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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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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:
   
  • store resource data which has been retrieved from an
           external source into the cache
    • 
        
  • try to fetch a requested resource that may have been
           stored in the cache
    • 
   

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 RFC 2616: Hypertext
Transfer Protocol -- HTTP/1.1

Author:Yingxian Wang
Since:1.5
/**
 * 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 {

    
Constructor for subclasses to call.

/**
     * Constructor for subclasses to call.
     */
    public ResponseCache() {}

    
The system wide cache that provides access to a url
caching mechanism.

See Also:
/**
     * 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 NetPermission("getResponseCache")
See Also:
Returns:the system-wide ResponseCache
Since:1.5
/**
     * 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 static synchronized 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 protocol handlers may ignore this setting.

Params:
  • responseCache – The response cache, or null to unset the cache.
Throws:
See Also:
Since:1.5
/**
     * Sets (or unsets) the system-wide cache.
     *
     * Note: non-standard protocol 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 static synchronized 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.

Params:
  • uri – a URI used to reference the requested network resource
  • rqstMethod – a String representing the request method
  • rqstHeaders – - a Map from request header
           field names to lists of field values representing
           the current request headers
Throws:
See Also:
Returns:a CacheResponse instance if available from cache, or null otherwise
/**
     * 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.

Params:
  • uri – a URI used to reference the requested network resource
  • conn – - a URLConnection instance that is used to fetch
           the response to be cached
Throws:
Returns:a CacheRequest for recording the response to be cached. Null return indicates that the caller does not intend to cache the response.
/**
     * 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;
}