zkoss/zk

/* ResourceLoader.java

    Purpose:
        
    Description:
        
    History:
        Tue Aug 30 18:31:26     2005, Created by tomyeh

Copyright (C) 2005 Potix Corporation. All Rights Reserved.

{{IS_RIGHT
    This program is distributed under LGPL Version 2.1 in the hope that
    it will be useful, but WITHOUT ANY WARRANTY.
}}IS_RIGHT
*/
package org.zkoss.web.util.resource;

import java.io.File;
import java.io.FileNotFoundException;
import java.net.URL;
import java.net.URLConnection;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import org.zkoss.util.resource.Loader;

/**
 * A semi-implemented loader to used with {@link ResourceCaches#get}
 * to retrieve servlet resources.
 *
 * @author tomyeh
 */
public abstract class ResourceLoader<V> implements Loader<ResourceInfo, V> {
    private static final Logger log = LoggerFactory.getLogger(ResourceLoader.class);

    protected ResourceLoader() {
    }

    /** Parses the specified file and returns the result which
     * will be stored into the cache ({@link ResourceCaches#get}).
     *
     * <p>Deriving must override this method.
     *
     * @param extra the extra parameter passed from {@link ResourceCaches#get}.
     */
    protected abstract V parse(String path, File file, Object extra) throws Exception;

    /** Parses the specified URL and returns the result which
     * will be stored into the cache ({@link ResourceCaches#get}).
     *
     * <p>Deriving must override this method.
     *
     * @param extra the extra parameter passed from {@link ResourceCaches#get}.
     */
    protected abstract V parse(String path, URL url, Object extra) throws Exception;

    public boolean shallCheck(ResourceInfo src, long expiredMillis) {
        return expiredMillis > 0;
        //FUTURE: prolong if src.url's protocol is http, https or ftp
    }

    public long getLastModified(ResourceInfo src) {
        if (src.url != null) {
            URLConnection conn = null;
            try {
                URL url = src.url;
                // prevent SSRF warning
                url = new URL(url.getProtocol(), url.getHost(), url.getPort(), url.getFile());
                conn = url.openConnection();
                final long v = conn.getLastModified();
                return v != -1 ? v : 0; //not to reload (5.0.6 for better performance)
            } catch (Throwable ex) {
                return -1; //reload (might be removed)
            } finally {
                if (conn != null) {
                    try {
                        conn.getInputStream().close();
                    } catch (Throwable e) {
                        log.warn("The connection cannot be closed", e);
                    }
                }
            }
        }

        final long v = src.file.lastModified();
        return v == -1 ? 0
                : //not to reload if unknown (5.0.6 for better performance)
                v == 0 ? -1 : v; //0 means nonexistent so reload
    }

    public V load(ResourceInfo src) throws Exception {
        if (src.url != null)
            return parse(src.path, src.url, src.extra);

        // Bug ZK-1132
        if (!src.file.exists() && src.extra != null
                && ((ServletContextLocator) src.extra).getResourceAsStream(src.path) == null) {
            if (log.isDebugEnabled())
                log.debug("Not found: " + src.file);
            return null; //File not found
        }

        if (log.isDebugEnabled())
            log.debug("Loading " + src.file);
        try {
            return parse(src.path, src.file, src.extra);
        } catch (FileNotFoundException ex) {
            return null;
        }
    }
}