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| org.apache.commons.jelly.impl.DefaultTagLibraryResolver |
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| 1 | /* |
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| 2 | * Copyright 2002,2004 The Apache Software Foundation. |
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| 3 | * |
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| 4 | * Licensed under the Apache License, Version 2.0 (the "License"); |
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| 5 | * you may not use this file except in compliance with the License. |
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| 6 | * You may obtain a copy of the License at |
|
| 7 | * |
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| 8 | * http://www.apache.org/licenses/LICENSE-2.0 |
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| 9 | * |
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| 10 | * Unless required by applicable law or agreed to in writing, software |
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| 11 | * distributed under the License is distributed on an "AS IS" BASIS, |
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| 12 | * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
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| 13 | * See the License for the specific language governing permissions and |
|
| 14 | * limitations under the License. |
|
| 15 | */ |
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| 16 | package org.apache.commons.jelly.impl; |
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| 17 | ||
| 18 | import org.apache.commons.discovery.ResourceClass; |
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| 19 | import org.apache.commons.discovery.ResourceClassIterator; |
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| 20 | import org.apache.commons.discovery.resource.ClassLoaders; |
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| 21 | import org.apache.commons.discovery.resource.classes.DiscoverClasses; |
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| 22 | import org.apache.commons.jelly.TagLibrary; |
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| 23 | import org.apache.commons.jelly.util.ClassLoaderUtils; |
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| 24 | import org.apache.commons.logging.Log; |
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| 25 | import org.apache.commons.logging.LogFactory; |
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| 26 | ||
| 27 | ||
| 28 | /** |
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| 29 | * <p><code>DefaultTagLibraryResolver</code> is a default implemenation |
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| 30 | * which attempts to interpret the URI as a String called 'jelly:className' |
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| 31 | * and class load the given Java class. Otherwise META-INF/services/jelly/uri |
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| 32 | * is searched for on the thread context's class path and, if found, that |
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| 33 | * class will be loaded.</p> |
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| 34 | * |
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| 35 | * @author <a href="mailto:jstrachan@apache.org">James Strachan</a> |
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| 36 | * @version $Revision: 155420 $ |
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| 37 | */ |
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| 38 | public class DefaultTagLibraryResolver implements TagLibraryResolver { |
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| 39 | ||
| 40 | /** The Log to which logging calls will be made. */ |
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| 41 | 0 | private static final Log log = LogFactory.getLog(DefaultTagLibraryResolver.class); |
| 42 | ||
| 43 | private DiscoverClasses discovery; |
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| 44 | ||
| 45 | /** |
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| 46 | * The class loader to use for instantiating application objects. |
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| 47 | * If not specified, the context class loader, or the class loader |
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| 48 | * used to load this class itself, is used, based on the value of the |
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| 49 | * <code>useContextClassLoader</code> variable. |
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| 50 | */ |
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| 51 | private ClassLoader classLoader; |
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| 52 | ||
| 53 | /** |
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| 54 | * Do we want to use the Context ClassLoader when loading classes |
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| 55 | * for instantiating new objects? Default is <code>false</code>. |
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| 56 | */ |
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| 57 | 0 | private boolean useContextClassLoader = false; |
| 58 | ||
| 59 | ||
| 60 | 0 | public DefaultTagLibraryResolver() { |
| 61 | 0 | } |
| 62 | ||
| 63 | ||
| 64 | // TagLibraryResolver interface |
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| 65 | //------------------------------------------------------------------------- |
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| 66 | ||
| 67 | /** |
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| 68 | * Attempts to resolve the given URI to be associated with a TagLibrary |
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| 69 | * otherwise null is returned to indicate no tag library could be found |
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| 70 | * so that the namespace URI should be treated as just vanilla XML. |
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| 71 | */ |
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| 72 | public TagLibrary resolveTagLibrary(String uri) { |
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| 73 | 0 | DiscoverClasses discovery = getDiscoverClasses(); |
| 74 | 0 | String name = uri; |
| 75 | 0 | if ( uri.startsWith( "jelly:" ) ) { |
| 76 | 0 | name = "jelly." + uri.substring(6); |
| 77 | } |
|
| 78 | ||
| 79 | 0 | log.info( "Looking up service name: " + name ); |
| 80 | ||
| 81 | /* |
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| 82 | ClassLoaders loaders = ClassLoaders.getAppLoaders(TagLibrary.class, getClass(), false); |
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| 83 | ||
| 84 | DiscoverClass discover = new DiscoverClass(loaders); |
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| 85 | Class implClass = discover.find(TestInterface2.class); |
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| 86 | ||
| 87 | ||
| 88 | ||
| 89 | TagLibrary answer = null; |
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| 90 | try { |
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| 91 | answer = (TagLibrary) DiscoverSingleton.find(TagLibrary.class, name); |
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| 92 | } |
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| 93 | catch (Exception e) { |
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| 94 | log.error( "Could not load service: " + name ); |
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| 95 | } |
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| 96 | return answer; |
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| 97 | */ |
|
| 98 | 0 | ResourceClassIterator iter = discovery.findResourceClasses(name); |
| 99 | 0 | while (iter.hasNext()) { |
| 100 | 0 | ResourceClass resource = iter.nextResourceClass(); |
| 101 | try { |
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| 102 | 0 | Class typeClass = resource.loadClass(); |
| 103 | 0 | if ( typeClass != null ) { |
