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Java example source code file (DiskBasedQueue.java)

This example Java source code file (DiskBasedQueue.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

atomicboolean, concurrentlinkeddeque, diskbasedqueue, file, illegalargumentexception, interruptedexception, ioexception, iterator, object, override, runnable, scheduledexecutorservice, threading, threads, unsupportedoperationexception, util

The DiskBasedQueue.java Java example source code

/*
 *
 *  * Copyright 2015 Skymind,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.deeplearning4j.util;

import org.apache.commons.io.FileUtils;

import java.io.File;
import java.io.IOException;
import java.io.Serializable;
import java.util.Collection;
import java.util.Iterator;
import java.util.Queue;
import java.util.UUID;
import java.util.concurrent.ConcurrentLinkedDeque;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.atomic.AtomicBoolean;

/**
 * Naive disk based queue for storing items on disk.
 * Only meant for poll and adding items.
 * @author Adam Gibson
 */
public class DiskBasedQueue<E> implements Queue,Serializable {

    private File dir;
    private Queue<String> paths = new ConcurrentLinkedDeque<>();
    private ScheduledExecutorService executorService;
    private AtomicBoolean running = new AtomicBoolean(true);
    private Queue<E> save = new ConcurrentLinkedDeque<>();

    public DiskBasedQueue() {
        this(".queue");
    }

    public DiskBasedQueue(String path) {
        this(new File(path));

    }

    public DiskBasedQueue(File dir) {
        this.dir = dir;
        if(!dir.exists()) {
            if(dir.isDirectory())
                throw new IllegalArgumentException("Illegal queue: must be a directory");
        }

        if(!dir.exists())
            dir.mkdirs();
        if(dir.listFiles() != null && dir.listFiles().length > 1)
            try {
                FileUtils.deleteDirectory(dir);
            } catch (IOException e) {
                e.printStackTrace();
            }


        dir.mkdir();


        executorService = Executors.newSingleThreadScheduledExecutor();

        executorService.execute(new Runnable() {
            @Override
            public void run() {
               while(running.get()) {
                while(!save.isEmpty())
                    addAndSave(save.poll());
                   try {
                       Thread.sleep(1000);
                   } catch (InterruptedException e) {
                       Thread.currentThread().interrupt();
                   }
               }
            }
        });
    }

    @Override
    public int size() {
        return paths.size();
    }

    @Override
    public boolean isEmpty() {
        return paths.isEmpty();
    }

    @Override
    public boolean contains(Object o) {
        throw new UnsupportedOperationException();

    }

    @Override
    public Iterator<E> iterator() {
        throw new UnsupportedOperationException();

    }

    @Override
    public Object[] toArray() {
        throw new UnsupportedOperationException();

    }

    @Override
    public <T> T[] toArray(T[] a) {
        throw new UnsupportedOperationException();
    }

    @Override
    public boolean add(E e) {
        save.add(e);
        return true;
    }

    @Override
    public boolean remove(Object o) {
        throw new UnsupportedOperationException();
    }

    @Override
    public boolean containsAll(Collection<?> c) {
        throw new UnsupportedOperationException();
    }

    @Override
    public boolean addAll(Collection<? extends E> c) {
        for(E e : c)
            addAndSave(e);
        return true;
    }

    @Override
    public boolean removeAll(Collection<?> c) {
        throw new UnsupportedOperationException();
    }

    @Override
    public boolean retainAll(Collection<?> c) {
        throw new UnsupportedOperationException();
    }

    @Override
    public void clear() {
        throw new UnsupportedOperationException();
    }

    @Override
    public boolean offer(E e) {
        throw new UnsupportedOperationException();
    }

    @Override
    public E remove() {
        throw new UnsupportedOperationException();
    }

    @Override
    public E poll() {
        String path = paths.poll();
        E ret = SerializationUtils.readObject(new File(path));
        File item = new File(path);
        item.delete();
        return ret;
    }

    @Override
    public E element() {
        throw new UnsupportedOperationException();
    }

    @Override
    public E peek() {
        throw new UnsupportedOperationException();
    }




    private void addAndSave(E e) {
        File path = new File(dir,UUID.randomUUID().toString());
        SerializationUtils.saveObject(e,path);
        paths.add(path.getAbsolutePath());
    }


}

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