Java tutorial
/* * Sonar, open source software quality management tool. * Copyright (C) 2008-2011 SonarSource * mailto:contact AT sonarsource DOT com * * Sonar is free software; you can redistribute it and/or * modify it under the terms of the GNU Lesser General Public * License as published by the Free Software Foundation; either * version 3 of the License, or (at your option) any later version. * * Sonar is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU * Lesser General Public License for more details. * * You should have received a copy of the GNU Lesser General Public * License along with Sonar; if not, write to the Free Software * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02 */ package org.sonar.core.classloaders; import java.net.URL; import java.util.Arrays; import java.util.Collection; import java.util.List; import com.google.common.collect.Lists; import org.apache.commons.lang.StringUtils; import org.codehaus.plexus.classworlds.ClassWorld; import org.codehaus.plexus.classworlds.realm.ClassRealm; import org.codehaus.plexus.classworlds.realm.DuplicateRealmException; import org.codehaus.plexus.classworlds.realm.NoSuchRealmException; import org.sonar.api.utils.Logs; import org.sonar.api.utils.SonarException; /** * Encapsulates manipulations with ClassLoaders, such as creation and establishing dependencies. Current implementation based on * {@link ClassWorld}. * * <h3>IMPORTANT</h3> * <p> * If we have pluginA , then all classes and resources from package and subpackages of <b>org.sonar.plugins.pluginA.api</b> will be visible * for all other plugins even if they located in dependent library. * </p> * * <h4>Search order for {@link ClassRealm} :</h4> * <ul> * <li>parent class loader (passed via the constructor) if there is one</li> * <li>imports</li> * <li>realm's constituents</li> * <li>parent realm</li> * </ul> * * @since 2.4 */ public class ClassLoadersCollection { private static final String[] PREFIXES_TO_EXPORT = { "org.sonar.plugins.", "com.sonar.plugins.", "com.sonarsource.plugins." }; private ClassWorld world = new ClassWorld(); private ClassLoader baseClassLoader; public ClassLoadersCollection(ClassLoader baseClassLoader) { this.baseClassLoader = baseClassLoader; } /** * Generates URLClassLoader with specified delegation model. * * @param key plugin key * @param urls libraries * @param childFirst true, if child-first delegation model required instead of parent-first * @return created ClassLoader, but actually this method shouldn't return anything, because dependencies must be established - see * {@link #done()}. */ public ClassLoader createClassLoader(String key, Collection<URL> urls, boolean childFirst) { try { List<URL> resources = Lists.newArrayList(); List<URL> others = Lists.newArrayList(); for (URL url : urls) { if (isResource(url)) { resources.add(url); } else { others.add(url); } } ClassLoader parent; if (resources.isEmpty()) { parent = baseClassLoader; } else { parent = new ResourcesClassLoader(resources, baseClassLoader); } final ClassRealm realm; if (childFirst) { ClassRealm parentRealm = world.newRealm(key + "-parent", parent); realm = parentRealm.createChildRealm(key); } else { realm = world.newRealm(key, parent); } for (URL url : others) { realm.addURL(url); } return realm; } catch (DuplicateRealmException e) { throw new SonarException(e); } } public void extend(String baseKey, String key, Collection<URL> urls) { try { ClassRealm base = world.getRealm(baseKey); base.createChildRealm(key); // we create new realm to be able to return it by key without conversion to baseKey for (URL url : urls) { base.addURL(url); } } catch (NoSuchRealmException e) { throw new SonarException(e); } catch (DuplicateRealmException e) { throw new SonarException(e); } } /** * Establishes dependencies among ClassLoaders. */ public void done() { for (Object o : world.getRealms()) { ClassRealm realm = (ClassRealm) o; if (!StringUtils.endsWith(realm.getId(), "-parent")) { String[] packagesToExport = new String[PREFIXES_TO_EXPORT.length]; for (int i = 0; i < PREFIXES_TO_EXPORT.length; i++) { // important to have dot at the end of package name only for classworlds 1.1 packagesToExport[i] = PREFIXES_TO_EXPORT[i] + realm.getId() + ".api"; } export(realm, packagesToExport); } } } /** * Exports specified packages from given ClassRealm to all others. */ private void export(ClassRealm realm, String... packages) { Logs.INFO.debug("Exporting " + Arrays.toString(packages) + " from " + realm.getId()); for (Object o : world.getRealms()) { ClassRealm dep = (ClassRealm) o; if (!StringUtils.equals(dep.getId(), realm.getId())) { try { for (String packageName : packages) { dep.importFrom(realm.getId(), packageName); } } catch (NoSuchRealmException e) { // should never happen throw new SonarException(e); } } } } /** * Note that this method should be called only after creation of all ClassLoaders - see {@link #done()}. */ public ClassLoader get(String key) { try { return world.getRealm(key); } catch (NoSuchRealmException e) { return null; } } private boolean isResource(URL url) { String path = url.getPath(); return !StringUtils.endsWith(path, ".jar") && !StringUtils.endsWith(path, "/"); } }