/*
 * $Header: /home/cvs/commons/dbutils-1.0/ja/src/org/apache/commons/dbutils/QueryLoader.java,v 1.1.1.1 2004/02/13 10:02:04 hioki Exp $
 * $Revision: 1.1.1.1 $
 * $Date: 2004/02/13 10:02:04 $
 * 
 * ====================================================================
 *
 * The Apache Software License, Version 1.1
 *
 * Copyright (c) 2003 The Apache Software Foundation.  All rights
 * reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * 3. The end-user documentation included with the redistribution, if
 *    any, must include the following acknowledgement:
 *       "This product includes software developed by the
 *        Apache Software Foundation (http://www.apache.org/)."
 *    Alternately, this acknowledgement may appear in the software itself,
 *    if and wherever such third-party acknowledgements normally appear.
 *
 * 4. The names "The Jakarta Project", "Commons", and "Apache Software
 *    Foundation" must not be used to endorse or promote products derived
 *    from this software without prior written permission. For written
 *    permission, please contact apache@apache.org.
 *
 * 5. Products derived from this software may not be called "Apache"
 *    nor may "Apache" appear in their names without prior written
 *    permission of the Apache Software Foundation.
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED.  IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
 * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 *
 */

package org.apache.commons.dbutils;

import java.io.IOException;
import java.io.InputStream;
import java.util.HashMap;
import java.util.Map;
import java.util.Properties;

/**
 * <code>QueryLoader</code> は、SQL文をマップさせた問い合わせ名称を満たすプロパティファイルを読み込みます。 
 * 問い合わせ一式の登録処理を行うため、同一の問い合わせ名称で重複するコピー内容はメモリへ読み込まれません。 
 * このクラスはスレッドセーフです。
 * {@primary <code>QueryLoader</code> loads properties files filled with query name to 
 * SQL mappings.  It acts as a registry for sets of queries so that multiple 
 * copies of the same queries aren't loaded into memory.  This class is thread
 * safe.}
 * 
 * @author David Graham
 * @translator 小川 環
 * @editor 日置 聡
 * @status underproof
 * @update 2003/12/22
 */
public class QueryLoader {

    /**
     * The Singleton instance of this class.
     */
    private static final QueryLoader instance = new QueryLoader();

    /**
     * このクラスのインスタンスを返します。
     * {@primary Return an instance of this class.}
     * @return Singletonインスタンス。
     * {@primary The Singleton instance.}
     */
    public static QueryLoader instance() {
        return instance;
    }

    /**
     * Maps query set names to Maps of their queries.
     */
    private Map queries = new HashMap();

    /**
     * QueryLoader のコンストラクタ。
     * {@primary QueryLoader constructor.}
     */
    protected QueryLoader() {
        super();
    }

    /**
     * 問い合わせ名称とSQL文の値が対応付けられたMapを読み込みます。
     * 当該 Map はキャッシュ化され、同じパスから読み込まれた後に要求されると、キャッシュされた Map が返されます。 
     * {@primary Loads a Map of query names to SQL values.  The Maps are cached so a 
     * subsequent request to load queries from the same path will return
     * the cached Map.}
     * 
     * @param path クラスローダがファイルを検索するのに使用するパス。
     * これはファイルシステムのパスでは<strong>ありません</strong>。
     * JAR化されたcom.yourcorp.app.jdbcパッケージのQueries.propertiesファイルを配置した場合、 このメソッドに
     * "/com/yourcorp/app/jdbc/Queries.properties" を渡してください。 
     * {@primary The path that the ClassLoader will use to find the file. 
     * This is <strong>not</strong> a file system path.  If you had a jarred
     * Queries.properties file in the com.yourcorp.app.jdbc package you would 
     * pass "/com/yourcorp/app/jdbc/Queries.properties" to this method.}
     * @throws IOException
     * @throws IllegalArgumentException 指定したパス上でクラスローダがファイルを見つけられなかった場合。
     * {@primary if the ClassLoader can't find a file at the given path.}
     */
    public synchronized Map load(String path) throws IOException {

        Map queryMap = (Map) this.queries.get(path);

        if (queryMap == null) {
            queryMap = this.loadQueries(path);
            this.queries.put(path, queryMap);
        }

        return queryMap;
    }

    /**
     * Loads a properties file into a Map object.
     * @param path The path that the ClassLoader will use to find the file.
     * @throws IOException
     */
    private Map loadQueries(String path) throws IOException {
        InputStream in = QueryLoader.class.getResourceAsStream(path);

        if (in == null) {
            throw new IllegalArgumentException(path + " not found.");
        }

        Properties props = new Properties();
        props.load(in);

        // Copy to HashMap for better performance
        return new HashMap(props);
    }
    
    /**
     * 指定したパスに対応する問い合わせをキャッシュされたMapから削除します。
     * {@primary Removes the queries for the given path from the cache.}
     * @param path 問い合わせが読み込まれたパス。
     * {@primary The path that the queries were loaded from.}
     */
    public synchronized void unload(String path){
        this.queries.remove(path);
    }

}