com.b2international.snowowl.core.api.preferences.io.ConfigurationEntrySerializer.java Source code

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Here is the source code for com.b2international.snowowl.core.api.preferences.io.ConfigurationEntrySerializer.java

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/*
 * Copyright 2011-2015 B2i Healthcare Pte Ltd, http://b2i.sg
 * 
 * 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 com.b2international.snowowl.core.api.preferences.io;

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;

import javax.annotation.Nullable;

import org.osgi.service.prefs.Preferences;

import com.google.common.io.Closeables;

public class ConfigurationEntrySerializer<T> {

    private final Preferences preferences;
    private final String key;
    private final File defaultsFile;

    public ConfigurationEntrySerializer(final Preferences preferences, final String key) {
        this(preferences, key, null);
    }

    public ConfigurationEntrySerializer(final Preferences preferences, final String key, final File defaultsFile) {
        this.preferences = preferences;
        this.key = key;
        this.defaultsFile = defaultsFile;
    }

    public String getKey() {
        return key;
    }

    public final T getDefault() {
        final T defaultFromFile = getDefaultFromFile();
        return (null != defaultFromFile) ? defaultFromFile : computeDefault();
    }

    private final T getDefaultFromFile() {

        if (null == defaultsFile || !defaultsFile.canRead()) {
            return null;
        }

        return new XStreamWrapper(this).fromXML(defaultsFile);
    }

    /**
     * Computes a default value in case a default file is not available.
     * 
     * @return the computed default value; {@code null} by default, subclasses should override
     */
    protected T computeDefault() {
        return null;
    }

    public void serialize(final T entry) {
        preferences.put(key, toXml(entry));
    }

    public String toXml(@Nullable final T entry) {
        return null == entry ? "" : new XStreamWrapper(this).toXML(entry);
    }

    public T deserialize() {

        final String xml = preferences.get(key, null);

        if (xml == null) {
            return getDefault();
        } else {
            return new XStreamWrapper(this).fromXML(xml);
        }
    }

    /**
     * For internal use only; serializes current contents into the defaults file.
     */
    public void serializeDefaults() throws IOException {

        FileOutputStream stream = null;

        try {
            stream = new FileOutputStream(defaultsFile);
            new XStreamWrapper(this).toXML(computeDefault(), stream);
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            Closeables.close(stream, true);
        }
    }
}