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Java > Open Source Codes > org > apache > commons > jelly > tags > define > ClassLoaderTag


1 /*
2  * Copyright 2002,2004 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.commons.jelly.tags.define;
18
19 import java.net.MalformedURLException JavaDoc;
20 import java.net.URL JavaDoc;
21 import java.net.URLClassLoader JavaDoc;
22
23 import org.apache.commons.jelly.JellyTagException;
24 import org.apache.commons.jelly.MissingAttributeException;
25 import org.apache.commons.jelly.XMLOutput;
26 import org.apache.commons.jelly.util.ClassLoaderUtils;
27 import org.apache.commons.logging.Log;
28 import org.apache.commons.logging.LogFactory;
29
30
31 /**
32  * Creates a new <code>URLClassLoader</code> to dynamically
33  * load tags froms.
34  *
35  * @author <a HREF="mailto:stephenh@chase3000.com">Stephen Haberman</a>
36  * @version $Revision: 155420 $
37  */

38 public class ClassLoaderTag extends BeanTag {
39
40     /** The Log to which logging calls will be made. */
41     private static final Log log = LogFactory.getLog(ClassLoaderTag.class);
42
43     /** The name to export the classloader to. */
44     private String JavaDoc var;
45
46     /** The URL to load the classes from. */
47     private String JavaDoc url;
48
49     // Properties
50
//-------------------------------------------------------------------------
51

52     /**
53      * @return the variable to store the class loader in
54      */

55     public String JavaDoc getVar() {
56         return this.var;
57     }
58
59     /**
60      * @param var the variable to store the class loader in
61      */

62     public void setVar(String JavaDoc var) {
63         this.var = var;
64     }
65
66     /**
67      * @return the url to load the classes from
68      */

69     public String JavaDoc getUrl() {
70         return this.url;
71     }
72
73     /**
74      * @param url the url to load the classes from
75      */

76     public void setUrl(String JavaDoc url) {
77         this.url = url;
78     }
79
80     // Implementation methods
81
//-------------------------------------------------------------------------
82

83     public void doTag(XMLOutput output) throws MissingAttributeException, JellyTagException {
84         if ( getVar() == null ) {
85             throw new MissingAttributeException( "var" );
86         }
87         if ( getUrl() == null ) {
88             throw new MissingAttributeException( "url" );
89         }
90
91         ClassLoader JavaDoc parent = Thread.currentThread().getContextClassLoader();
92         if (parent == null) {
93             parent = ClassLoaderUtils.getClassLoader(getClass());
94         }
95
96         URLClassLoader JavaDoc newClassLoader = null;
97
98         try {
99             newClassLoader =
100               new URLClassLoader JavaDoc( new URL JavaDoc[] { new URL JavaDoc(getUrl()) }, parent );
101         } catch (MalformedURLException JavaDoc e) {
102             throw new JellyTagException(e);
103         }
104
105         log.debug("Storing the new classloader in " + getVar());
106
107         context.setVariable(getVar(), newClassLoader);
108     }
109
110 }
111
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