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
019package 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 */
048public 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}