src/org/jsecurity/util/ResourceUtils.java

/*
 * Copyright 2005-2008 Jeremy Haile
 *
 * 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.jsecurity.util;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.URL;

/**
 * Static helper methods for loading resources.
 *
 * @since 0.2
 * @author Jeremy Haile
 */
public class ResourceUtils {

    /** Resource path prefix that specifies to load from a classpath location, value is <b><code>classpath:</code></b> */
    public static final String CLASSPATH_PREFIX = "classpath:";
    /** Resource path prefix that specifies to load from a url location, value is <b><code>url:</code></b> */
    public static final String URL_PREFIX = "url:";
    /** Resource path prefix that specifies to load from a file location, value is <b><code>file:</code></b> */
    public static final String FILE_PREFIX = "file:";

    /**
     * Commons-logging logger
     */
    private final static transient Log logger = LogFactory.getLog( ResourceUtils.class );    


    /**
     * Prevent instantiation.
     */
    private ResourceUtils() { }


    /**
     * Returns the InputStream for the resource represented by the specified path.
     *
     * <p>The supporting prefixes are defined as as *_PREFIX constants in this class.</p>
     *
     * @param resourcePath the String path representing the resource to obtain.
     * @return the InputStraem for the specified resource.
     * @throws IOException if there is a problem acquiring the resource at the specified path.
     */
    public static InputStream getInputStreamForPath(String resourcePath) throws IOException {

        InputStream is;
        if( resourcePath.startsWith( CLASSPATH_PREFIX ) ) {
            is = loadFromClassPath( stripPrefix( resourcePath ) );

        } else if( resourcePath.startsWith( URL_PREFIX ) ) {
            is = loadFromUrl( stripPrefix( resourcePath ) );

        } else if( resourcePath.startsWith( FILE_PREFIX ) ) {
            is = loadFromFile( stripPrefix( resourcePath ) );

        } else {
            is = loadFromFile( resourcePath );
        }

        if( is == null ) {
            throw new IOException( "Resource [" + resourcePath + "] could not be found." );
        }

        return is;
    }

    private static InputStream loadFromFile(String path) throws IOException {

        if( logger.isDebugEnabled() ) {
            logger.debug( "Opening file [" + path + "]..." );
        }

        return new FileInputStream( path );
    }

    private static InputStream loadFromUrl(String urlPath) throws IOException {

        if( logger.isDebugEnabled() ) {
            logger.debug( "Opening url [" + urlPath + "]..." );
        }

        URL url = new URL(urlPath);
        return url.openStream();
    }

    private static InputStream loadFromClassPath(String path) {
        ClassLoader classLoader = Thread.currentThread().getContextClassLoader();

        // Fall back to class loader for this class if no context class loader
        if( classLoader == null ) {
            classLoader = ResourceUtils.class.getClassLoader();
        }

        if( logger.isDebugEnabled() ) {
            logger.debug( "Opening resource from class path [" + path + "]..." );
        }

        return classLoader.getResourceAsStream( path );
    }

    private static String stripPrefix(String resourcePath) {
        return resourcePath.substring( resourcePath.indexOf( ":" ) + 1 );
    }

    public static void close(InputStream is) {
        if( is != null ) {
            try {
                is.close();
            } catch (IOException e) {
                logger.warn( "Error closing input stream.", e );
            }
        }
    }
}