name.martingeisse.common.util.TemporaryFolder.java Source code

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Here is the source code for name.martingeisse.common.util.TemporaryFolder.java

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/**
 * Copyright (c) 2010 Martin Geisse
 *
 * This file is distributed under the terms of the MIT license.
 */

package name.martingeisse.common.util;

import java.io.File;
import java.io.IOException;
import org.apache.commons.io.FileUtils;

/**
 * Each instance of this class corresponds to a temporary folder for
 * arbitrary purposes. The folder is created by the constructor and
 * removed with dispose(). No automatic removal is done, so clients
 * should use a try/finally block to ensure disposal, unless the folder
 * is intentionally kept (e.g. for diagnostic purposes).
 * 
 * The temporary folder is created as a subfolder of /var/projects/temp/app,
 * where the "app" suffix is application-specific to separate temp folders from
 * different applications. This class must be statically initialized with that
 * folder name once before usage. 
 * 
 * This class expects /var/projects/temp to exist. The application-specific
 * subfolder is re-created cleanly on initialization.
 */
public class TemporaryFolder {

    /**
     * the applicationFolder
     */
    private static File applicationFolder = null;

    /**
     * the count
     */
    private static long count = 0;

    /**
     * the instanceId
     */
    private long instanceId;

    /**
     * the instanceFolder
     */
    private File instanceFolder;

    /**
     * Initializes the temporary folder system for the specified application.
     * The application identifier is used as the name of the subfolder inside
     * /var/projects/temp.
     * @param applicationIdentifier the application-specific identifier / folder name
     */
    public static synchronized void initialize(String applicationIdentifier) {
        applicationFolder = new File("/var/projects/temp/" + applicationIdentifier);
        try {
            FileUtils.deleteDirectory(applicationFolder);
        } catch (IOException e) {
            throw new RuntimeException(
                    "cannot delete previous temporary application folder: " + applicationFolder.getAbsolutePath());
        }
        if (!applicationFolder.mkdir()) {
            throw new RuntimeException(
                    "cannot create temporary application folder: " + applicationFolder.getAbsolutePath());
        }
    }

    /**
     * Allocates a sequential ID number for an instance folder.
     * @return the id number
     */
    private static synchronized long allocateId() {
        final long id = count;
        count++;
        return id;
    }

    /**
     * Constructor.
     */
    public TemporaryFolder() {
        this.instanceId = allocateId();
        this.instanceFolder = new File(applicationFolder, "x" + instanceId);
        if (!instanceFolder.mkdir()) {
            throw new RuntimeException("cannot create temporary folder: " + instanceFolder.getAbsolutePath());
        }
    }

    /**
     * Getter method for the instanceId.
     * @return the instanceId
     */
    public long getInstanceId() {
        return instanceId;
    }

    /**
     * Getter method for the instanceFolder.
     * @return the instanceFolder
     */
    public File getInstanceFolder() {
        return instanceFolder;
    }

    /**
     * Disposes of this folder. The id property is still valid after disposal,
     * but the temporary folder itself is gone.
     */
    public void dispose() {
        try {
            FileUtils.deleteDirectory(instanceFolder);
        } catch (IOException e) {
            throw new RuntimeException("cannot delete temporary folder: " + instanceFolder.getAbsolutePath());
        }
        instanceFolder = null;
    }

}