001 /* 002 * Licensed to the Apache Software Foundation (ASF) under one or more 003 * contributor license agreements. See the NOTICE file distributed with 004 * this work for additional information regarding copyright ownership. 005 * The ASF licenses this file to You under the Apache License, Version 2.0 006 * (the "License"); you may not use this file except in compliance with 007 * the License. You may obtain a copy of the License at 008 * 009 * http://www.apache.org/licenses/LICENSE-2.0 010 * 011 * Unless required by applicable law or agreed to in writing, software 012 * distributed under the License is distributed on an "AS IS" BASIS, 013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 014 * See the License for the specific language governing permissions and 015 * limitations under the License. 016 */ 017 package org.apache.commons.discovery.tools; 018 019 import org.apache.commons.discovery.ResourceClass; 020 import org.apache.commons.discovery.ResourceClassIterator; 021 import org.apache.commons.discovery.resource.classes.DiscoverClasses; 022 import org.apache.commons.discovery.resource.ClassLoaders; 023 024 025 /** 026 * Holder for a default class. 027 * 028 * Class may be specified by name (String) or class (Class). 029 * Using the holder complicates the users job, but minimized # of API's. 030 * 031 * @author Richard A. Sitze 032 */ 033 public class DefaultClassHolder { 034 private Class defaultClass; 035 private final String defaultName; 036 037 public DefaultClassHolder(Class defaultClass) { 038 this.defaultClass = defaultClass; 039 this.defaultName = defaultClass.getName(); 040 } 041 042 public DefaultClassHolder(String defaultName) { 043 this.defaultClass = null; 044 this.defaultName = defaultName; 045 } 046 047 /** 048 * @param spi non-null SPI 049 * @param loaders Used only if class needs to be loaded. 050 * 051 * @return Default Class. Load the class if necessary, 052 * and verify that it implements the SPI. 053 * (this forces the check, no way out..). 054 */ 055 public Class getDefaultClass(SPInterface spi, ClassLoaders loaders) { 056 if (defaultClass == null) { 057 DiscoverClasses classDiscovery = new DiscoverClasses(loaders); 058 ResourceClassIterator classes = classDiscovery.findResourceClasses(getDefaultName()); 059 if (classes.hasNext()) { 060 ResourceClass info = classes.nextResourceClass(); 061 try { 062 defaultClass = info.loadClass(); 063 } catch (Exception e) { 064 // ignore 065 } 066 } 067 } 068 069 if (defaultClass != null) { 070 spi.verifyAncestory(defaultClass); 071 } 072 073 return defaultClass; 074 } 075 076 public String getDefaultName() { 077 return defaultName; 078 } 079 }