ResourceLoader.java

/**************************************************************************************
 * Copyright (C) 2008 EsperTech, Inc. All rights reserved.                            *
 * http://esper.codehaus.org                                                          *
 * http://www.espertech.com                                                           *
 * ---------------------------------------------------------------------------------- *
 * The software in this package is published under the terms of the GPL license       *
 * a copy of which has been included with this distribution in the license.txt file.  *
 **************************************************************************************/
package com.espertech.esper.util;

import com.espertech.esper.client.EPException;

import java.net.URL;
import java.net.MalformedURLException;

/**
 * Utility class for loading or resolving external resources via URL and class path.
 */
public class ResourceLoader
{
    /**
     * Resolve a resource into a URL using the URL string or classpath-relative filename and
     * using a name for any exceptions thrown.
     * @param resourceName is the name for use in exceptions
     * @param urlOrClasspathResource is a URL string or classpath-relative filename
     * @return URL or null if resolution was unsuccessful
     */
    public static URL resolveClassPathOrURLResource(String resourceName, String urlOrClasspathResource)
    {
        URL url;
        try
        {
            url = new URL(urlOrClasspathResource);
        }
        catch (MalformedURLException ex)
        {
            url = getClasspathResourceAsURL(resourceName, urlOrClasspathResource);
        }
        return url;
    }

    /**
     * Returns an URL from an application resource in the classpath.
     * <p>
     * The method first removes the '/' character from the resource name if
     * the first character is '/'.
     * <p>
     * The lookup order is as follows:
     * <p>
     * If a thread context class loader exists, use <tt>Thread.currentThread().getResourceAsStream</tt>
     * to obtain an InputStream.
     * <p>
     * If no input stream was returned, use the <tt>Configuration.class.getResourceAsStream</tt>.
     * to obtain an InputStream.
     * <p>
     * If no input stream was returned, use the <tt>Configuration.class.getClassLoader().getResourceAsStream</tt>.
     * to obtain an InputStream.
     * <p>
     * If no input stream was returned, throw an Exception.
     *
     * @param resourceName is the name for use in exceptions
     * @param resource is the classpath-relative filename to resolve into a URL
     * @return URL for resource
     */
    public static URL getClasspathResourceAsURL(String resourceName, String resource)
    {
        String stripped = resource.startsWith("/") ?
                resource.substring(1) : resource;

        URL url = null;
        ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
        if (classLoader != null) {
            url = classLoader.getResource(stripped);
        }
        if (url == null) {
            url = ResourceLoader.class.getResource(resource);
        }
        if (url == null) {
            url = ResourceLoader.class.getClassLoader().getResource(stripped);
        }
        if (url == null ) {
            throw new EPException(resourceName + " resource '" + resource + "' not found");
        }
        return url;
    }



}