de.rnd7.urlcache.URLCacheLoader.java Source code

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Here is the source code for de.rnd7.urlcache.URLCacheLoader.java

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/**
 * Copyright 2016 Philipp Arndt
 *
 * 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 de.rnd7.urlcache;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.util.Optional;

import org.apache.commons.io.IOUtils;

import com.google.common.cache.CacheLoader;

final class URLCacheLoader extends CacheLoader<URLCacheKey, CachedElement> {

    private final File cacheFolder;

    public URLCacheLoader(final File cacheFolder) {
        this.cacheFolder = cacheFolder;
    }

    @Override
    public CachedElement load(final URLCacheKey key) throws Exception {
        final Optional<CachedElement> fromDisk = this.loadFromDisk(key);
        if (fromDisk.isPresent()) {
            return fromDisk.get();
        }

        final CachedElement element = this.loadFromURL(key);
        this.saveToDisk(element, key);

        return element;
    }

    private void saveToDisk(final CachedElement element, final URLCacheKey key) throws IOException {
        final File localFile = this.toLocalFile(key);

        try (FileOutputStream fos = new FileOutputStream(localFile);
                ObjectOutputStream out = new ObjectOutputStream(fos);) {

            out.writeObject(element);
            out.flush();
        }
    }

    private CachedElement loadFromURL(final URLCacheKey key) throws IOException {
        final CachedElement element = new CachedElement();
        element.setBytes(IOUtils.toByteArray(key.getUrl()));
        element.setValidUntil(CachedElement.createTimeoutDate());

        return element;
    }

    private File toLocalFile(final URLCacheKey key) {
        return new File(this.cacheFolder, key.getKey());
    }

    private Optional<CachedElement> loadFromDisk(final URLCacheKey key) throws IOException {
        final File localFile = this.toLocalFile(key);

        Optional<CachedElement> result = Optional.empty();

        if (localFile.exists()) {
            try (final InputStream in = new FileInputStream(localFile);
                    final ObjectInputStream objIn = new ObjectInputStream(in);) {

                final CachedElement element = (CachedElement) objIn.readObject();
                result = Optional.of(element);
            } catch (final ClassNotFoundException e) {
                throw new IOException(e);
            }
        }

        if (result.isPresent()) {
            if (!result.get().isValid()) {
                localFile.delete();
                result = Optional.empty();
            }
        }

        return result;
    }

}