Java tutorial
/* * JBoss, Home of Professional Open Source * Copyright 2013, Red Hat, Inc. and individual contributors * by the @authors tag. See the copyright.txt in the distribution for a * full listing of individual contributors. * * This 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 2.1 of * the License, or (at your option) any later version. * * This software 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 this software; if not, write to the Free * Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA * 02110-1301 USA, or see the FSF site: http://www.fsf.org. */ package org.richfaces.services; import java.io.BufferedReader; import java.io.IOException; import java.io.InputStream; import java.io.InputStreamReader; import java.net.URL; import java.net.URLConnection; import java.util.ArrayList; import java.util.Collection; import java.util.Enumeration; import java.util.HashSet; import java.util.LinkedHashSet; import java.util.List; import java.util.NoSuchElementException; import java.util.Set; import java.util.regex.Pattern; import com.google.common.collect.Iterables; /** * <p class="changed_added_4_0"> * This class loads services from files placed to the META-INF/services in classpath. * </p> * * @author asmirnov@exadel.com * */ public final class ServiceLoader { private static final String META_INF_SERVICES = "META-INF/services/"; private static final Pattern LEGAL_JAVA_NAME = Pattern .compile("^(([A-Za-z0-9_])+[\\.\\$])+[A-Z]([A-Za-z0-9_]*)$"); private ServiceLoader() { } /** * <p class="changed_added_4_0"> * Load and instantiate all service implementations. * </p> * * @param <S> * @param serviceClass * @return * @throws ServiceException */ public static <S> Collection<S> loadServices(Class<S> serviceClass) throws ServiceException { Collection<Class<? extends S>> serviceClasses = loadServiceClasses(serviceClass); List<S> instances = new ArrayList<S>(); for (Class<? extends S> implementationClass : serviceClasses) { instances.add(createInstance(implementationClass)); } return instances; } public static <S> S loadService(Class<S> serviceClass, Class<? extends S> defaultImplementation) { Collection<Class<? extends S>> serviceClasses = loadServiceClasses(serviceClass); try { return createInstance(Iterables.getLast(serviceClasses)); } catch (NoSuchElementException e) { return createInstance(defaultImplementation); } } public static <S> S loadService(Class<S> serviceClass) { Collection<Class<? extends S>> serviceClasses = loadServiceClasses(serviceClass); try { return createInstance(Iterables.getLast(serviceClasses)); } catch (NoSuchElementException e) { return null; } } private static <S> S createInstance(Class<? extends S> implementationClass) { try { return implementationClass.newInstance(); } catch (InstantiationException e) { throw new ServiceException("Cannot instantiate service class, does it have default constructor ?", e); } catch (IllegalAccessException e) { throw new ServiceException("Cannot instantiate service class, illegal access", e); } } /** * <p class="changed_added_4_0"> * Load service implementation classes. * </p> * * @param <S> * @param serviceClass * @return * @throws ServiceException */ public static <S> Collection<Class<? extends S>> loadServiceClasses(Class<S> serviceClass) throws ServiceException { ClassLoader classLoader = getClassLoader(serviceClass); Set<String> names = new LinkedHashSet<String>(); Enumeration<URL> resources; try { resources = classLoader.getResources(META_INF_SERVICES + serviceClass.getName()); while (resources.hasMoreElements()) { names.addAll(parse(resources.nextElement())); } } catch (IOException e) { throw new ServiceException("Error load service descriptions", e); } Set<Class<? extends S>> instanceClasses = new LinkedHashSet<Class<? extends S>>(); for (String className : names) { instanceClasses.add(loadClass(serviceClass, classLoader, className)); } return instanceClasses; } static Collection<String> parse(URL url) throws ServiceException, IOException { InputStream inputStream = null; try { URLConnection connection = url.openConnection(); try { connection.setUseCaches(false); } catch (IllegalArgumentException e) { // Do nothing. } Set<String> names = new HashSet<String>(); inputStream = connection.getInputStream(); BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream, "utf-8")); String line; while (null != (line = reader.readLine())) { parseLine(line, names); } return names; } finally { if (null != inputStream) { inputStream.close(); } } } /** * <p class="changed_added_4_0"> * Parse a single line from service description. Skips empty lines and comments started with # * </p> * * @param line * @param names * @throws ServiceException */ static void parseLine(String line, Collection<String> names) throws ServiceException { String name; int commentIndex = line.indexOf('#'); if (commentIndex >= 0) { name = line.substring(0, commentIndex); } else { name = line; } name = name.trim(); if (name.length() > 0) { if (LEGAL_JAVA_NAME.matcher(name).matches()) { names.add(name); } else { throw new ServiceException("Invalid java class name [" + line + "]"); } } } /** * <p class="changed_added_4_0"> * Get class loader * </p> * * @param <S> * @param serviceClass * @return context class loader or loader with which service class has been loaded. */ private static <S> ClassLoader getClassLoader(Class<S> serviceClass) { ClassLoader classLoader = Thread.currentThread().getContextClassLoader(); if (null == classLoader) { classLoader = serviceClass.getClassLoader(); } return classLoader; } private static <S> Class<? extends S> loadClass(Class<S> serviceClass, ClassLoader classLoader, String className) throws ServiceException { try { Class<?> implementationClass = classLoader.loadClass(className); if (serviceClass.isAssignableFrom(implementationClass)) { return implementationClass.asSubclass(serviceClass); } else { throw new ServiceException( "Class " + className + " in not the instance of " + serviceClass.getName()); } } catch (ClassNotFoundException e) { throw new ServiceException("Class " + className + " not found", e); } } }