Module java.base
Package java.net

# Class ResponseCache

java.lang.Object
java.net.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

Since:
  1.5
External Specifications
  - RFC 2616: Hypertext Transfer Protocol -- HTTP/1.1

## Constructor Summary

Constructors
Constructor
Description
`ResponseCache()`
Constructor for subclasses to call.

## Method Summary

Modifier and Type
Method
Description
`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.
`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.
`static void`
`setDefault(ResponseCache responseCache)`
Sets (or unsets) the system-wide cache.

### Methods declared in class java.lang.Object

`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

## Constructor Details

### ResponseCache

public ResponseCache()
Constructor for subclasses to call.

## Method Details

### getDefault

public static 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")`
Since:
  1.5
See Also:
  - `setDefault(ResponseCache)`

### setDefault

public static void setDefault(ResponseCache responseCache)
Sets (or unsets) the system-wide cache. Note: non-standard protocol 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")`
Since:
  1.5
See Also:
  - `getDefault()`

### get

public abstract CacheResponse get(URI uri, String rqstMethod, Map<String,List<String>> rqstHeaders) throws IOException
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
See Also:
  - `URLConnection.setUseCaches(boolean)`
  - `URLConnection.getUseCaches()`
  - `URLConnection.setDefaultUseCaches(boolean)`
  - `URLConnection.getDefaultUseCaches()`

### put

public abstract CacheRequest put(URI uri, URLConnection conn) 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.

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