/*
* Copyright 2002-2011 the original author or authors.
*
* 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.springframework.integration.util;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.List;
/**
* An implementation of {@link CollectionFilter} that remembers the elements passed in
* the previous invocation in order to avoid returning those elements more than once.
*
* @author Mark Fisher
* @since 2.1
*/
public class AcceptOnceCollectionFilter<T> implements CollectionFilter<T> {
private volatile Collection<T> lastSeenElements = Collections.emptyList();
public synchronized Collection<T> filter(Collection<T> unfilteredElements) {
List<T> filteredElements = new ArrayList<T>();
for (T element : unfilteredElements) {
if (!this.lastSeenElements.contains(element)) {
filteredElements.add(element);
}
}
this.lastSeenElements = unfilteredElements;
return filteredElements;
}
}