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	/*
	* 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 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 java.net.URLConnection#setUseCaches(boolean)
	* @see java.net.URLConnection#getUseCaches()
	* @see java.net.URLConnection#setDefaultUseCaches(boolean)
	* @see java.net.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;
	}

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