001    /* $Id: PluginAssertionFailure.java 476205 2006-11-17 16:43:10Z dennisl $
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;
020    
021    /**
022     * Thrown when a bug is detected in the plugins code.
023     * <p>
024     * This class is intended to be used in assertion statements, similar to
025     * the way that java 1.4's native assertion mechanism is used. However there
026     * is a difference: when a java 1.4 assertion fails, an AssertionError
027     * is thrown, which is a subclass of Error; here, the PluginAssertionFailure
028     * class extends RuntimeException rather than Error.
029     * <p>
030     * This difference in design is because throwing Error objects is not
031     * good in a container-based architecture.
032     * <p>
033     * Example:
034     * <pre>
035     *   if (impossibleCondition) {
036     *     throw new PluginAssertionFailure(
037     *       "internal error: impossible condition is true");
038     *   }
039     * </pre> 
040     * <p>
041     * Note that PluginAssertionFailure should <i>not</i> be thrown when user 
042     * input is bad, or when code external to the Digester module passes invalid 
043     * parameters to a plugins method. It should be used only in checks for 
044     * problems which indicate internal bugs within the plugins module.
045     *
046     * @since 1.6
047     */
048    public class PluginAssertionFailure extends RuntimeException {
049    
050        private Throwable cause = null;
051    
052        /**
053         * @param cause underlying exception that caused this to be thrown
054         */
055        public PluginAssertionFailure(Throwable cause) {
056            this(cause.getMessage());
057            this.cause = cause;
058        }
059    
060        /**
061         * @param msg describes the reason this exception is being thrown.
062         */
063        public PluginAssertionFailure(String msg) {
064            super(msg);
065        }
066    
067        /**
068         * @param msg describes the reason this exception is being thrown.
069         * @param cause underlying exception that caused this to be thrown
070         */
071        public PluginAssertionFailure(String msg, Throwable cause) {
072            this(msg);
073            this.cause = cause;
074        }
075        
076        /**
077         * Return the cause of this exception (if any) as specified in the
078         * exception constructor.
079         * 
080         * @since 1.8
081         */
082        public Throwable getCause() {
083            return cause;
084        }
085    }