/*
* Copyright 2002-2016 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.file;
import java.io.File;
import java.util.Arrays;
import java.util.List;
import org.springframework.integration.file.filters.CompositeFileListFilter;
import org.springframework.integration.file.filters.FileListFilter;
/**
* A custom scanner that only returns the first <code>maxNumberOfFiles</code>
* elements from a directory listing. This is useful to limit the number of File
* objects in memory and therefore mutually exclusive with {@code AcceptOnceFileListFilter}.
* It should not be used in conjunction with an {@code AcceptOnceFileListFilter}.
*
* @author Iwein Fuld
* @author Gary Russell
* @since 2.0
*/
public class HeadDirectoryScanner extends DefaultDirectoryScanner {
private final HeadFilter headFilter;
public HeadDirectoryScanner(int maxNumberOfFiles) {
HeadFilter headFilter = new HeadFilter(maxNumberOfFiles);
this.headFilter = headFilter;
this.setFilter(headFilter);
}
@Override
public final void setFilter(FileListFilter<File> filter) {
if (filter instanceof CompositeFileListFilter) {
((CompositeFileListFilter<File>) filter).addFilter(this.headFilter);
super.setFilter(filter);
}
else {
CompositeFileListFilter<File> compositeFilter = new CompositeFileListFilter<File>();
compositeFilter.addFilter(filter).addFilter(this.headFilter);
super.setFilter(compositeFilter);
}
}
private static final class HeadFilter implements FileListFilter<File> {
private final int maxNumberOfFiles;
private HeadFilter(int maxNumberOfFiles) {
this.maxNumberOfFiles = maxNumberOfFiles;
}
@Override
public List<File> filterFiles(File[] files) {
return Arrays.asList(files).subList(0, Math.min(files.length, this.maxNumberOfFiles));
}
}
}