org.apache.commons.chain.CatalogFactory Maven / Gradle / Ivy
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/*
* 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;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import org.apache.commons.chain.impl.CatalogFactoryBase;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
/**
* A {@link CatalogFactory} is a class used to store and retrieve
* {@link Catalog}s. The factory allows for a default {@link Catalog}
* as well as {@link Catalog}s stored with a name key. Follows the
* Factory pattern (see GoF).
*
* The base CatalogFactory implementation also implements
* a resolution mechanism which allows lookup of a command based on a single
* String which encodes both the catalog and command names.
*
* @author Sean Schofield
* @version $Revision: 480477 $ $Date: 2006-11-29 08:34:52 +0000 (Wed, 29 Nov 2006) $
*/
public abstract class CatalogFactory {
/**
* Values passed to the getCommand(String) method should
* use this as the delimiter between the "catalog" name and the "command"
* name.
*/
public static final String DELIMITER = ":";
// --------------------------------------------------------- Public Methods
/**
* Gets the default instance of Catalog associated with the factory
* (if any); otherwise, return null.
*
* @return the default Catalog instance
*/
public abstract Catalog getCatalog();
/**
* Sets the default instance of Catalog associated with the factory.
*
* @param catalog the default Catalog instance
*/
public abstract void setCatalog(Catalog catalog);
/**
* Retrieves a Catalog instance by name (if any); otherwise
* return null.
*
* @param name the name of the Catalog to retrieve
* @return the specified Catalog
*/
public abstract Catalog getCatalog(String name);
/**
* Adds a named instance of Catalog to the factory (for subsequent
* retrieval later).
*
* @param name the name of the Catalog to add
* @param catalog the Catalog to add
*/
public abstract void addCatalog(String name, Catalog catalog);
/**
* Return an Iterator over the set of named
* {@link Catalog}s known to this {@link CatalogFactory}.
* If there are no known catalogs, an empty Iterator is returned.
* @return An Iterator of the names of the Catalogs known by this factory.
*/
public abstract Iterator getNames();
/**
* Return a Command based on the given commandID.
*
* At this time, the structure of commandID is relatively simple: if the
* commandID contains a DELIMITER, treat the segment of the commandID
* up to (but not including) the DELIMITER as the name of a catalog, and the
* segment following the DELIMITER as a command name within that catalog.
* If the commandID contains no DELIMITER, treat the commandID as the name
* of a command in the default catalog.
*
* To preserve the possibility of future extensions to this lookup
* mechanism, the DELIMITER string should be considered reserved, and
* should not be used in command names. commandID values which contain
* more than one DELIMITER will cause an
* IllegalArgumentException to be thrown.
*
* @param commandID the identifier of the command to return
* @return the command located with commandID, or null
* if either the command name or the catalog name cannot be resolved
* @throws IllegalArgumentException if the commandID contains more than
* one DELIMITER
*
* @since Chain 1.1
*/
public Command getCommand(String commandID) {
String commandName = commandID;
String catalogName = null;
Catalog catalog = null;
if (commandID != null) {
int splitPos = commandID.indexOf(DELIMITER);
if (splitPos != -1) {
catalogName = commandID.substring(0, splitPos);
commandName = commandID.substring(splitPos + DELIMITER.length());
if (commandName.indexOf(DELIMITER) != -1) {
throw new IllegalArgumentException("commandID [" +
commandID +
"] has too many delimiters (reserved for future use)");
}
}
}
if (catalogName != null) {
catalog = this.getCatalog(catalogName);
if (catalog == null) {
Log log = LogFactory.getLog(CatalogFactory.class);
log.warn("No catalog found for name: " + catalogName + ".");
return null;
}
} else {
catalog = this.getCatalog();
if (catalog == null) {
Log log = LogFactory.getLog(CatalogFactory.class);
log.warn("No default catalog found.");
return null;
}
}
return catalog.getCommand(commandName);
}
// ------------------------------------------------------- Static Variables
/**
* The set of registered {@link CatalogFactory} instances,
* keyed by the relevant class loader.
*/
private static Map factories = new HashMap();
// -------------------------------------------------------- Static Methods
/**
* Return the singleton {@link CatalogFactory} instance
* for the relevant ClassLoader. For applications
* that use a thread context class loader (such as web applications
* running inside a servet container), this will return a separate
* instance for each application, even if this class is loaded from
* a shared parent class loader.
*
* @return the per-application singleton instance of {@link CatalogFactory}
*/
public static CatalogFactory getInstance() {
CatalogFactory factory = null;
ClassLoader cl = getClassLoader();
synchronized (factories) {
factory = (CatalogFactory) factories.get(cl);
if (factory == null) {
factory = new CatalogFactoryBase();
factories.put(cl, factory);
}
}
return factory;
}
/**
* Clear all references to registered catalogs, as well as to the
* relevant class loader. This method should be called, for example,
* when a web application utilizing this class is removed from
* service, to allow for garbage collection.
*/
public static void clear() {
synchronized (factories) {
factories.remove(getClassLoader());
}
}
// ------------------------------------------------------- Private Methods
/**
* Return the relevant ClassLoader to use as a Map key
* for this request. If there is a thread context class loader, return
* that; otherwise, return the class loader that loaded this class.
*/
private static ClassLoader getClassLoader() {
ClassLoader cl = Thread.currentThread().getContextClassLoader();
if (cl == null) {
cl = CatalogFactory.class.getClassLoader();
}
return cl;
}
}