/* 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 java.net;
import java.io.IOException;
import java.util.List;
import java.util.Map;
/**
* This class is an implementation of {@code URLConnection} caches intended
* primarily for the according stream handler implementations.
* <p>
* The system's default cache can be registered by invoking the method {@code
* setDefault(ResponseCache)} and be retrieved by invoking the method {@code
* getDefault()}. If {@code URLConnection#useCaches} is set, {@code
* URLConnection} class will use {@code ResponseCache} to store and get
* resources.
* <p>
* Whether the resource is cached depends on the implementation of {@code
* ResponseCache}. If so, a {@code CacheResponse} is returned from which the
* stream handler reads. If the stream handler fails to get a resource from the
* cache, it must get the resource from its original location.
* <p>
* To write to the cache, the protocol handlers call {@code put()}, upon which a
* {@code CacheRequest} is supplied to which the resources are written.
*
* @see #put(URI, URLConnection)
* @see CacheRequest
* @see CacheResponse
* @see URLConnection
* @see URLStreamHandler
*/
public abstract class ResponseCache {
/*
* _defaultResponseCache is used to store default response cache.
*/
private static ResponseCache _defaultResponseCache = null;
/*
* "getResponseCache" permission. getDefault method requires this
* permission.
*/
private static NetPermission getResponseCachepermission = new NetPermission(
"getResponseCache"); //$NON-NLS-1$
/*
* "setResponseCache" permission. setDefault method requires this
* permission.
*/
private static NetPermission setResponseCachepermission = new NetPermission(
"setResponseCache"); //$NON-NLS-1$
/*
* check getResponseCache permission. getDefault method requires
* "getResponseCache" permission if a security manager is installed.
*/
private static void checkGetResponseCachePermission() {
SecurityManager sm = System.getSecurityManager();
if (null != sm) {
sm.checkPermission(getResponseCachepermission);
}
}
/*
* check setResponseCache permission. setDefault method requires
* "setResponseCache" permission if a security manager is installed.
*/
private static void checkSetResponseCachePermission() {
SecurityManager sm = System.getSecurityManager();
if (null != sm) {
sm.checkPermission(setResponseCachepermission);
}
}
/**
* Creates a new instance of this class.
*/
public ResponseCache() {
super();
}
/**
* Gets the default response cache of the system.
*
* @return the default {@code ResponseCache}.
* @throws SecurityException
* if a security manager is installed but it doesn't have the
* {@code NetPermission("getResponseCache")}.
*/
public static ResponseCache getDefault() {
checkGetResponseCachePermission();
return _defaultResponseCache;
}
/**
* Sets the default response cache of the system. Removes the system's
* default {@code ResponseCache} if the parameter {@code responseCache} is
* set to {@code null}. This setting may be ignored by some non-standard
* protocols.
*
* @param responseCache
* the {@code ResponseCache} instance to set as default or
* {@code null} to remove the current default {@code
* ResponseCache}.
* @throws SecurityException
* if a security manager is installed but it doesn't have the
* {@code NetPermission("setResponseCache")}.
*/
public static void setDefault(ResponseCache responseCache) {
checkSetResponseCachePermission();
_defaultResponseCache = responseCache;
}
/**
* Gets the cached response according to the requesting URI, method and
* headers.
*
* @param uri
* the requesting URI.
* @param rqstMethod
* the requesting method.
* @param rqstHeaders
* a map of requesting headers.
* @return the {@code CacheResponse} object if the request is available in the cache
* or {@code null} otherwise.
* @throws IOException
* if an I/O error occurs while getting the cached data.
* @throws IllegalArgumentException
* if any one of the parameters is set to {@code null}.
*/
public abstract CacheResponse get(URI uri, String rqstMethod,
Map<String, List<String>> rqstHeaders) throws IOException;
/**
* Allows the protocol handler to cache data after retrieving resources. The
* {@code ResponseCache} decides whether the resource data should be cached
* or not. If so, this method returns a {@code CacheRequest} with a {@code
* WriteableByteChannel} to put the resource data down. Otherwise, this
* method returns {@code null}.
*
* @param uri
* the reference to the requested resource.
* @param conn
* the connection to fetch the response.
* @return a CacheRequest object with a WriteableByteChannel if the resource
* has to be cached, {@code null} otherwise.
* @throws IOException
* if an I/O error occurs while adding the resource.
* @throws IllegalArgumentException
* if any one of the parameters is set to {@code null}.
*/
public abstract CacheRequest put(URI uri, URLConnection conn)
throws IOException;
}