KickJava   Java API By Example, From Geeks To Geeks.

Java > Open Source Codes > org > apache > ldap > server > db > IndexAssertionEnumeration


1 /*
2  * Copyright 2004 The Apache Software Foundation
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  * http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  *
16  */
17 package org.apache.ldap.server.db;
18
19
20 import javax.naming.NamingEnumeration JavaDoc;
21 import javax.naming.NamingException JavaDoc;
22 import java.util.HashMap JavaDoc;
23 import java.util.Map JavaDoc;
24 import java.util.NoSuchElementException JavaDoc;
25
26
27 /**
28  * A prefetching NamingEnumeration over an underlying NamingEnumeration which
29  * determines if a element should be returned based on a Assertion.
30  *
31  * @author <a HREF="mailto:dev@directory.apache.org">Apache Directory Project</a>
32  * @version $Rev: 169198 $
33  */
34 public class IndexAssertionEnumeration
35     implements NamingEnumeration JavaDoc
36 {
37     /** The prefetched candidate */
38     private final IndexRecord prefetched = new IndexRecord();
39     /** The returned candidate */
40     private final IndexRecord candidate = new IndexRecord();
41     /** The iteration cursor */
42     private final NamingEnumeration JavaDoc underlying;
43     /** LUT used to avoid returning duplicates */
44     private final Map JavaDoc candidates;
45     /** */
46     private final IndexAssertion assertion;
47     /** */
48     private final boolean checkDups;
49     /** */
50     private boolean hasMore = true;
51
52
53     // ------------------------------------------------------------------------
54 // C O N S T R U C T O R S
55 // ------------------------------------------------------------------------
56
57
58     /**
59      * TODO Domument me!
60      *
61      * @param underlying TODO
62      * @param assertion TODO
63      * @throws NamingException TODO
64      */
65     public IndexAssertionEnumeration( NamingEnumeration JavaDoc underlying,
66         IndexAssertion assertion ) throws NamingException JavaDoc
67     {
68         this.underlying = underlying;
69         candidates = null;
70         this.assertion = assertion;
71         checkDups = false;
72         prefetch();
73     }
74
75
76     /**
77      * TODO Domument me!
78      *
79      * @param underlying TODO
80      * @param assertion TODO
81      * @param enableDupCheck TODO
82      * @throws NamingException TODO
83      */
84     public IndexAssertionEnumeration( NamingEnumeration JavaDoc underlying,
85         IndexAssertion assertion, boolean enableDupCheck )
86         throws NamingException JavaDoc
87     {
88         this.underlying = underlying;
89         candidates = new HashMap JavaDoc();
90         this.assertion = assertion;
91         checkDups = enableDupCheck;
92         prefetch();
93     }
94
95
96     // ------------------------------------------------------------------------
97 // Enumeration Method Implementations
98 // ------------------------------------------------------------------------
99
100
101     /**
102      * @see java.util.Enumeration#nextElement()
103      */
104     public Object JavaDoc nextElement()
105     {
106         try
107         {
108             return next();
109         }
110         catch ( NamingException JavaDoc e )
111         {
112             throw new NoSuchElementException JavaDoc();
113         }
114     }
115     
116     
117     /**
118      * @see java.util.Enumeration#hasMoreElements()
119      */
120     public boolean hasMoreElements()
121     {
122         return hasMore;
123     }
124     
125     
126     // ------------------------------------------------------------------------
127 // NamingEnumeration Method Implementations
128 // ------------------------------------------------------------------------
129
130
131     /**
132      * @see javax.naming.NamingEnumeration#next()
133      */
134     public Object JavaDoc next() throws NamingException JavaDoc
135     {
136         candidate.copy( prefetched );
137         prefetch();
138         return candidate;
139     }
140
141     
142     /**
143      * @see javax.naming.NamingEnumeration#hasMore()
144      */
145     public boolean hasMore()
146     {
147         return hasMore;
148     }
149
150     
151     /**
152      * @see javax.naming.NamingEnumeration#close()
153      */
154     public void close() throws NamingException JavaDoc
155     {
156         hasMore = false;
157         underlying.close();
158     }
159
160
161     // ------------------------------------------------------------------------
162 // Private and Protected Methods
163 // ------------------------------------------------------------------------
164
165
166     /**
167      * TODO Document me!
168      *
169      * @throws NamingException TODO
170      */
171     private void prefetch() throws NamingException JavaDoc
172     {
173         IndexRecord rec = null;
174
175         /*
176          * Scan underlying Cursor until we arrive at the next valid candidate
177          * if the cursor is exhuasted we clean up after completing the loop
178          */
179         while ( underlying.hasMore() )
180         {
181             rec = ( IndexRecord ) underlying.next();
182
183             // If value is valid then we set it as the next candidate to return
184 if ( assertion.assertCandidate( rec ) )
185             {
186                 if ( checkDups )
187                 {
188                     boolean dup = candidates.containsKey( rec.getEntryId() );
189                     
190                     if ( dup )
191                     {
192                         /*
193                          * Dup checking is on and candidate is a duplicate that
194                          * has already been seen so we need to skip it.
195                          */
196                         continue;
197                     }
198                     else
199                     {
200                         /*
201                          * Dup checking is on and the candidate is not in the
202                          * dup LUT so we need to set it as the next to return
203                          * and add it to the LUT in case we encounter it another
204                          * time.
205                          */
206                         prefetched.copy( rec );
207                         candidates.put( rec.getEntryId(), rec.getEntryId() );
208                         return;
209                     }
210                 }
211
212                 prefetched.copy( rec );
213                 return;
214             }
215         }
216
217         // At this pt the underlying Cursor has been exhausted so we close up
218 close();
219     }
220 }
221
Popular Tags