001// Copyright 2004, 2005 The Apache Software Foundation 002// 003// Licensed under the Apache License, Version 2.0 (the "License"); 004// you may not use this file except in compliance with the License. 005// You may obtain a copy of the License at 006// 007// http://www.apache.org/licenses/LICENSE-2.0 008// 009// Unless required by applicable law or agreed to in writing, software 010// distributed under the License is distributed on an "AS IS" BASIS, 011// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 012// See the License for the specific language governing permissions and 013// limitations under the License. 014 015package org.apache.tapestry.util; 016 017import java.util.HashMap; 018import java.util.Map; 019 020import org.apache.hivemind.util.Defense; 021 022/** 023 * Used to "uniquify" names within a given context. A base name is passed in, and the return value 024 * is the base name, or the base name extended with a suffix to make it unique. 025 * 026 * @author Howard Lewis Ship 027 * @since 3.0 028 */ 029 030public class IdAllocator 031{ 032 private static final String SEPARATOR = "_"; 033 034 private final Map _generatorMap = new HashMap(); 035 036 private final String _namespace; 037 038 private static class NameGenerator 039 { 040 private final String _baseId; 041 042 private int _index; 043 044 NameGenerator(String baseId) 045 { 046 _baseId = baseId + SEPARATOR; 047 } 048 049 public String nextId() 050 { 051 return _baseId + _index++; 052 } 053 } 054 055 public IdAllocator() 056 { 057 this(""); 058 } 059 060 public IdAllocator(String namespace) 061 { 062 Defense.notNull(namespace, "namespace"); 063 064 _namespace = namespace; 065 } 066 067 /** 068 * Allocates the id. Repeated calls for the same name will return "name", "name_0", "name_1", 069 * etc. 070 */ 071 072 public String allocateId(String name) 073 { 074 String key = name + _namespace; 075 076 NameGenerator g = (NameGenerator) _generatorMap.get(key); 077 String result = null; 078 079 if (g == null) 080 { 081 g = new NameGenerator(key); 082 result = key; 083 } 084 else 085 result = g.nextId(); 086 087 // Handle the degenerate case, where a base name of the form "foo$0" has been 088 // requested. Skip over any duplicates thus formed. 089 090 while (_generatorMap.containsKey(result)) 091 result = g.nextId(); 092 093 _generatorMap.put(result, g); 094 095 return result; 096 } 097 098 /** 099 * Clears the allocator, resetting it to freshly allocated state. 100 */ 101 102 public void clear() 103 { 104 _generatorMap.clear(); 105 } 106}