001: /* $Id: FinderFromClass.java 471661 2006-11-06 08:09:25Z skitching $
002: *
003: * Licensed to the Apache Software Foundation (ASF) under one or more
004: * contributor license agreements. See the NOTICE file distributed with
005: * this work for additional information regarding copyright ownership.
006: * The ASF licenses this file to You under the Apache License, Version 2.0
007: * (the "License"); you may not use this file except in compliance with
008: * the License. You may obtain a copy of the License at
009: *
010: * http://www.apache.org/licenses/LICENSE-2.0
011: *
012: * Unless required by applicable law or agreed to in writing, software
013: * distributed under the License is distributed on an "AS IS" BASIS,
014: * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015: * See the License for the specific language governing permissions and
016: * limitations under the License.
017: */
018:
019: package org.apache.commons.digester.plugins.strategies;
020:
021: import java.util.Properties;
022: import org.apache.commons.digester.Digester;
023: import org.apache.commons.digester.plugins.RuleFinder;
024: import org.apache.commons.digester.plugins.RuleLoader;
025: import org.apache.commons.digester.plugins.PluginException;
026:
027: /**
028: * A rule-finding algorithm which expects the caller to specify a classname and
029: * methodname as plugin properties.
030: *
031: * @since 1.6
032: */
033:
034: public class FinderFromClass extends RuleFinder {
035: public static String DFLT_RULECLASS_ATTR = "ruleclass";
036: public static String DFLT_METHOD_ATTR = "method";
037: public static String DFLT_METHOD_NAME = "addRules";
038:
039: private String ruleClassAttr;
040: private String methodAttr;
041: private String dfltMethodName;
042:
043: /**
044: * See {@link #findLoader}.
045: */
046: public FinderFromClass() {
047: this (DFLT_RULECLASS_ATTR, DFLT_METHOD_ATTR, DFLT_METHOD_NAME);
048: }
049:
050: /**
051: * Create a rule-finder which invokes a user-specified method on a
052: * user-specified class whenever dynamic rules for a plugin need to be
053: * loaded. See the findRules method for more info.
054: *
055: * @param ruleClassAttr must be non-null.
056: * @param methodAttr may be null.
057: * @param dfltMethodName may be null.
058: */
059: public FinderFromClass(String ruleClassAttr, String methodAttr,
060: String dfltMethodName) {
061: this .ruleClassAttr = ruleClassAttr;
062: this .methodAttr = methodAttr;
063: this .dfltMethodName = dfltMethodName;
064: }
065:
066: /**
067: * If there exists a property with the name matching constructor param
068: * ruleClassAttr, then load the specified class, locate the appropriate
069: * rules-adding method on that class, and return an object encapsulating
070: * that info.
071: * <p>
072: * If there is no matching property provided, then just return null.
073: * <p>
074: * The returned object (when non-null) will invoke the target method
075: * on the selected class whenever its addRules method is invoked. The
076: * target method is expected to have the following prototype:
077: * <code> public static void xxxxx(Digester d, String patternPrefix); </code>
078: * <p>
079: * The target method can be specified in several ways. If this object's
080: * constructor was passed a non-null methodAttr parameter, and the
081: * properties defines a value with that key, then that is taken as the
082: * target method name. If there is no matching property, or the constructor
083: * was passed null for methodAttr, then the dfltMethodName passed to the
084: * constructor is used as the name of the method on the target class. And
085: * if that was null, then DFLT_METHOD_NAME will be used.
086: * <p>
087: * When the user explicitly declares a plugin in the input xml, the
088: * xml attributes on the declaration tag are passed here as properties,
089: * so the user can select any class in the classpath (and any method on
090: * that class provided it has the correct prototype) as the source of
091: * dynamic rules for the plugged-in class.
092: */
093: public RuleLoader findLoader(Digester digester, Class pluginClass,
094: Properties p) throws PluginException {
095:
096: String ruleClassName = p.getProperty(ruleClassAttr);
097: if (ruleClassName == null) {
098: // nope, user hasn't requested dynamic rules to be loaded
099: // from a specific class.
100: return null;
101: }
102:
103: // ok, we are in business
104: String methodName = null;
105: if (methodAttr != null) {
106: methodName = p.getProperty(methodAttr);
107: }
108: if (methodName == null) {
109: methodName = dfltMethodName;
110: }
111: if (methodName == null) {
112: methodName = DFLT_METHOD_NAME;
113: }
114:
115: Class ruleClass;
116: try {
117: // load the plugin class object
118: ruleClass = digester.getClassLoader().loadClass(
119: ruleClassName);
120: } catch (ClassNotFoundException cnfe) {
121: throw new PluginException("Unable to load class "
122: + ruleClassName, cnfe);
123: }
124:
125: return new LoaderFromClass(ruleClass, methodName);
126: }
127: }
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