001 /* 002 * Licensed to the Apache Software Foundation (ASF) under one 003 * or more contributor license agreements. See the NOTICE file 004 * distributed with this work for additional information 005 * regarding copyright ownership. The ASF licenses this file 006 * to you under the Apache License, Version 2.0 (the 007 * "License"); you may not use this file except in compliance 008 * with 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, 013 * software distributed under the License is distributed on an 014 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY 015 * KIND, either express or implied. See the License for the 016 * specific language governing permissions and limitations 017 * under the License. 018 * 019 */ 020 package org.apache.directory.shared.asn1.codec.stateful; 021 022 023 import java.util.LinkedList; 024 025 026 /** 027 * A convenience callback which collects decoded or encoded objects to audit a 028 * codecs's activity. The callback also comes in handy when data is to be pushed 029 * through a codec and grabed immediately afterwords to serialize codec 030 * operation. 031 * 032 * @author <a href="mailto:dev@directory.apache.org"> Apache Directory Project</a> 033 * @version $Rev: 572195 $ 034 */ 035 public class CallbackHistory implements DecoderCallback, EncoderCallback 036 { 037 /** history of decoded objects in cronological order */ 038 private final LinkedList<Object> history; 039 040 /** the length of callback history stored */ 041 private final int length; 042 043 044 /** 045 * Creates an auditing callback that manages a history of indefinite length. 046 */ 047 public CallbackHistory() 048 { 049 this( -1 ); 050 } 051 052 053 /** 054 * Creates an auditing callback that manages a history of fixed or 055 * indefinite length. If the length is fixed the history effectively becomes 056 * a FIFO structure. 057 * 058 * @param length 059 * the maximum length of callback history to store before 060 * dropping decoded items, a length of zero or 1 corresponds to 061 * indefinite history 062 */ 063 public CallbackHistory(int length) 064 { 065 this.length = length; 066 history = new LinkedList<Object>(); 067 } 068 069 070 /* 071 * (non-Javadoc) 072 * 073 * @see org.apache.asn1.codec.stateful.DecoderCallback#decodeOccurred( 074 * org.apache.asn1.codec.stateful.StatefulDecoder, java.lang.Object) 075 */ 076 public void decodeOccurred( StatefulDecoder decoder, Object decoded ) 077 { 078 if ( length > 0 ) 079 { 080 while ( history.size() >= length ) 081 { 082 history.removeLast(); 083 } 084 } 085 086 history.addFirst( decoded ); 087 } 088 089 090 /** 091 * Callback to deliver a fully encoded object. 092 * 093 * @param encoder 094 * the stateful encoder driving the callback 095 * @param encoded 096 * the object that was encoded 097 */ 098 public void encodeOccurred( StatefulEncoder encoder, Object encoded ) 099 { 100 if ( length > 0 ) 101 { 102 while ( history.size() >= length ) 103 { 104 history.removeLast(); 105 } 106 } 107 108 history.addFirst( encoded ); 109 } 110 111 112 /** 113 * Gets the most recent decoded object if one exists. 114 * 115 * @return the most recent decoded object 116 * @throws java.util.NoSuchElementException 117 * if the history is empty 118 */ 119 public Object getMostRecent() 120 { 121 return history.getFirst(); 122 } 123 124 125 /** 126 * Gets the oldest decoded object if one exists. 127 * 128 * @return the oldest decoded object 129 * @throws java.util.NoSuchElementException 130 * if the history is empty 131 */ 132 public Object getOldest() 133 { 134 return history.getLast(); 135 } 136 137 138 /** 139 * Tests to see if the history is empty. 140 * 141 * @return true if the history is empty, false otherwise 142 */ 143 public boolean isEmpty() 144 { 145 return history.isEmpty(); 146 } 147 148 149 /** 150 * Clears the history of decoded items. 151 */ 152 public void clear() 153 { 154 history.clear(); 155 } 156 157 158 /** 159 * Gets the number of decoded items in the callback history. 160 * 161 * @return the number of decoded items in the callback history 162 */ 163 public int size() 164 { 165 return history.size(); 166 } 167 }