1 package org.apache.commons.digester3.examples.api.catalog; 2 3 /* 4 * Licensed to the Apache Software Foundation (ASF) under one or more 5 * contributor license agreements. See the NOTICE file distributed with 6 * this work for additional information regarding copyright ownership. 7 * The ASF licenses this file to You under the Apache License, Version 2.0 8 * (the "License"); you may not use this file except in compliance with 9 * the License. You may obtain a copy of the License at 10 * 11 * http://www.apache.org/licenses/LICENSE-2.0 12 * 13 * Unless required by applicable law or agreed to in writing, software 14 * distributed under the License is distributed on an "AS IS" BASIS, 15 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 16 * See the License for the specific language governing permissions and 17 * limitations under the License. 18 */ 19 20 import org.apache.commons.digester3.AbstractObjectCreationFactory; 21 import org.xml.sax.Attributes; 22 23 /** 24 * The Book class doesn't have a no-argument constructor, so the 25 * standard digester ObjectCreateRule can't be used to create instances 26 * of it. 27 * <p> 28 * To resolve this issue, the FactoryCreateRule can be used in 29 * conjunction with an appropriate factory class, like this one. 30 * The "createObject" method of the factory is invoked to generate 31 * object instances when required. 32 * <p> 33 * The factory object can access any xml attributes, plus of course 34 * any values set up within it before digester parsing starts (like 35 * JNDI references, database connections, etc) that it may in the 36 * process of generating an appropriate object. 37 * <p> 38 * Note that it is <i>not</i> possible for any data to be extracted 39 * from the body or subelements of the xml element that caused the 40 * createObject method on this factory to be invoked. For example: 41 * <pre> 42 * [book isdn="12345"] 43 * </pre> 44 * is fine; the isdn value can be accessed during the createObject method. 45 * However, given the xml: 46 * <pre> 47 * [book] 48 * [isdn]12345[/isdn] 49 * ... 50 * </pre> 51 * it is not possible to access the isdn number until after the 52 * Book instance has been created. 53 * <p> 54 * Note that even if the class to be created does have a default constructor, 55 * you may wish to use a factory class, in order to initialise the created 56 * object in specific ways, or insert created objects into a central 57 * register, etc. 58 * <p> 59 * And don't forget, either, that factories may be implemented as 60 * inner classes or anonymous classes if appropriate, reducing the 61 * overhead of using this functionality in many cases. 62 */ 63 public class BookFactory 64 extends AbstractObjectCreationFactory<Book> 65 { 66 67 @Override 68 public Book createObject( Attributes attributes ) 69 throws Exception 70 { 71 String isbn = attributes.getValue( "isbn" ); 72 73 if ( isbn == null ) 74 { 75 throw new Exception( "Mandatory isbn attribute not present on book tag." ); 76 } 77 78 return new Book( isbn ); 79 } 80 81 }