001 /** 002 * Licensed to the Apache Software Foundation (ASF) under one or more 003 * contributor license agreements. See the NOTICE file distributed with 004 * this work for additional information regarding copyright ownership. 005 * The ASF licenses this file to You under the Apache License, Version 2.0 006 * (the "License"); you may not use this file except in compliance with 007 * the License. You may obtain a copy of the License at 008 * 009 * http://www.apache.org/licenses/LICENSE-2.0 010 * 011 * Unless required by applicable law or agreed to in writing, software 012 * distributed under the License is distributed on an "AS IS" BASIS, 013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 014 * See the License for the specific language governing permissions and 015 * limitations under the License. 016 */ 017 package org.apache.camel.processor.exceptionpolicy; 018 019 import java.util.ArrayList; 020 import java.util.Collections; 021 import java.util.Iterator; 022 import java.util.List; 023 import java.util.Map; 024 import java.util.Set; 025 026 import org.apache.camel.Exchange; 027 import org.apache.camel.model.ExceptionType; 028 import org.apache.commons.logging.Log; 029 import org.apache.commons.logging.LogFactory; 030 031 /** 032 * The default strategy used in Camel to resolve the {@link org.apache.camel.model.ExceptionType} that should 033 * handle the thrown exception. 034 * <p/> 035 * <b>Selection strategy:</b> 036 * <br/>This strategy applies the following rules: 037 * <ul> 038 * <li>Will walk the exception hieracy from bottom upwards till the thrown exception, meaning that the most outer caused 039 * by is selected first, ending with the thrown exception itself</li> 040 * <li>The exception type must be configured with an Exception that is an instance of the thrown exception, this 041 * is tested using the {@link #filter(org.apache.camel.model.ExceptionType, Class, Throwable)} method. </li> 042 * <li>If the exception type has exactly the thrown exception then its selected as its an exact match</li> 043 * <li>Otherwise the type that has an exception that is the closests super of the thrown exception is selected 044 * (recurring up the exception hierarchy)</li> 045 * </ul> 046 * <p/> 047 * <b>Fine grained matching:</b> 048 * <br/> If the {@link ExceptionType} has a when defined with an expression the type is also matches against 049 * the current exchange using the {@link #matchesWhen(org.apache.camel.model.ExceptionType, org.apache.camel.Exchange)} 050 * method. This can be used to for more fine grained matching, so you can e.g. define multiple sets of 051 * exception types with the same exception class(es) but have a predicate attached to select which to select at runtime. 052 */ 053 public class DefaultExceptionPolicyStrategy implements ExceptionPolicyStrategy { 054 055 private static final transient Log LOG = LogFactory.getLog(DefaultExceptionPolicyStrategy.class); 056 057 public ExceptionType getExceptionPolicy(Map<ExceptionPolicyKey, ExceptionType> exceptionPolicices, Exchange exchange, 058 Throwable exception) { 059 060 // recursive up the tree using the iterator 061 Iterator<Throwable> it = createExceptionIterator(exception); 062 while (it.hasNext()) { 063 ExceptionType type = findMatchedExceptionPolicy(exceptionPolicices, exchange, it.next()); 064 if (type != null) { 065 return type; 066 } 067 } 068 069 // no type found 070 return null; 071 } 072 073 074 private ExceptionType findMatchedExceptionPolicy(Map<ExceptionPolicyKey, ExceptionType> exceptionPolicices, Exchange exchange, 075 Throwable exception) { 076 if (LOG.isDebugEnabled()) { 077 LOG.debug("Finding best suited exception policy for thrown exception " + exception.getClass().getName()); 078 } 079 080 // the goal is to find the exception with the same/closet inheritance level as the target exception being thrown 081 int targetLevel = getInheritanceLevel(exception.getClass()); 082 // candidate is the best candidate found so far to return 083 ExceptionType candidate = null; 084 // difference in inheritance level between the current candidate and the thrown exception (target level) 085 int candidateDiff = Integer.MAX_VALUE; 086 087 // loop through all the entries and find the best candidates to use 088 Set<Map.Entry<ExceptionPolicyKey, ExceptionType>> entries = exceptionPolicices.entrySet(); 089 for (Map.Entry<ExceptionPolicyKey, ExceptionType> entry : entries) { 090 Class clazz = entry.getKey().getExceptionClass(); 091 ExceptionType type = entry.getValue(); 092 093 if (filter(type, clazz, exception)) { 094 095 // must match 096 if (!matchesWhen(type, exchange)) { 097 if (LOG.isDebugEnabled()) { 098 LOG.debug("The type did not match when: " + type); 099 } 100 continue; 101 } 102 103 // exact match then break 104 if (clazz.equals(exception.getClass())) { 105 candidate = type; 106 break; 107 } 108 109 // not an exact match so find the best candidate 110 int level = getInheritanceLevel(clazz); 111 int diff = targetLevel - level; 112 113 if (diff < candidateDiff) { 114 // replace with a much better candidate 115 candidate = type; 116 candidateDiff = diff; 117 } 118 } 119 } 120 121 if (LOG.isDebugEnabled()) { 122 if (candidate != null) { 123 LOG.debug("Using " + candidate + " as the exception policy"); 124 } else { 125 LOG.debug("No candidate found to be used as exception policy"); 126 } 127 } 128 129 return candidate; 130 } 131 132 /** 133 * Strategy to filter the given type exception class with the thrown exception 134 * 135 * @param type the exception type 136 * @param exceptionClass the current exception class for testing 137 * @param exception the thrown exception 138 * @return <tt>true</tt> if the to current exception class is a candidate, <tt>false</tt> to skip it. 139 */ 140 protected boolean filter(ExceptionType type, Class exceptionClass, Throwable exception) { 141 // must be instance of check to ensure that the exceptionClass is one type of the thrown exception 142 return exceptionClass.isInstance(exception); 143 } 144 145 /** 146 * Strategy method for matching the exception type with the current exchange. 147 * <p/> 148 * This default implementation will match as: 149 * <ul> 150 * <li>Always true if no when predicate on the exception type 151 * <li>Otherwise the when predicate is matches against the current exchange 152 * </ul> 153 * 154 * @param type the exception type 155 * @param exchange the current {@link Exchange} 156 * @return <tt>true</tt> if matched, <tt>false</tt> otherwise. 157 */ 158 protected boolean matchesWhen(ExceptionType type, Exchange exchange) { 159 if (type.getOnWhen() == null || type.getOnWhen().getExpression() == null) { 160 // if no predicate then it's always a match 161 return true; 162 } 163 return type.getOnWhen().getExpression().matches(exchange); 164 } 165 166 /** 167 * Strategy method creating the iterator to walk the exception in the order Camel should use 168 * for find the {@link ExceptionType} should be used. 169 * <p/> 170 * The default iterator will walk from the bottom upwards 171 * (the last caused by going upwards to the exception) 172 * 173 * @param exception the exception 174 * @return the iterator 175 */ 176 protected Iterator<Throwable> createExceptionIterator(Throwable exception) { 177 return new ExceptionIterator(exception); 178 } 179 180 private static int getInheritanceLevel(Class clazz) { 181 if (clazz == null || "java.lang.Object".equals(clazz.getName())) { 182 return 0; 183 } 184 return 1 + getInheritanceLevel(clazz.getSuperclass()); 185 } 186 187 private class ExceptionIterator implements Iterator<Throwable> { 188 private List<Throwable> tree = new ArrayList<Throwable>(); 189 private Iterator<Throwable> it; 190 191 public ExceptionIterator(Throwable exception) { 192 Throwable current = exception; 193 // spool to the bottom of the caused by tree 194 while (current != null) { 195 tree.add(current); 196 current = current.getCause(); 197 } 198 199 // reverse tree so we go from bottom to top 200 Collections.reverse(tree); 201 it = tree.iterator(); 202 } 203 204 public boolean hasNext() { 205 return it.hasNext(); 206 } 207 208 public Throwable next() { 209 return it.next(); 210 } 211 212 public void remove() { 213 it.remove(); 214 } 215 } 216 217 }