001 /* 002 * Copyright (c) 2007-2014 Concurrent, Inc. All Rights Reserved. 003 * 004 * Project and contact information: http://www.cascading.org/ 005 * 006 * This file is part of the Cascading project. 007 * 008 * Licensed under the Apache License, Version 2.0 (the "License"); 009 * you may not use this file except in compliance with the License. 010 * You may obtain a copy of the License at 011 * 012 * http://www.apache.org/licenses/LICENSE-2.0 013 * 014 * Unless required by applicable law or agreed to in writing, software 015 * distributed under the License is distributed on an "AS IS" BASIS, 016 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 017 * See the License for the specific language governing permissions and 018 * limitations under the License. 019 */ 020 021 package cascading.provider; 022 023 import java.net.URL; 024 025 import org.slf4j.Logger; 026 import org.slf4j.LoggerFactory; 027 028 /** 029 * Class ProviderLoader is the base class for loading various "provider" types. 030 * <p/> 031 * This loader can optinally load a provider implementation within its own ClassLoader using the 032 * {@link ChildFirstURLClassLoader}. 033 * 034 * @see FactoryLoader 035 * @see ServiceLoader 036 */ 037 public class ProviderLoader<Provider> 038 { 039 private static final Logger LOG = LoggerFactory.getLogger( ServiceLoader.class ); 040 URL libraryURL; 041 String[] exclusions; 042 043 ClassLoader classLoader; 044 045 public ProviderLoader() 046 { 047 } 048 049 public ProviderLoader( String[] exclusions, URL libraryURL ) 050 { 051 this.exclusions = exclusions; 052 this.libraryURL = libraryURL; 053 } 054 055 public Provider createProvider( String className ) 056 { 057 // test for ant style token escapes 058 if( className == null || className.isEmpty() ) 059 return null; 060 061 if( className.startsWith( "@" ) && className.endsWith( "@" ) ) 062 { 063 LOG.warn( "invalid classname: {}", className ); 064 return null; 065 } 066 067 try 068 { 069 Class<Provider> type = (Class<Provider>) getClassLoader().loadClass( className ); 070 071 return type.newInstance(); 072 } 073 catch( ClassNotFoundException exception ) 074 { 075 LOG.error( "unable to find service class: {}, with exception: {}", className, exception ); 076 } 077 catch( IllegalAccessException exception ) 078 { 079 LOG.error( "unable to instantiate service class: {}, with exception: {}", className, exception ); 080 } 081 catch( InstantiationException exception ) 082 { 083 LOG.error( "unable to instantiate service class: {}, with exception: {}", className, exception ); 084 } 085 086 return null; 087 } 088 089 private synchronized ClassLoader getClassLoader() 090 { 091 if( classLoader != null ) 092 return classLoader; 093 094 if( libraryURL == null ) 095 { 096 classLoader = Thread.currentThread().getContextClassLoader(); 097 } 098 else 099 { 100 LOG.info( "loading services from library: {}", libraryURL ); 101 102 classLoader = new ChildFirstURLClassLoader( exclusions, libraryURL ); 103 } 104 105 return classLoader; 106 } 107 }