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/*
Copyright (c) 2007 Health Market Science, Inc.

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 com.healthmarketscience.common.util.resource;

import com.healthmarketscience.common.util.URLProtocolHandlerUtil;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.net.URL;
import java.net.URLConnection;
import java.net.URLStreamHandler;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

/**
 * Classpath resource URLHandler provides easy access to resources via the
 * classloader system. URL's take the form of  *  resource:/com/company/path/to/file.txt
 * 
 *
 * @author Tim McCune
 * @see java.net.URL
 */
public class Handler extends URLStreamHandler {

  private static final Log LOG = LogFactory.getLog(Handler.class);
  private static final String PROTOCOL = "resource";
  
  static {
    try {
      URLProtocolHandlerUtil.registerProtocolHandler(PROTOCOL, new Handler());
    } catch (Error e) {
      LOG.warn("Can't register protocol handler", e);
      throw e;
    } catch (RuntimeException e) {
      LOG.warn("Can't register protocol handler", e);
      throw e;
    }
  }

  /** 
   * Classes that need to handle resource-style URLs can call this message to
   * ensure that this class is initialized.
   */
  public static void init() {
    // Don't do anything.  This method is just called to initialize class.
  }
  
  /**
   * Parse a string into a URL object. Host and port are not changed. Only
   * the file attribute is changed.
   */
  @Override
  protected void parseURL(URL u,
  String spec,
  int start,
  int limit) {

    // Args to setURL are:
    //   URL u,
    //   String protocol,
    //   String host,
    //   int port,
    //   String authority,
    //   String userInfo,
    //   String file,
    //   String query,
    //   String ref
    super.setURL(u, PROTOCOL, null, -1, null, null, 
    spec.substring(start, limit), null, null);
    
  }
  
  
  /**
   * Opens a connection to the object referenced by the URL argument.
   */
  @Override
  protected URLConnection openConnection(URL u)
  throws IOException {
    
    URL res = convertToSystemURL(u);
    
    if (res == null) {
      throw new FileNotFoundException(u + " not found");
    }
    return res.openConnection();
  }
  
  
  public URL convertToSystemURL(URL u) {
    String path = u.getFile();
    while (path.charAt(0) == '/') {
      path = path.substring(1);
      // skip preceding slashes
    }
    
    ClassLoader loader = Thread.currentThread().getContextClassLoader();
    URL res = ((loader != null) ? loader.getResource(path) : null);
    
    if (res == null) {
      res = u.getClass().getResource( path );
    }
    if (res == null) {
      res = ClassLoader.getSystemResource(path);
    }
    while (res == null && loader != null) {
      loader = loader.getParent();
      if (loader != null) {
        res = loader.getResource(path);
      }
    }
    
    return res;
  }
  
}