package org.apache.commons.digester3.plugins.strategies;
/*
* 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.
*/
import java.util.Properties;
import org.apache.commons.digester3.Digester;
import org.apache.commons.digester3.plugins.PluginException;
import org.apache.commons.digester3.plugins.RuleFinder;
import org.apache.commons.digester3.plugins.RuleLoader;
/**
* A rule-finding algorithm which expects the caller to specify a classname and methodname as plugin properties.
*
* @since 1.6
*/
public class FinderFromClass
extends RuleFinder
{
private static final String DFLT_RULECLASS_ATTR = "ruleclass";
private static final String DFLT_METHOD_ATTR = "method";
private static final String DFLT_METHOD_NAME = "addRules";
private final String ruleClassAttr;
private final String methodAttr;
private final String dfltMethodName;
/**
* See {@link #findLoader}.
*/
public FinderFromClass()
{
this( DFLT_RULECLASS_ATTR, DFLT_METHOD_ATTR, DFLT_METHOD_NAME );
}
/**
* Create a rule-finder which invokes a user-specified method on a user-specified class whenever dynamic rules for a
* plugin need to be loaded. See the findRules method for more info.
*
* @param ruleClassAttr must be non-null.
* @param methodAttr may be null.
* @param dfltMethodName may be null.
*/
public FinderFromClass( String ruleClassAttr, String methodAttr, String dfltMethodName )
{
this.ruleClassAttr = ruleClassAttr;
this.methodAttr = methodAttr;
this.dfltMethodName = dfltMethodName;
}
/**
* If there exists a property with the name matching constructor param ruleClassAttr, then load the specified class,
* locate the appropriate rules-adding method on that class, and return an object encapsulating that info.
* <p>
* If there is no matching property provided, then just return null.
* <p>
* The returned object (when non-null) will invoke the target method on the selected class whenever its addRules
* method is invoked. The target method is expected to have the following prototype:
* <code> public static void xxxxx(Digester d, String patternPrefix); </code>
* <p>
* The target method can be specified in several ways. If this object's constructor was passed a non-null methodAttr
* parameter, and the properties defines a value with that key, then that is taken as the target method name. If
* there is no matching property, or the constructor was passed null for methodAttr, then the dfltMethodName passed
* to the constructor is used as the name of the method on the target class. And if that was null, then
* DFLT_METHOD_NAME will be used.
* <p>
* When the user explicitly declares a plugin in the input xml, the xml attributes on the declaration tag are passed
* here as properties, so the user can select any class in the classpath (and any method on that class provided it
* has the correct prototype) as the source of dynamic rules for the plugged-in class.
*
* @param digester The digester instance where locating plugin classes
* @param pluginClass The plugin Java class
* @param p The properties object that holds any xml attributes the user may have specified on the plugin
* declaration in order to indicate how to locate the plugin rules.
* @return a source of digester rules for the specified plugin class.
* @throws PluginException if the algorithm finds a source of rules, but there is something invalid
* about that source.
*/
@Override
public RuleLoader findLoader( Digester digester, Class<?> pluginClass, Properties p )
throws PluginException
{
String ruleClassName = p.getProperty( ruleClassAttr );
if ( ruleClassName == null )
{
// nope, user hasn't requested dynamic rules to be loaded
// from a specific class.
return null;
}
// ok, we are in business
String methodName = null;
if ( methodAttr != null )
{
methodName = p.getProperty( methodAttr );
}
if ( methodName == null )
{
methodName = dfltMethodName;
}
if ( methodName == null )
{
methodName = DFLT_METHOD_NAME;
}
Class<?> ruleClass;
try
{
// load the plugin class object
ruleClass = digester.getClassLoader().loadClass( ruleClassName );
}
catch ( ClassNotFoundException cnfe )
{
throw new PluginException( "Unable to load class " + ruleClassName, cnfe );
}
return new LoaderFromClass( ruleClass, methodName );
}
}