FileTreeIterator.java

/*
 * (C) Copyright 2006-2016 Nuxeo SA (http://nuxeo.com/) and others.
 *
 * 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.
 * 
 * Contributors:
 *     bstefanescu
 */
package org.nuxeo.common.utils;

import java.io.File;
import java.io.FileFilter;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.NoSuchElementException;
import java.util.Queue;

/**
 * @author <a href="mailto:bs@nuxeo.com">Bogdan Stefanescu</a>
 */
public class FileTreeIterator implements Iterator<File> {

    private final Queue<Iterator<File>> queue = new LinkedList<>();

    private File file; // last iterated file

    private FileFilter filter;

    public FileTreeIterator(File root) {
        queue.add(new OneFileIterator(root));
    }

    public FileTreeIterator(File root, boolean excludeRoot) {
        if (excludeRoot) {
            queue.add(new LazyChildrenIterator(root));
        } else {
            queue.add(new OneFileIterator(root));
        }
    }

    public void setFilter(FileFilter filter) {
        this.filter = filter;
    }

    public FileFilter getFilter() {
        return filter;
    }

    public boolean hasNext() {
        if (queue.isEmpty()) {
            return false;
        }
        Iterator<File> it = queue.peek();
        if (it.hasNext()) {
            return true;
        } else {
            queue.poll();
            return hasNext();
        }
    }

    public File next() {
        if (!hasNext()) {
            throw new NoSuchElementException("No more files to iterate over");
        }
        file = queue.peek().next();
        if (file.isDirectory()) {
            queue.add(new LazyChildrenIterator(file));
        }
        return file;
    }

    public void remove() {
        if (file == null) {
            throw new IllegalStateException("there is no current file to delete");
        }
        org.apache.commons.io.FileUtils.deleteQuietly(file);
    }

    // we don't fulfill iterator contract - we don't need a real iterator,
    // this is used only internally
    private static class OneFileIterator implements Iterator<File> {

        private File file;

        private OneFileIterator(File file) {
            this.file = file;
        }

        public boolean hasNext() {
            return file != null;
        }

        public File next() {
            File next = file;
            file = null;
            return next;
        }

        public void remove() {
            throw new UnsupportedOperationException("remove not supported");
        }
    }

    // we don't fulfill iterator contract - we don't need a real iterator,
    // this is used only internally
    private class LazyChildrenIterator implements Iterator<File> {

        private final File dir;

        private File[] children;

        private int pos = -1; // last pos

        private LazyChildrenIterator(File dir) {
            this.dir = dir;
        }

        public boolean hasNext() {
            if (children == null) {
                children = filter == null ? dir.listFiles() : dir.listFiles(filter);
                if (children == null) {
                    return false; // not a dir
                }
                return children.length > 0;
            } else {
                return pos < children.length - 1;
            }
        }

        public File next() {
            return children[++pos];
        }

        public void remove() {
            throw new UnsupportedOperationException("remove not supported");
        }
    }

    public static void main(String[] args) {
        FileTreeIterator it = new FileTreeIterator(new File("/root/kits"), false);
        while (it.hasNext()) {
            System.out.println(">> " + it.next());
        }
    }

}