001 /*
002 $Id: RootLoader.java 3870 2006-06-28 12:59:18Z blackdrag $
003
004 Copyright 2003 (C) Jochen Theodorou. All Rights Reserved.
005
006 Redistribution and use of this software and associated documentation
007 ("Software"), with or without modification, are permitted provided
008 that the following conditions are met:
009
010 1. Redistributions of source code must retain copyright
011 statements and notices. Redistributions must also contain a
012 copy of this document.
013
014 2. Redistributions in binary form must reproduce the
015 above copyright notice, this list of conditions and the
016 following disclaimer in the documentation and/or other
017 materials provided with the distribution.
018
019 3. The name "groovy" must not be used to endorse or promote
020 products derived from this Software without prior written
021 permission of The Codehaus. For written permission,
022 please contact info@codehaus.org.
023
024 4. Products derived from this Software may not be called "groovy"
025 nor may "groovy" appear in their names without prior written
026 permission of The Codehaus. "groovy" is a registered
027 trademark of The Codehaus.
028
029 5. Due credit should be given to The Codehaus -
030 http://groovy.codehaus.org/
031
032 THIS SOFTWARE IS PROVIDED BY THE CODEHAUS AND CONTRIBUTORS
033 ``AS IS'' AND ANY EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT
034 NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
035 FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
036 THE CODEHAUS OR ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
037 INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
038 (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
039 SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
040 HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
041 STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
042 ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
043 OF THE POSSIBILITY OF SUCH DAMAGE.
044
045 */
046 package org.codehaus.groovy.tools;
047
048 import java.net.URL;
049 import java.net.URLClassLoader;
050
051 /**
052 * This ClassLoader should be used as root of class loaders. Any
053 * RootLoader does have it's own classpath. When searching for a
054 * class or resource this classpath will be used. Parent
055 * Classloaders are ignored first. If a class or resource
056 * can't be found in the classpath of the RootLoader, then parent is
057 * checked.
058 *
059 * <b>Note:</b> this is very against the normal behavior of
060 * classloaders. Normal is to frist check parent and then look in
061 * the ressources you gave this classloader.
062 *
063 * It's possible to add urls to the classpath at runtime through
064 * @see #addURL(URL)
065 *
066 * <b>Why using RootLoader?</b>
067 * If you have to load classes with multiple classloaders and a
068 * classloader does know a class which depends on a class only
069 * a child of this loader does know, then you won't be able to
070 * load the class. To load the class the child is not allowed
071 * to redirect it's search for the class to the parent first.
072 * That way the child can load the class. If the child does not
073 * have all classes to do this, this fails of course.
074 *
075 * For example:
076 *
077 * <pre>
078 * parentLoader (has classpath: a.jar;c.jar)
079 * |
080 * |
081 * childLoader (has classpath: a.jar;b.jar;c.jar)
082 * </pre>
083 *
084 * class C (from c.jar) extends B (from b.jar)
085 *
086 * childLoader.find("C")
087 * --> parentLoader does know C.class, try to load it
088 * --> to load C.class it has to load B.class
089 * --> parentLoader is unable to find B.class in a.jar or c.jar
090 * --> NoClassDefFoundException!
091 *
092 * if childLoader had tried to load the class by itself, there
093 * would be no problem. Changing childLoader to be a RootLoader
094 * instance will solve that problem.
095 *
096 * @author Jochen Theodorou
097 */
098 public class RootLoader extends URLClassLoader {
099
100 /**
101 * constructs a new RootLoader without classpath
102 * @param parent the parent Loader
103 */
104 private RootLoader(ClassLoader parent) {
105 this(new URL[0],parent);
106 }
107
108 /**
109 * constructs a new RootLoader with a parent loader and an
110 * array of URLs as classpath
111 */
112 public RootLoader(URL[] urls, ClassLoader parent) {
113 super(urls,parent);
114 }
115
116 private static ClassLoader chooseParent(){
117 ClassLoader cl = RootLoader.class.getClassLoader();
118 if (cl!=null) return cl;
119 return ClassLoader.getSystemClassLoader();
120 }
121
122 /**
123 * constructs a new RootLoader with a @see LoaderConfiguration
124 * object which holds the classpath
125 */
126 public RootLoader(LoaderConfiguration lc) {
127 this(chooseParent());
128 Thread.currentThread().setContextClassLoader(this);
129 URL[] urls = lc.getClassPathUrls();
130 for (int i=0; i<urls.length; i++) {
131 addURL(urls[i]);
132 }
133 }
134
135 /**
136 * loads a class using the name of the class
137 */
138 protected Class loadClass(final String name, boolean resolve) throws ClassNotFoundException {
139 Class c = this.findLoadedClass(name);
140 if (c!=null) return c;
141
142 try {
143 c = findClass(name);
144 } catch (ClassNotFoundException cnfe) {}
145 if (c==null) c= super.loadClass(name,resolve);
146
147 if (resolve) resolveClass(c);
148
149 return c;
150 }
151
152 /**
153 * returns the URL of a resource, or null if it is not found
154 */
155 public URL getResource(String name) {
156 URL url = findResource(name);
157 if (url==null) url=super.getResource(name);
158 return url;
159 }
160
161 /**
162 * adds an url to the classpath of this classloader
163 */
164 public void addURL(URL url) {
165 super.addURL(url);
166 }
167 }