ResponseCache

public abstract class ResponseCache extends Object

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

Public Constructor Summary

Public Method Summary

abstract CacheResponse
get(URI uri, String rqstMethod, Map<String, List<String>> rqstHeaders)
Retrieve the cached response based on the requesting uri, request method and request headers.
synchronized static ResponseCache
getDefault()
Gets the system-wide response cache.
abstract CacheRequest
put(URI uri, URLConnection conn)
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.
synchronized static void
setDefault(ResponseCache responseCache)
Sets (or unsets) the system-wide cache.

Inherited Method Summary

Public Constructors

public ResponseCache ()

Public Methods

public abstract CacheResponse get (URI uri, String rqstMethod, Map<String, List<String>> rqstHeaders)

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.

Parameters
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
Returns
  • a CacheResponse instance if available from cache, or null otherwise
Throws
IOException if an I/O error occurs
IllegalArgumentException if any one of the arguments is null

public static synchronized ResponseCache getDefault ()

Gets the system-wide response cache.

Returns
  • the system-wide ResponseCache
Throws
SecurityException If a security manager has been installed and it denies NetPermission("getResponseCache")

public abstract CacheRequest put (URI uri, URLConnection conn)

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.

Parameters
uri a URI used to reference the requested network resource
conn - a URLConnection instance that is used to fetch the response to be cached
Returns
  • a 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
IllegalArgumentException if any one of the arguments is null

public static synchronized void setDefault (ResponseCache responseCache)

Sets (or unsets) the system-wide cache. Note: non-standard procotol handlers may ignore this setting.

Parameters
responseCache The response cache, or null to unset the cache.
Throws
SecurityException If a security manager has been installed and it denies NetPermission("setResponseCache")
See Also