of the context init parameter containing a comma-delimited
* list of class loader resources to be scanned.
*/
public static final String CONFIG_CLASS_RESOURCE =
ChainInit.CONFIG_CLASS_RESOURCE;
/**
* The name of the context init parameter containing a comma-delimited
* list of web application resources to be scanned.
*/
public static final String CONFIG_WEB_RESOURCE =
ChainInit.CONFIG_WEB_RESOURCE;
/**
* The name of the context init parameter containing the fully
* qualified class name of the {@code RuleSet} implementation
* for configuring our {@link ConfigParser}.
*/
public static final String RULE_SET = ChainInit.RULE_SET;
// ------------------------------------------------------------ Constructors
/**
* The Default-Constructor for this class.
*/
public ChainServlet() {
}
// --------------------------------------------------------- Servlet Methods
/**
* Clean up after ourselves as this application shuts down.
*/
@Override
public void destroy() {
final ServletConfig config = getServletConfig();
final ServletContext context = getServletContext();
ChainInit.destroy(context, config.getInitParameter(CONFIG_ATTR));
}
/**
* Create (if necessary) and configure a {@link Catalog} from the
* servlet init parameters that have been specified.
*
* @throws ServletException if the servlet could not be initialized
*/
@Override
public void init() throws ServletException {
final Logger logger = LoggerFactory.getLogger(ChainServlet.class);
final ServletConfig config = getServletConfig();
final ServletContext context = getServletContext();
logger.info("Initializing chain servlet '{}'", config.getServletName());
ChainInit.initialize(context, config.getInitParameter(CONFIG_ATTR), logger, false);
}
/**
* Does nothing; this servlet's only purpose is to initialize a Chain
* and store it in the servlet context.
*
* @param request the request issued by the client
* @param response the response to be returned to the cliengt
*
* @throws ServletException this exception is never thrown
* @throws IOException this exception is never thrown
*/
@Override
public void service(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException {
// do nothing
}
}