| 104 | 0 | return newInstance(uri, typeClass); |
| 105 | } |
|
| 106 | } |
|
| 107 | 0 | catch (Exception e) { |
| 108 | 0 | log.error( "Could not load service: " + resource ); |
| 109 | 0 | } |
| 110 | 0 | } |
| 111 | 0 | log.info( "Could not find any services for name: " + name ); |
| 112 | 0 | return null; |
| 113 | } |
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| 114 | ||
| 115 | // Properties |
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| 116 | //------------------------------------------------------------------------- |
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| 117 | ||
| 118 | /** |
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| 119 | * Return the class loader to be used for instantiating application objects |
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| 120 | * when required. This is determined based upon the following rules: |
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| 121 | * <ul> |
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| 122 | * <li>The class loader set by <code>setClassLoader()</code>, if any</li> |
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| 123 | * <li>The thread context class loader, if it exists and the |
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| 124 | * <code>useContextClassLoader</code> property is set to true</li> |
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| 125 | * <li>The class loader used to load the XMLParser class itself. |
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| 126 | * </ul> |
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| 127 | */ |
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| 128 | public ClassLoader getClassLoader() { |
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| 129 | 0 | return ClassLoaderUtils.getClassLoader(classLoader, useContextClassLoader, getClass()); |
| 130 | } |
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| 131 | ||
| 132 | /** |
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| 133 | * Set the class loader to be used for instantiating application objects |
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| 134 | * when required. |
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| 135 | * |
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| 136 | * @param classLoader The new class loader to use, or <code>null</code> |
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| 137 | * to revert to the standard rules |
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| 138 | */ |
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| 139 | public void setClassLoader(ClassLoader classLoader) { |
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| 140 | 0 | this.classLoader = classLoader; |
| 141 | 0 | } |
| 142 | ||
| 143 | /** |
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| 144 | * Return the boolean as to whether the context classloader should be used. |
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| 145 | */ |
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| 146 | public boolean getUseContextClassLoader() { |
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| 147 | 0 | return useContextClassLoader; |
| 148 | } |
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| 149 | ||
| 150 | /** |
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| 151 | * Determine whether to use the Context ClassLoader (the one found by |
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| 152 | * calling <code>Thread.currentThread().getContextClassLoader()</code>) |
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| 153 | * to resolve/load classes. If not |
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| 154 | * using Context ClassLoader, then the class-loading defaults to |
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| 155 | * using the calling-class' ClassLoader. |
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| 156 | * |
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| 157 | * @param boolean determines whether to use JellyContext ClassLoader. |
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| 158 | */ |
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| 159 | public void setUseContextClassLoader(boolean use) { |
|
| 160 | 0 | useContextClassLoader = use; |
| 161 | 0 | } |
| 162 | ||
| 163 | /** |
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| 164 | * @return the DiscoverClasses instance to use to locate services. |
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| 165 | * This object is lazily created if it has not been configured. |
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| 166 | */ |
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| 167 | public DiscoverClasses getDiscoverClasses() { |
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| 168 | 0 | if ( discovery == null ) { |
| 169 | 0 | ClassLoaders loaders = ClassLoaders.getAppLoaders(TagLibrary.class, getClass(), false); |
| 170 | 0 | discovery = new DiscoverClasses(loaders); |
| 171 | } |
|
| 172 | 0 | return discovery; |
| 173 | } |
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| 174 | ||
| 175 | /** |
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| 176 | * Sets the fully configured DiscoverClasses instance to be used to |
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| 177 | * lookup services |
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| 178 | */ |
|
| 179 | public void setDiscoverClasses(DiscoverClasses discovery) { |
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| 180 | 0 | this.discovery = discovery; |
| 181 | 0 | } |
| 182 | ||
| 183 | // Implementation methods |
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| 184 | //------------------------------------------------------------------------- |
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| 185 | ||
| 186 | /** |
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| 187 | * Instantiates the given class name. Otherwise an exception is logged |
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| 188 | * and null is returned |
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| 189 | */ |
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| 190 | protected TagLibrary loadClass(String uri, String className) { |
|
| 191 | try { |
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| 192 | 0 | Class theClass = getClassLoader().loadClass(className); |
| 193 | 0 | if ( theClass != null ) { |
| 194 | 0 | return newInstance(uri, theClass); |
| 195 | } |
|
| 196 | } |
|
| 197 | 0 | catch (ClassNotFoundException e) { |
| 198 | 0 | log.error("Could not find the class: " + className + " when trying to resolve URI: " + uri, e); |
| 199 | 0 | } |
| 200 | 0 | return null; |
| 201 | } |
|
| 202 | ||
| 203 | ||
| 204 | /** |
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| 205 | * Creates a new instance of the given TagLibrary class or |
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| 206 | * return null if it could not be instantiated. |
|
| 207 | */ |
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| 208 | protected TagLibrary newInstance(String uri, Class theClass) { |
|
| 209 | try { |
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| 210 | 0 | Object object = theClass.newInstance(); |
| 211 | 0 | if (object instanceof TagLibrary) { |
| 212 | 0 | return (TagLibrary) object; |
| 213 | } |
|
| 214 | else { |
|
| 215 | 0 | log.error( |
| 216 | "The tag library object mapped to: " |
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| 217 | + uri |
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| 218 | + " is not a TagLibrary. Object = " |
|
| 219 | + object); |
|
| 220 | } |
|
| 221 | } |
|
| 222 | 0 | catch (Exception e) { |
| 223 | 0 | log.error( |
| 224 | "Could not instantiate instance of class: " + theClass.getName() + ". Reason: " + e, |
|
| 225 | e); |
|
| 226 | 0 | } |
| 227 | 0 | return null; |
| 228 | } |
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| 229 | ||
| 230 | } |
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