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Public API for the Apache MyFaces Trinidad project
There is a newer version: 2.2.1
/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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.myfaces.trinidad.resource;

import java.io.IOException;

import java.net.URL;
import java.net.URLConnection;


/**
 * Base class for resource loaders.  Resource loaders can lookup resources
 * as URLs from arbitrary locations, including JAR files.
 *
 */
public class ResourceLoader
{
  /**
   * Returns the shared resource loader that always returns null.
   *
   * @return null for any resource path
   */
  public static ResourceLoader getNullResourceLoader()
  {
    return _NULL_RESOURCE_LOADER;
  }

  /**
   * Finds the resource with the given name.  A resource is some data
   * (images, audio, text, etc) that can be accessed by class code in a way
   * that is independent of the location of the code.
   *
   *  The name of a resource is a '/'-separated path name that
   * identifies the resource.
   *
   * 
 This method will first search the this resource loader for the
   * resource.  That failing, this method will invoke
   * {@link #findResource(String)} to on the parent resource loader to
   * find the resource.  
   *
   * @param  name  the resource name
   *
   * @return  A URL object for reading the resource, or
   *          null if the resource could not be found or the invoker
   *          doesn't have adequate privileges to get the resource.
   */
  public URL getResource(
    String name
    ) throws IOException
  {
    URL url = findResource(name);

    if (url == null && _parent != null)
    {
      url = _parent.getResource(name);
    }

    return url;
  }

  /**
   * Returns whether a resource is cachable.
   * @return
   */
  public boolean isCachable()
  {
    return _parent == null || _parent.isCachable();
  }

  @Override public String toString()
  {
    StringBuilder result = new StringBuilder();
    result.append(super.toString());
    
    if (_parent != null)
    {
      result.append("("+_parent.toString()+")");
    }
    return result.toString();
  }

  /**
   * Finds the resource with the given name. Resource loader implementations
   * should override this method to specify where to find resources.  
   *
   * @param  name
   *         The resource name
   *
   * @return  A URL object for reading the resource, or
   *          null if the resource could not be found
   */
  protected URL findResource(
    String name
    ) throws IOException
  {
    return null;
  }

  /**
   * Called by the {@link org.apache.myfaces.trinidad.webapp.ResourceServlet} to get the content type for
   * the given connection.
   *
   * @param loader the loader that provided the URL for the URL connection
   * @param conn the URL connection
   * @return the content type for this URL connection
   */
  public static String getContentType(
    ResourceLoader loader,
    URLConnection  conn)
  {
    return loader.getContentType(conn);
  }

  /**
   * Returns the content type of this URL connection.
   * @return the content type
   */
  protected String getContentType(
    URLConnection conn)
  {
    return conn.getContentType();
  }

  /**
   * Returns the parent resource loader, or null if this is a root
   * resource loader.
   *
   * @return  the parent resource loader
   */
  protected ResourceLoader getParent()
  {
    return _parent;
  }

  /**
   * Constructs a new resource loader with specified parent resource loader.
   *
   * @param parent  the parent resource loader
   */
  protected ResourceLoader(
    ResourceLoader parent)
  {
    _parent = parent;
  }

  /**
   * Constructs a new root resource loader.
   */
  protected ResourceLoader()
  {
    this(null);
  }

  private static final ResourceLoader _NULL_RESOURCE_LOADER =
                                                      new ResourceLoader();

  private final ResourceLoader _parent;

}