content: /*
   * Copyright (c) 2003, 2013, Oracle and/or its affiliates. All rights reserved.
   * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   *
   * This code is free software; you can redistribute it and/or modify it
   * under the terms of the GNU General Public License version 2 only, as
   * published by the Free Software Foundation.  Oracle designates this
   * particular file as subject to the "Classpath" exception as provided
   * by Oracle in the LICENSE file that accompanied this code.
   *
   * This code is distributed in the hope that it will be useful, but WITHOUT
   * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
   * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
   * version 2 for more details (a copy is included in the LICENSE file that
   * accompanied this code).
   *
   * You should have received a copy of the GNU General Public License version
   * 2 along with this work; if not, write to the Free Software Foundation,
   * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   *
   * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
   * or visit www.oracle.com if you need additional information or have any
   * questions.
   */
  
  package java.net;
  
  import java.io.IOException;
  import java.util.Map;
  import java.util.List;
  import sun.security.util.SecurityConstants;
  
  /**
   * Represents implementations of URLConnection caches. An instance of
   * such a class can be registered with the system by doing
   * ResponseCache.setDefault(ResponseCache), and the system will call
   * this object in order to:
   *
   *    <ul><li>store resource data which has been retrieved from an
   *            external source into the cache</li>
   *         <li>try to fetch a requested resource that may have been
   *            stored in the cache</li>
   *    </ul>
   *
   * The ResponseCache implementation decides which resources
   * should be cached, and for how long they should be cached. If a
   * request resource cannot be retrieved from the cache, then the
   * protocol handlers will fetch the resource from its original
   * location.
   *
   * The settings for URLConnection#useCaches controls whether the
   * protocol is allowed to use a cached response.
   *
   * For more information on HTTP caching, see <a
   * href="http://www.ietf.org/rfc/rfc2616.txt"><i>RFC&nbsp;2616: Hypertext
   * Transfer Protocol -- HTTP/1.1</i></a>
   *
   * @author Yingxian Wang
   * @since 1.5
   */
  public abstract class ResponseCache {
  
      /**
       * The system wide cache that provides access to a url
       * caching mechanism.
       *
       * @see #setDefault(ResponseCache)
       * @see #getDefault()
       */
      private static ResponseCache theResponseCache;
  
      /**
       * Gets the system-wide response cache.
       *
       * @throws  SecurityException
       *          If a security manager has been installed and it denies
       * {@link NetPermission}{@code ("getResponseCache")}
       *
       * @see #setDefault(ResponseCache)
       * @return the system-wide {@code ResponseCache}
       * @since 1.5
       */
      public synchronized  static ResponseCache getDefault() {
          SecurityManager sm = System.getSecurityManager();
          if (sm != null) {
              sm.checkPermission(SecurityConstants.GET_RESPONSECACHE_PERMISSION);
          }
          return theResponseCache;
      }
  
      /**
       * Sets (or unsets) the system-wide cache.
       *
       * Note: non-standard procotol handlers may ignore this setting.
       *
       * @param responseCache The response cache, or
       *          {@code null} to unset the cache.
       *
       * @throws  SecurityException
       *          If a security manager has been installed and it denies
       * {@link NetPermission}{@code ("setResponseCache")}
       *
       * @see #getDefault()
       * @since 1.5
       */
      public synchronized static void setDefault(ResponseCache responseCache) {
          SecurityManager sm = System.getSecurityManager();
          if (sm != null) {
              sm.checkPermission(SecurityConstants.SET_RESPONSECACHE_PERMISSION);
          }
          theResponseCache = responseCache;
      }
  
      /**
       * Retrieve the cached response based on the requesting uri,
       * request method and request headers. Typically this method is
       * called by the protocol handler before it sends out the request
       * to get the network resource. If a cached response is returned,
       * that resource is used instead.
       *
       * @param uri a {@code URI} used to reference the requested
       *            network resource
       * @param rqstMethod a {@code String} representing the request
       *            method
       * @param rqstHeaders - a Map from request header
       *            field names to lists of field values representing
       *            the current request headers
       * @return a {@code CacheResponse} instance if available
       *          from cache, or null otherwise
       * @throws  IOException if an I/O error occurs
       * @throws  IllegalArgumentException if any one of the arguments is null
       *
       * @see     URLConnection#setUseCaches(boolean)
       * @see     URLConnection#getUseCaches()
       * @see     URLConnection#setDefaultUseCaches(boolean)
       * @see     URLConnection#getDefaultUseCaches()
       */
      public abstract CacheResponse
          get(URI uri, String rqstMethod, Map<String, List<String>> rqstHeaders)
          throws IOException;
  
      /**
       * The protocol handler calls this method after a resource has
       * been retrieved, and the ResponseCache must decide whether or
       * not to store the resource in its cache. If the resource is to
       * be cached, then put() must return a CacheRequest object which
       * contains an OutputStream that the protocol handler will
       * use to write the resource into the cache. If the resource is
       * not to be cached, then put must return null.
       *
       * @param uri a {@code URI} used to reference the requested
       *            network resource
       * @param conn - a URLConnection instance that is used to fetch
       *            the response to be cached
       * @return a {@code CacheRequest} for recording the
       *            response to be cached. Null return indicates that
       *            the caller does not intend to cache the response.
       * @throws IOException if an I/O error occurs
       * @throws IllegalArgumentException if any one of the arguments is
       *            null
       */
      public abstract CacheRequest put(URI uri, URLConnection conn)  throws IOException;
  }
  