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Java > Open Source Codes > org > apache > tapestry > script > UniqueToken


1 // Copyright 2004, 2005 The Apache Software Foundation
2 //
3 // Licensed under the Apache License, Version 2.0 (the "License");
4 // you may not use this file except in compliance with the License.
5 // You may obtain a copy of the License at
6 //
7 // http://www.apache.org/licenses/LICENSE-2.0
8 //
9 // Unless required by applicable law or agreed to in writing, software
10 // distributed under the License is distributed on an "AS IS" BASIS,
11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12 // See the License for the specific language governing permissions and
13 // limitations under the License.
14
15 package org.apache.tapestry.script;
16
17 import org.apache.hivemind.Location;
18 import org.apache.tapestry.IRequestCycle;
19
20 /**
21  * Writes out its child tokens only the first time it executes
22  * (with a given tag). Uses
23  * {@link org.apache.tapestry.IRequestCycle#setAttribute(String, Object)}
24  * to identify whether a particular block has rendered yet.
25  *
26  * @author Howard Lewis Ship
27  * @since 3.0
28  */
29
30 class UniqueToken extends AbstractToken
31 {
32     public UniqueToken(Location location)
33     {
34         super(location);
35     }
36
37     public void write(StringBuffer JavaDoc buffer, ScriptSession session)
38     {
39         IRequestCycle cycle = session.getRequestCycle();
40
41         Location location = getLocation();
42         String JavaDoc tag = "<unique> " + location.toString();
43
44         if (cycle.getAttribute(tag) != null)
45             return;
46
47         cycle.setAttribute(tag, Boolean.TRUE);
48
49         writeChildren(buffer, session);
50     }
51
52 }
53
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