1 /* ServiceProviderLoadingAction.java -- Action for loading plug-in services. 2 Copyright (C) 2004 Free Software Foundation 3 4 This file is part of GNU Classpath. 5 6 GNU Classpath is free software; you can redistribute it and/or modify 7 it under the terms of the GNU General Public License as published by 8 the Free Software Foundation; either version 2, or (at your option) 9 any later version. 10 11 GNU Classpath is distributed in the hope that it will be useful, but 12 WITHOUT ANY WARRANTY; without even the implied warranty of 13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 14 General Public License for more details. 15 16 You should have received a copy of the GNU General Public License 17 along with GNU Classpath; see the file COPYING. If not, write to the 18 Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 19 02110-1301 USA. 20 21 Linking this library statically or dynamically with other modules is 22 making a combined work based on this library. Thus, the terms and 23 conditions of the GNU General Public License cover the whole 24 combination. 25 26 As a special exception, the copyright holders of this library give you 27 permission to link this library with independent modules to produce an 28 executable, regardless of the license terms of these independent 29 modules, and to copy and distribute the resulting executable under 30 terms of your choice, provided that you also meet, for each linked 31 independent module, the terms and conditions of the license of that 32 module. An independent module is a module which is not derived from 33 or based on this library. If you modify this library, you may extend 34 this exception to your version of the library, but you are not 35 obligated to do so. If you do not wish to do so, delete this 36 exception statement from your version. */ 37 38 39 package gnu.classpath; 40 41 import java.security.PrivilegedExceptionAction; 42 43 /** 44 * A privileged action for creating a new instance of a service 45 * provider. 46 * 47 * <p>Class loading and instantiation is encapsulated in a 48 * <code>PriviledgedAction</code> in order to restrict the loaded 49 * service providers to the {@link java.security.AccessControlContext} 50 * that was active when {@link 51 * gnu.classpath.ServiceFactory#lookupProviders(Class, ClassLoader)} was 52 * called, even though the actual loading is delayed to the time when the 53 * provider is actually needed. 54 * 55 * @author <a href="mailto:brawer@dandelis.ch">Sascha Brawer</a> 56 */ 57 final class ServiceProviderLoadingAction<P> 58 implements PrivilegedExceptionAction<P> 59 { 60 /** 61 * The interface to which the loaded service provider implementation 62 * must conform. Usually, this is a Java interface type, but it 63 * might also be an abstract class or even a concrete class. 64 */ 65 private final Class<P> spi; 66 67 68 /** 69 * The fully qualified name of the class that gets loaded when 70 * this action is executed. 71 */ 72 private final String providerName; 73 74 75 /** 76 * The ClassLoader that gets used for loading the service provider 77 * class. 78 */ 79 private final ClassLoader loader; 80 81 82 /** 83 * Constructs a privileged action for loading a service provider. 84 * 85 * @param spi the interface to which the loaded service provider 86 * implementation must conform. Usually, this is a Java interface 87 * type, but it might also be an abstract class or even a concrete 88 * superclass. 89 * 90 * @param providerName the fully qualified name of the class that 91 * gets loaded when this action is executed. 92 * 93 * @param loader the ClassLoader that gets used for loading the 94 * service provider class. 95 * 96 * @throws IllegalArgumentException if <code>spi</code>, 97 * <code>providerName</code> or <code>loader</code> is 98 * <code>null</code>. 99 */ ServiceProviderLoadingAction(Class<P> spi, String providerName, ClassLoader loader)100 ServiceProviderLoadingAction(Class<P> spi, String providerName, 101 ClassLoader loader) 102 { 103 if (spi == null || providerName == null || loader == null) 104 throw new IllegalArgumentException(); 105 106 this.spi = spi; 107 this.providerName = providerName; 108 this.loader = loader; 109 } 110 111 112 /** 113 * Loads an implementation class for a service provider, and creates 114 * a new instance of the loaded class by invoking its public 115 * no-argument constructor. 116 * 117 * @return a new instance of the class whose name was passed as 118 * <code>providerName</code> to the constructor. 119 * 120 * @throws ClassCastException if the service provider does not 121 * implement the <code>spi</code> interface that was passed to the 122 * constructor. 123 * 124 * @throws IllegalAccessException if the service provider class or 125 * its no-argument constructor are not <code>public</code>. 126 * 127 * @throws InstantiationException if the service provider class is 128 * <code>abstract</code>, an interface, a primitive type, an array 129 * class, or void; or if service provider class does not have a 130 * no-argument constructor; or if there some other problem with 131 * creating a new instance of the service provider. 132 */ run()133 public P run() 134 throws Exception 135 { 136 Class<P> loadedClass; 137 P serviceProvider; 138 139 loadedClass = (Class<P>) loader.loadClass(providerName); 140 serviceProvider = loadedClass.newInstance(); 141 142 // Ensure that the loaded provider is actually implementing 143 // the service provider interface. 144 if (!spi.isInstance(serviceProvider)) 145 throw new ClassCastException(spi.getName()); 146 147 return serviceProvider; 148 } 149 } 150