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From rdon...@apache.org
Subject cvs commit: jakarta-commons/betwixt/src/java/org/apache/commons/betwixt/io/read ChainedBeanCreatorFactory.java
Date Thu, 21 Aug 2003 22:39:00 GMT
rdonkin     2003/08/21 15:39:00

  Added:       betwixt/src/java/org/apache/commons/betwixt/io/read
                        ChainedBeanCreatorFactory.java
  Log:
  Reafactored read bean creation into chain of independet creators. It can now be extended
by users.
  
  Revision  Changes    Path
  1.1                  jakarta-commons/betwixt/src/java/org/apache/commons/betwixt/io/read/ChainedBeanCreatorFactory.java
  
  Index: ChainedBeanCreatorFactory.java
  ===================================================================
  /*
   * $Header: /home/cvs/jakarta-commons/betwixt/src/java/org/apache/commons/betwixt/io/read/ChainedBeanCreatorFactory.java,v
1.1 2003/08/21 22:39:00 rdonkin Exp $
   * $Revision: 1.1 $
   * $Date: 2003/08/21 22:39:00 $
   *
   * ====================================================================
   *
   * The Apache Software License, Version 1.1
   *
   * Copyright (c) 1999-2002 The Apache Software Foundation.  All rights
   * reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   *
   * 1. Redistributions of source code must retain the above copyright
   *    notice, this list of conditions and the following disclaimer.
   *
   * 2. Redistributions in binary form must reproduce the above copyright
   *    notice, this list of conditions and the following disclaimer in
   *    the documentation and/or other materials provided with the
   *    distribution.
   *
   * 3. The end-user documentation included with the redistribution, if
   *    any, must include the following acknowlegement:
   *       "This product includes software developed by the
   *        Apache Software Foundation (http://www.apache.org/)."
   *    Alternately, this acknowlegement may appear in the software itself,
   *    if and wherever such third-party acknowlegements normally appear.
   *
   * 4. The names "The Jakarta Project", "Commons", and "Apache Software
   *    Foundation" must not be used to endorse or promote products derived
   *    from this software without prior written permission. For written
   *    permission, please contact apache@apache.org.
   *
   * 5. Products derived from this software may not be called "Apache"
   *    nor may "Apache" appear in their names without prior written
   *    permission of the Apache Group.
   *
   * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
   * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
   * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
   * DISCLAIMED.  IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
   * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
   * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
   * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
   * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
   * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
   * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
   * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   * SUCH DAMAGE.
   * ====================================================================
   *
   * This software consists of voluntary contributions made by many
   * individuals on behalf of the Apache Software Foundation.  For more
   * information on the Apache Software Foundation, please see
   * <http://www.apache.org/>.
   * 
   * $Id: ChainedBeanCreatorFactory.java,v 1.1 2003/08/21 22:39:00 rdonkin Exp $
   */
  package org.apache.commons.betwixt.io.read;
  
  /**  
    * Group of factory methods for <code>ChainedBeanCreator</code>'s.
    * The standard implementations used by Betwixt are present here.
    *
    * @author Robert Burrell Donkin
    * @version $Revision: 1.1 $
    */
  public class ChainedBeanCreatorFactory {
      
      /** Singleton instance for creating derived beans */
      private static final ChainedBeanCreator derivedBeanCreator 
          = new ChainedBeanCreator() {
              public Object create(
                                  ElementMapping elementMapping, 
                                  ReadContext context, 
                                  BeanCreationChain chain) {
                                  
                  String className = elementMapping.getAttributes().getValue( context.getClassNameAttribute()
);
                  if ( className != null ) {
                      try {
                          // load the class we should instantiate
                          ClassLoader classLoader = context.getClassLoader();
                          if ( classLoader == null ) {
                              context.getLog().warn( 
                              "Could not create derived instance: read context classloader
not set." );
                          }
                          Class clazz = classLoader.loadClass( className );
                          return clazz.newInstance();
                                          
                      } catch (Exception e) {
                          // it would be nice to have a pluggable strategy for exception management
                          context.getLog().warn( "Could not create instance of type: " + className
);
                          context.getLog().debug( "Create new instance failed: ", e );
                          return null;
                      }
                      
                  } else {
                      // pass responsibility down the chain
                      return chain.create( elementMapping, context );
                  }
              }
          };
      
      /**
        * Creates a <code>ChainedBeanCreator</code> that constructs derived beans.
        * These have their classname set by an xml attribute.
        * @return <code>ChainedBeanCreator</code> that implements Derived beans
logic, not null
        */
      public static final ChainedBeanCreator createDerivedBeanCreator() {
          return derivedBeanCreator;
      }
      
      /** Singleton instance that creates beans based on type */
      private static final ChainedBeanCreator elementTypeBeanCreator 
          = new ChainedBeanCreator() {
              public Object create(
                                  ElementMapping element, 
                                  ReadContext context, 
                                  BeanCreationChain chain) {
                                      // create based on type
                  
                  Class theClass = element.getType();
                  try {
  
                      return theClass.newInstance();
                      
                  } catch (Exception e) {
                      // it would be nice to have a pluggable strategy for exception management
                      context.getLog().warn( "Could not create instance of type: " + theClass.getName()
);
                      context.getLog().debug( "Create new instance failed: ", e );
                      return null;
                  }
              }
          }; 
      
      /**
        * Creates a <code>ChainedBeanCreator</code> that constructs beans based
on element type.
        * @return <code>ChainedBeanCreator</code> that implements load by type
beans logic, not null
        */
      public static final ChainedBeanCreator createElementTypeBeanCreator() {
          return elementTypeBeanCreator;
      }
      
      /** Singleton instance that creates beans based on IDREF */
      private static final ChainedBeanCreator idRefBeanCreator 
          = new ChainedBeanCreator() {
              public Object create(
                                  ElementMapping elementMapping, 
                                  ReadContext context, 
                                  BeanCreationChain chain) {
                  if ( context.getMapIDs() ) {
                      String idref = elementMapping.getAttributes().getValue( "idref" );
                      if ( idref != null ) {
                          // XXX need to check up about ordering
                          // XXX this is a very simple system that assumes that 
                          // XXX id occurs before idrefs
                          // XXX would need some thought about how to implement a fuller system
                          context.getLog().trace( "Found IDREF" );
                          Object bean = context.getBean( idref );
                          if ( bean != null ) {
                              if ( context.getLog().isTraceEnabled() ) {
                                  context.getLog().trace( "Matched bean " + bean );
                              }
                              return bean;
                          }
                          context.getLog().trace( "No match found" );
                      }
                  }
                  return chain.create( elementMapping, context );
              }
          }; 
      
      /**
        * Creates a <code>ChainedBeanCreator</code> that finds existing beans
based on their IDREF.
        * @return <code>ChainedBeanCreator</code> that implements IDREF beans
logic, not null
        */
      public static final ChainedBeanCreator createIDREFBeanCreator() {
          return idRefBeanCreator;
      }
  }
  
  
  

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