| /** |
| * |
| * Copyright 2005 the original author or authors. |
| * |
| * Licensed under the Apache License, Version 2.0 (the "License"); |
| * you may not use this file except in compliance with the License. |
| * You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| package org.gbean.kernel; |
| |
| import java.io.BufferedReader; |
| import java.io.IOException; |
| import java.io.InputStream; |
| import java.io.InputStreamReader; |
| |
| import edu.emory.mathcs.backport.java.util.concurrent.ConcurrentHashMap; |
| import org.gbean.kernel.standard.StandardKernelFactory; |
| |
| /** |
| * The Kernel factory is used to construct and locate Kernels. This class is loosly based on the SAXParserFactory and |
| * the JMX MBeanServerFactory. To constuct a kernel use the following: |
| * <p><blockquote><pre> |
| * Kernel kernel = KernelFactory.newInstance().createKernel(name); |
| * </pre></blockquote> |
| * |
| * @author Dain Sundstrom |
| * @version $Id$ |
| * @since 1.0 |
| */ |
| public abstract class KernelFactory { |
| /** |
| * The name of the system property and META-INF/services used to locate the kernel factory class. |
| */ |
| public static final String KERNEL_FACTORY_KEY = KernelFactory.class.getName(); |
| |
| private static final ConcurrentHashMap kernels = new ConcurrentHashMap(1); |
| |
| /** |
| * Gets the kernel registered under the specified name. If no kernel is registered with the specified name, null |
| * is returned. |
| * |
| * @param name the name of the kernel to return |
| * @return the kernel or null if no kernel is registered under the specified name |
| */ |
| public static Kernel getKernel(String name) { |
| return (Kernel) kernels.get(name); |
| } |
| |
| /** |
| * Creates a kernel with the specified name. This method will attempt to locate a KernelFactory implementation |
| * using the following procedure |
| * <ul> <li> |
| * The org.gbean.kernel.KernelFactory system property. |
| * </li> <li> |
| * Use the <a href="http://java.sun.com/j2se/1.3/docs/guide/jar/jar.html">Jar Service Specification</a> |
| * This method will attempt to get the factory name from the file |
| * META-INF/services/org.gbean.kernel.KernelFactory loaded using the thread context class loader. |
| * </li> |
| * <li> |
| * The StandardKernel implementation. |
| * </li> |
| * </ul> |
| * The factory class is loaded and constucted using the thread context class loader, if present, or the class |
| * loader of this class. |
| * |
| * @return the kernel factory implementation |
| * @throws KernelFactoryError if the specified kernel factory can not be created |
| */ |
| public static KernelFactory newInstance() throws KernelFactoryError { |
| ClassLoader classLoader = Thread.currentThread().getContextClassLoader(); |
| if (classLoader == null) { |
| classLoader = KernelFactory.class.getClassLoader(); |
| } |
| |
| // System property |
| try { |
| String kernelFactoryName = System.getProperty(KERNEL_FACTORY_KEY); |
| if (kernelFactoryName != null) { |
| return createKernelFactory(kernelFactoryName, classLoader); |
| } |
| } catch (SecurityException se) { |
| } |
| |
| // Jar Service Specification - http://java.sun.com/j2se/1.3/docs/guide/jar/jar.html |
| String serviceId = "META-INF/services/" + KERNEL_FACTORY_KEY; |
| InputStream inputStream = null; |
| try { |
| inputStream = classLoader.getResourceAsStream(serviceId); |
| if (inputStream != null) { |
| BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream, "UTF-8")); |
| String kernelFactoryName = reader.readLine(); |
| reader.close(); |
| |
| if (kernelFactoryName != null && kernelFactoryName.length() > 0) { |
| return createKernelFactory(kernelFactoryName, classLoader); |
| } |
| } |
| } catch (Exception ignored) { |
| } finally { |
| if (inputStream != null) { |
| try { |
| inputStream.close(); |
| } catch (IOException ignored) { |
| } |
| inputStream = null; |
| } |
| } |
| |
| // Default is the standard kernel |
| return new StandardKernelFactory(); |
| } |
| |
| private static KernelFactory createKernelFactory(String className, ClassLoader classLoader) throws KernelFactoryError { |
| try { |
| return (KernelFactory) classLoader.loadClass(className).newInstance(); |
| } catch (ClassCastException e) { |
| throw new KernelFactoryError("Kernel factory class does not implement KernelFactory: " + className); |
| } catch (ClassNotFoundException e) { |
| throw new KernelFactoryError("Kernel factory class not found: " + className); |
| } catch (Exception e) { |
| throw new KernelFactoryError("Unable to instantiate kernel factory class: " + className, e); |
| } |
| } |
| |
| /** |
| * Creates a new kernel instance and registers it with the static KernelFactory registry. This allows the kernel |
| * to be retrieved from the {@link KernelFactory#getKernel(String)} method. |
| * |
| * @param name the name of the kernel to create |
| * @return the new kernel |
| * @throws KernelAlreadyExistsException is a kernel already exists with the specified name |
| */ |
| public final Kernel createKernel(String name) throws KernelAlreadyExistsException { |
| // quick check to see if a kernel already registerd wit the name |
| if (kernels.containsKey(name)) { |
| throw new KernelAlreadyExistsException(name); |
| } |
| |
| // create the kernel -- this may be an unnecessary construction, but it shouldn't be a big deal |
| Kernel kernel = createKernelInternal(name); |
| |
| // register the kernel, checking if someone snuck in an registered a kernel while we were creating ours |
| if (kernels.putIfAbsent(name, kernel) != null) { |
| throw new KernelAlreadyExistsException(name); |
| } |
| |
| return kernel; |
| } |
| |
| /** |
| * Creates the actual kernel instance which will be registerd in the KernelFactory. |
| * |
| * @param name the kernel name |
| * @return a new kernel instance |
| */ |
| protected abstract Kernel createKernelInternal(String name); |
| } |