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   * Copyright 2010 JBoss Inc
   * Licensed 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
  * 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.
 package org.drools;

This class is used to provide a ChangeSet info to a ResourceChangeNotifier. It should be used when you implement the ResourceChangeMonitor interface. Each method provides a Collection of removed, added and modified resources, and determined by the monitor. Drools currently only provides the ResourceChangeScanner, which scans the local disk for changes. The scanning only works with the ChangeSet is applied to a KnowledgeAgent, and not a KnowledgeBase.

The xml format has a root level <change-set> element and then it can contain <add>, <modified>, <removed> elements - each one can only be used once. add, modified, removed then contain a list of <resource> elements. Resources may take a configuration, currently only decision table resources use that.

KnowledgeBuilder currently ignores Added/Modified xml elements, the KnowledgeAgent will use them, when rebuilding the KnowledgeBase.

 <change-set xmlns=''
             xs:schemaLocation='' >
       <resource source='http:org/domain/myrules.drl' type='DRL' />
       <resource source='classpath:data/IntegrationExampleTest.xls' type="DTABLE">
           <decisiontable-conf input-type="XLS" worksheet-name="Tables_2" />
       <resource source='file:org/drools/decisiontable/myflow.drf' type='DRF' />

Notice that each resource defines a protocol for it's source, this is because when using a ChangeSet all resource elements are turned into a URL instance, so it obeys the format as provided by the JDK URL class. There is one exception which is the classpath protocol, which is handled separately. Here the resource is loaded from the classpath, where it uses the default ClassLoader of the KnowledgeBase.

A path, when using file based protocols, can point to a folder. In such a situation all the resources in that folder will be added. When used with a KnowledgeAgent, which is also set to scan directories, it will continue to scan the directory for new or removed resources.

The ChangeSet can be used as a ResourceType with the KnowledgeBuilder or applied directly to a KnowledgeAgent.

Example showing a changeset being used with a KnowledgeBuilder:

 KnowledgeBuilder kbuilder = KnowledgeBuilderFactory.newKnowledgeBuilder();
 kbuilder.add( ResourceFactory.newUrlResource( url ),
               ResourceType.ChangeSet );

Example showing a changeset being applied to a KnowledgeAgent:

 KnowledgeAgent kagent = KnowledgeAgentFactory.newKnowledgeAgent( "MyAgent" );
 kagent.applyChangeSet( ResourceFactory.newUrlResource( url ) );
 KnowledgeBase kbase = kagent.getKnowledgeBase();

This interface, as well as ResourceChangeMonitor, ResourceChangeNotifier, ResourceChangeScanner and ResourceChangeListener are still considered subject to change. Use the XML format change-set, as part of the ResourceType api when adding to KnowledgeBuilder, which is considered stable.

 public interface ChangeSet {
Returns an immutable Collection of removed Resources for this ChangeSet

     public Collection<ResourcegetResourcesRemoved();

Returns an immutable Collection of added Resources for this ChangeSet

     public Collection<ResourcegetResourcesAdded();

Returns an immutable Collection of modified Resources for this ChangeSet

     public Collection<ResourcegetResourcesModified();

Returns a collection containing the full names (package+name) of the kdefinitions to be removed.

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