/**
* 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
*
* 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.
*/
package org.drools.base.accumulators;
import java.io.Externalizable;
import java.io.IOException;
import java.io.ObjectInput;
import java.io.ObjectOutput;
import java.io.Serializable;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
/**
* <p>An implementation of an accumulator capable of collecting lists of values.
* This is similar to the "collect" CE, but allows us to collect any value, not
* only facts.</p>
*
* <p>Example:</p>
* <pre>
* rule "List employee names"
* when
* $names : List() from accumulate(
* Employee( $n : firstName, $l : lastName ),
* collectList( $n + " " + $l ) )
* then
* // do something
* end
* </pre>
*
* <p>The list accepts duplications and the order of the elements in the list is not
* guaranteed.</p>
*
* @author etirelli
*
*/
public class CollectListAccumulateFunction
implements
AccumulateFunction {
public void readExternal(ObjectInput in) throws IOException,
ClassNotFoundException {
// functions are stateless, so nothing to serialize
}
public void writeExternal(ObjectOutput out) throws IOException {
// functions are stateless, so nothing to serialize
}
public static class CollectListData
implements
Externalizable {
public List< Object > list = new ArrayList<Object>();
public CollectListData() {
}
@SuppressWarnings("unchecked")
public void readExternal(ObjectInput in) throws IOException,
ClassNotFoundException {
list = (List< Object >) in.readObject();
}
public void writeExternal(ObjectOutput out) throws IOException {
out.writeObject( list );
}
}
/* (non-Javadoc)
* @see org.drools.base.accumulators.AccumulateFunction#createContext()
*/
public Serializable createContext() {
return new CollectListData();
}
/* (non-Javadoc)
* @see org.drools.base.accumulators.AccumulateFunction#init(java.lang.Object)
*/
public void init(Serializable context) throws Exception {
CollectListData data = (CollectListData) context;
data.list.clear();
}
/* (non-Javadoc)
* @see org.drools.base.accumulators.AccumulateFunction#accumulate(java.lang.Object, java.lang.Object)
*/
public void accumulate(Serializable context,
Object value) {
CollectListData data = (CollectListData) context;
data.list.add( value );
}
/* (non-Javadoc)
* @see org.drools.base.accumulators.AccumulateFunction#reverse(java.lang.Object, java.lang.Object)
*/
public void reverse(Serializable context,
Object value) throws Exception {
CollectListData data = (CollectListData) context;
data.list.remove( value );
}
/* (non-Javadoc)
* @see org.drools.base.accumulators.AccumulateFunction#getResult(java.lang.Object)
*/
public Object getResult(Serializable context) throws Exception {
CollectListData data = (CollectListData) context;
return Collections.unmodifiableList( data.list );
}
/* (non-Javadoc)
* @see org.drools.base.accumulators.AccumulateFunction#supportsReverse()
*/
public boolean supportsReverse() {
return true;
}
}