com.neocotic.blingaer.common.dao.DAOLocator.java Source code

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Here is the source code for com.neocotic.blingaer.common.dao.DAOLocator.java

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/* Copyright (C) 2011 Alasdair Mercer, http://neocotic.com/
 * 
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 * 
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */
package com.neocotic.blingaer.common.dao;

import org.apache.commons.lang3.ArrayUtils;
import org.apache.commons.lang3.ClassUtils;
import org.apache.commons.lang3.StringUtils;
import org.apache.log4j.Logger;

import com.neocotic.blingaer.common.Locator;
import com.neocotic.blingaer.common.exception.BlingaerRuntimeException;

/**
 * Singleton {@code class} which provides clients with the functionality to
 * lookup {@link DAO} implementations.
 * <p>
 * Clients need to retrieve an instance of this {@code class} and invoke
 * {@link #getDAO(Class)} to get the desired {@code DAO} implementation.
 * 
 * @author Alasdair Mercer
 */
// TODO: Confirm that caching DAO lookups has a negative impact on objectify
public class DAOLocator extends Locator {

    /** The {@code Logger} instance for {@link DAOLocator}. */
    private static final Logger LOG = Logger.getLogger(DAOLocator.class);

    /** The name of the property declaring the datastore to be used. */
    protected static final String DATA_STORE_PROPERTY = "com.neocotic.blingaer.datastore";

    /** The suffix appended to {@link DAO} implementations. */
    protected static final String IMPL_CLASS_SUFFIX = "Impl";

    /** The singleton instance of {@link DAOLocator}. */
    private static DAOLocator instance;

    /**
     * Returns a singleton instance of {@link DAOLocator}.
     * 
     * @return the {@code DAOLocator} instance
     * @throws BlingaerRuntimeException
     *             If datastore property could not be found.
     */
    public static DAOLocator getInstance() throws BlingaerRuntimeException {
        if (instance == null) {
            instance = new DAOLocator();
        }

        return instance;
    }

    private String dataStore;

    /**
     * Prevents external invocation to support singleton pattern.
     * 
     * @throws BlingaerRuntimeException
     *             If datastore property could not be found.
     */
    DAOLocator() throws BlingaerRuntimeException {
        dataStore = StringUtils.trimToNull(System.getProperty(DATA_STORE_PROPERTY));

        if (dataStore == null) {
            throw new BlingaerRuntimeException("Could not locate datastore property: " + DATA_STORE_PROPERTY);
        }
    }

    /**
     * Retrieves the POJO implementation of the {@link DAO} {@code class}
     * provided.
     * <p>
     * Reflection is used to lookup the POJO implementation and delegate calls
     * to it.
     * 
     * @param cls
     *            the {@code DAO class} whose POJO implementation is to be
     *            located
     * @return the POJO implementation of the specified {@code class}
     * @throws BlingaerRuntimeException
     *             If an error occurs while loading/instantiating the new
     *             {@code Service class}.
     */
    @SuppressWarnings("unchecked")
    public <T extends DAO> T getDAO(Class<T> cls) throws BlingaerRuntimeException {
        LOG.trace("Entered method - getDAO");

        String className = cls.getName() + IMPL_CLASS_SUFFIX;

        // Injects datastore package name in to
        String[] arr = StringUtils.split(className, ClassUtils.PACKAGE_SEPARATOR_CHAR);
        arr = ArrayUtils.add(arr, arr.length - 1, dataStore);
        className = StringUtils.join(arr, ClassUtils.PACKAGE_SEPARATOR_CHAR);

        DAO impl = newDAOImpl(className);

        /*
         * Currently not caching these results as I'm not sure if it will have a
         * negative affect on objectify
         */

        LOG.trace("Exiting method - getDAO");

        return (T) impl;
    }

    /**
     * Creates a new instance of the {@link DAO} implementation {@code class}.
     * 
     * @param className
     *            the name of the {@code class} to be loaded and instantiated
     * @return an instance of the specified {@code class}
     * @throws BlingaerRuntimeException
     *             If an error occurs while loading/instantiating the new
     *             {@code Service class}.
     */
    private DAO newDAOImpl(String className) throws BlingaerRuntimeException {
        LOG.trace("Entered method - newDAO");

        DAO dao = null;

        try {
            dao = (DAO) getDefaultClassLoader().loadClass(className).newInstance();
        } catch (Exception e) {
            LOG.error("Throwing exception", e);

            throw new BlingaerRuntimeException(e);
        }

        LOG.trace("Exiting method - newDAO");

        return dao;
    }
}