| package org.apache.commons.digester3.examples.api.catalog; |
| |
| /* |
| * Licensed to the Apache Software Foundation (ASF) under one or more |
| * contributor license agreements. See the NOTICE file distributed with |
| * this work for additional information regarding copyright ownership. |
| * The ASF licenses this file to You 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. |
| */ |
| |
| import org.apache.commons.digester3.AbstractObjectCreationFactory; |
| import org.xml.sax.Attributes; |
| |
| /** |
| * The Book class doesn't have a no-argument constructor, so the |
| * standard digester ObjectCreateRule can't be used to create instances |
| * of it. |
| * <p> |
| * To resolve this issue, the FactoryCreateRule can be used in |
| * conjunction with an appropriate factory class, like this one. |
| * The "createObject" method of the factory is invoked to generate |
| * object instances when required. |
| * <p> |
| * The factory object can access any xml attributes, plus of course |
| * any values set up within it before digester parsing starts (like |
| * JNDI references, database connections, etc) that it may in the |
| * process of generating an appropriate object. |
| * <p> |
| * Note that it is <i>not</i> possible for any data to be extracted |
| * from the body or subelements of the xml element that caused the |
| * createObject method on this factory to be invoked. For example: |
| * <pre> |
| * [book isdn="12345"] |
| * </pre> |
| * is fine; the isdn value can be accessed during the createObject method. |
| * However, given the xml: |
| * <pre> |
| * [book] |
| * [isdn]12345[/isdn] |
| * ... |
| * </pre> |
| * it is not possible to access the isdn number until after the |
| * Book instance has been created. |
| * <p> |
| * Note that even if the class to be created does have a default constructor, |
| * you may wish to use a factory class, in order to initialise the created |
| * object in specific ways, or insert created objects into a central |
| * register, etc. |
| * <p> |
| * And don't forget, either, that factories may be implemented as |
| * inner classes or anonymous classes if appropriate, reducing the |
| * overhead of using this functionality in many cases. |
| */ |
| public class BookFactory |
| extends AbstractObjectCreationFactory<Book> |
| { |
| |
| @Override |
| public Book createObject( Attributes attributes ) |
| throws Exception |
| { |
| String isbn = attributes.getValue( "isbn" ); |
| |
| if ( isbn == null ) |
| { |
| throw new Exception( "Mandatory isbn attribute not present on book tag." ); |
| } |
| |
| return new Book( isbn ); |
| } |
| |
| } |