1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one
3 * or more contributor license agreements. See the NOTICE file
4 * distributed with this work for additional information
5 * regarding copyright ownership. The ASF licenses this file
6 * to you under the Apache License, Version 2.0 (the
7 * "License"); you may not use this file except in compliance
8 * with the License. You may obtain a copy of the License at
9 *
10 * http://www.apache.org/licenses/LICENSE-2.0
11 *
12 * Unless required by applicable law or agreed to in writing,
13 * software distributed under the License is distributed on an
14 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
15 * KIND, either express or implied. See the License for the
16 * specific language governing permissions and limitations
17 * under the License.
18 *
19 */
20 package org.apache.directory.api.ldap.model.filter;
21
22
23 import java.text.ParseException;
24 import java.util.Comparator;
25 import java.util.List;
26 import java.util.Set;
27 import java.util.TreeSet;
28
29 import org.apache.directory.api.ldap.model.schema.SchemaManager;
30
31
32 /**
33 * Visitor which traverses a filter tree while normalizing the branch node
34 * order. Filter expressions can change the order of expressions in branch nodes
35 * without effecting the logical meaning of the expression. This visitor orders
36 * the children of expression tree branch nodes consistantly. It is really
37 * useful for comparing expression trees which may be altered for performance or
38 * altered because of codec idiosyncracies: for example the SNACC4J codec uses a
39 * hashmap to store expressions in a sequence which rearranges the order of
40 * children based on object hashcodes. We need this visitor to remove such
41 * inconsitancies in order hence normalizing the branch node's child order.
42 *
43 * @author <a href="mailto:dev@directory.apache.org">Apache Directory Project</a>
44 */
45 public class BranchNormalizedVisitor implements FilterVisitor
46 {
47 public Object visit( ExprNode node )
48 {
49 if ( !( node instanceof BranchNode ) )
50 {
51 return null;
52 }
53
54 BranchNode branch = ( BranchNode ) node;
55
56 Comparator<ExprNode> nodeComparator = new NodeComparator();
57
58 Set<ExprNode> set = new TreeSet<ExprNode>( nodeComparator );
59
60 List<ExprNode> children = branch.getChildren();
61
62 for ( ExprNode child : branch.getChildren() )
63 {
64 if ( !child.isLeaf() )
65 {
66 ExprNode newChild = ( ExprNode ) visit( child );
67
68 if ( newChild != null )
69 {
70 set.add( newChild );
71 }
72 }
73 else
74 {
75 set.add( child );
76 }
77 }
78
79 children.clear();
80
81 children.addAll( set );
82
83 return branch;
84 }
85
86
87 public boolean canVisit( ExprNode node )
88 {
89 return node instanceof BranchNode;
90 }
91
92
93 public boolean isPrefix()
94 {
95 return false;
96 }
97
98
99 public List<ExprNode> getOrder( BranchNode node, List<ExprNode> children )
100 {
101 return children;
102 }
103
104
105 /**
106 * Normalizes a filter expression to a canonical representation while
107 * retaining logical meaning of the expression.
108 *
109 * @param filter the filter to normalize
110 * @return the normalized version of the filter
111 * @throws java.text.ParseException
112 * if the filter is malformed
113 */
114 public static String getNormalizedFilter( SchemaManager schemaManager, String filter ) throws ParseException
115 {
116 ExprNode originalNode = FilterParser.parse( schemaManager, filter );
117
118 return getNormalizedFilter( originalNode );
119 }
120
121
122 /**
123 * Normalizes a filter expression to a canonical representation while
124 * retaining logical meaning of the expression.
125 *
126 * @param filter
127 * the filter to normalize
128 * @return the normalized String version of the filter
129 */
130 public static String getNormalizedFilter( ExprNode filter )
131 {
132 BranchNormalizedVisitor visitor = new BranchNormalizedVisitor();
133
134 ExprNode result = ( ExprNode ) visitor.visit( filter );
135
136 return result.toString().trim();
137 }
138
139 static class NodeComparator implements Comparator<ExprNode>
140 {
141 public int compare( ExprNode o1, ExprNode o2 )
142 {
143 StringBuilder buf = new StringBuilder();
144
145 buf.setLength( 0 );
146
147 String s1 = null;
148
149 buf.append( o1.toString() );
150
151 s1 = buf.toString();
152
153 buf.setLength( 0 );
154
155 String s2 = null;
156
157 buf.append( o2.toString() );
158
159 s2 = buf.toString();
160
161 return s1.compareTo( s2 );
162 }
163 }
164 }