ImageStorage.java

package org.wahlzeit.model.persistence;

import org.wahlzeit.model.PhotoSize;
import org.wahlzeit.services.LogBuilder;

import java.io.IOException;
import java.io.Serializable;
import java.security.InvalidParameterException;
import java.util.logging.Logger;

/**
 * Abstract super class that offers a convenient interface for all kinds of storage types to store images.
 * 
 * @review
 */
public abstract class ImageStorage {

	private static final Logger log = Logger.getLogger(ImageStorage.class.getName());
	private static ImageStorage instance = null;

	/**
	 * @methodtype get
	 */
	public static ImageStorage getInstance()
			throws NullPointerException {

		if (instance == null) {
			throw new NullPointerException("Image storage instance is null, call setInstance() first!");
		}
		return instance;
	}

	/**
	 * @methodtype set
	 */
	public static void setInstance(ImageStorage newInstance) {
		log.config(LogBuilder.createSystemMessage().
				addAction("set ImageStorage instance").
				addParameter("instance", newInstance).toString());
		instance = newInstance;
	}


	// write-methods ---------------------------------------------------------------------------------------------------

	/**
	 * Writes the image to the storage, so you can access it via photoId and size again. An existing file with that
	 * parameter is overwritten.
	 *
	 * @methodtype command
	 * @methodproperty wrapper
	 */
	public void writeImage(Serializable image, String photoIdAsString, int size)
			throws InvalidParameterException, IOException {

		assertImageNotNull(image);
		assertValidPhotoId(photoIdAsString);
		PhotoSize.assertIsValidPhotoSizeAsInt(size);

		log.config(LogBuilder.createSystemMessage().
				addAction("write image to storage").
				addParameter("image", image).
				addParameter("photo id", photoIdAsString).
				addParameter("size", size).toString());

		doWriteImage(image, photoIdAsString, size);
	}

	/**
	 * Actually writes the image to the storage
	 *
	 * @methodtype command
	 * @methodproperty hook
	 */
	protected abstract void doWriteImage(Serializable image, String photoIdAsString, int size)
			throws IOException, InvalidParameterException;


	// read methods ----------------------------------------------------------------------------------------------------

	/**
	 * Reads an image from storage via photoId and the size. When the image is not found, null is returned.
	 *
	 * @methodtype get
	 * @methodproperty convenience
	 */
	public Serializable readImage(String photoIdAsString, int size)
			throws IllegalArgumentException, IOException {

		assertValidPhotoId(photoIdAsString);
		PhotoSize.assertIsValidPhotoSizeAsInt(size);

		log.config(LogBuilder.createSystemMessage().
				addAction("read image from storage").
				addParameter("photo id", photoIdAsString).
				addParameter("size", size).toString());

		return doReadImage(photoIdAsString, size);
	}

	/**
	 * Actually reads the specified file from the storage. When not found, null is returned.
	 *
	 * @methodtype get
	 * @methodproperty hook
	 */
	protected abstract Serializable doReadImage(String filename, int size)
			throws IOException;


	// exist method ----------------------------------------------------------------------------------------------------

	/**
	 * Checks if the specified image already exists in the storage
	 *
	 * @methodtype boolean query
	 * @methodproperty wrapper
	 */
	public boolean doesImageExist(String photoIdAsString, int size)
			throws IllegalArgumentException {

		assertValidPhotoId(photoIdAsString);
		PhotoSize.assertIsValidPhotoSizeAsInt(size);

		log.config(LogBuilder.createSystemMessage().
				addAction("check if image exists in storage").
				addParameter("photo id", photoIdAsString).
				addParameter("size", size).toString());

		return doDoesImageExist(photoIdAsString, size);
	}


	/**
	 * Actually checks if the specified image already exists in the storage
	 *
	 * @methodtype boolean query
	 * @methodproperty hook
	 */
	protected abstract boolean doDoesImageExist(String photoIdAsString, int size);


	// assertion methods -----------------------------------------------------------------------------------------------

	/**
	 * @methodtype assert
	 */
	protected void assertImageNotNull(Serializable image)
			throws IllegalArgumentException {

		if (image == null) {
			throw new IllegalArgumentException("Image is null!");
		}
	}

	/**
	 * @methodtype assert
	 */
	protected void assertValidPhotoId(String photoId)
			throws IllegalArgumentException {

		if (photoId == null || "".equals(photoId)) {
			throw new IllegalArgumentException("Invalid photoId:" + photoId);
		}
	}
}