/*
 * Copyright 1999-2002,2004 The Apache Software Foundation.
 * 
 * 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 org.apache.struts.webapp.example2;


/**
 * <p>A <strong>Data Access Object</strong> (DAO) interface describing
 * the available operations for retrieving and storing {@link User}s
 * (and their associated {@link Subscription}s) in some persistence layer
 * whose characteristics are not specified here.  One or more implementations
 * will be created to perform the actual I/O that is required.</p>
 *
 * @author Craig R. McClanahan
 * @version $Rev: 54934 $ $Date: 2004-10-16 18:07:50 +0100 (Sat, 16 Oct 2004) $
 * @since Struts 1.1
 */

public interface UserDatabase {


    // --------------------------------------------------------- Public Methods


    /**
     * <p>Create and return a new {@link User} defined in this user database.
     * </p>
     *
     * @param username Username of the new user
     *
     * @exception IllegalArgumentExceptionif the specified username
     *  is not unique
     */
    public User createUser(String username);


    /**
     * <p>Finalize access to the underlying persistence layer.</p>
     *
     * @exception Exception if a database access error occurs
     */
    public void close() throws Exception;


    /**
     * <p>Return the existing {@link User} with the specified username,
     * if any; otherwise return <code>null</code>.</p>
     *
     * @param username Username of the user to retrieve
     */
    public User findUser(String username);


    /**
     * <p>Return the set of {@link User}s defined in this user database.</p>
     */
    public User[] findUsers();


    /**
     * <p>Initiate access to the underlying persistence layer.</p>
     *
     * @exception Exception if a database access error occurs
     */
    public void open() throws Exception;


    /**
     * Remove the specified {@link User} from this database.
     *
     * @param user User to be removed
     *
     * @exception IllegalArgumentException if the specified user is not
     *  associated with this database
     */
    public void removeUser(User user);


    /**
     * <p>Save any pending changes to the underlying persistence layer.</p>
     *
     * @exception Exception if a database access error occurs
     */
    public void save() throws Exception;


}