com.gargoylesoftware.htmlunit

Class Cache

java.lang.Object

com.gargoylesoftware.htmlunit.Cache

All Implemented Interfaces:

Serializable

public class Cache
extends Object
implements Serializable

Simple cache implementation which caches compiled JavaScript files and parsed CSS snippets. Caching compiled JavaScript files avoids unnecessary web requests and additional compilation overhead, while caching parsed CSS snippets avoids very expensive CSS parsing.

Author:

Marc Guillemot, Daniel Gredler, Ahmed Ashour

See Also:

Serialized Form

Constructor Summary

Constructors

Constructor and Description
Cache()

Method Summary

Methods

Modifier and Type	Method and Description
void	cache(String css, org.w3c.dom.css.CSSStyleSheet styleSheet) Caches the parsed version of the specified CSS snippet.
boolean	cacheIfPossible(WebRequest request, WebResponse response, Object toCache) Caches the specified object, if the corresponding request and response objects indicate that it is cacheable.
void	clear() Clears the cache.
protected void	deleteOverflow() Truncates the cache to the maximal number of entries.
Object	getCachedObject(WebRequest request) Returns the cached object corresponding to the specified request.
WebResponse	getCachedResponse(WebRequest request) Returns the cached response corresponding to the specified request.
org.w3c.dom.css.CSSStyleSheet	getCachedStyleSheet(String css) Returns the cached parsed version of the specified CSS snippet.
protected long	getCurrentTimestamp() Gets the current time stamp.
int	getMaxSize() Returns the cache's maximum size.
int	getSize() Returns the number of entries in the cache.
protected boolean	isCacheable(WebRequest request, WebResponse response) Determines if the specified response can be cached.
protected boolean	isCacheableContent(WebResponse response) Tries to guess if the content is dynamic or not.
protected Date	parseDateHeader(WebResponse response, String headerName) Parses and returns the specified date header of the specified response.
void	setMaxSize(int maxSize) Sets the cache's maximum size.

Methods inherited from class java.lang.Object

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

Constructor Detail

Cache

public Cache()

Method Detail

cacheIfPossible

public boolean cacheIfPossible(WebRequest request,
                      WebResponse response,
                      Object toCache)

Caches the specified object, if the corresponding request and response objects indicate that it is cacheable.

Parameters:

request - the request corresponding to the specified compiled script

response - the response corresponding to the specified compiled script

toCache - the object that is to be cached, if possible (may be for instance a compiled script or simply a WebResponse)

Returns:

whether the response was cached or not

cache

public void cache(String css,
         org.w3c.dom.css.CSSStyleSheet styleSheet)

Caches the parsed version of the specified CSS snippet. We key the cache based on CSS snippets (rather than requests and responses as is done above) because a) this allows us to cache inline CSS, b) CSS is extremely expensive to parse, so we want to avoid it as much as possible, c) CSS files aren't usually nearly as large as JavaScript files, so memory bloat won't be too bad, and d) caching on requests and responses requires checking dynamicity (see isCacheableContent(WebResponse)), and headers often aren't set up correctly, disallowing caching when in fact it should be allowed.

Parameters:

css - the CSS snippet from which styleSheet is derived

styleSheet - the parsed version of css

deleteOverflow

protected void deleteOverflow()

Truncates the cache to the maximal number of entries.

isCacheable

protected boolean isCacheable(WebRequest request,
                  WebResponse response)

Determines if the specified response can be cached.

Parameters:

request - the performed request

response - the received response

Returns:

true if the response can be cached

isCacheableContent

protected boolean isCacheableContent(WebResponse response)

Tries to guess if the content is dynamic or not.

"Since origin servers do not always provide explicit expiration times, HTTP caches typically assign heuristic expiration times, employing algorithms that use other header values (such as the Last-Modified time) to estimate a plausible expiration time".

The current implementation considers as dynamic content everything except responses with a Last-Modified header with a date older than 10 minutes or with an Expires header specifying expiration in more than 10 minutes.

Parameters:

response - the response to examine

Returns:

true if the response should be considered as cacheable

See Also:

RFC 2616

getCurrentTimestamp

protected long getCurrentTimestamp()

Gets the current time stamp. As method to allow overriding it, when simulating an other time.

Returns:

the current time stamp

parseDateHeader

protected Date parseDateHeader(WebResponse response,
                   String headerName)

Parses and returns the specified date header of the specified response. This method returns null if the specified header cannot be found or cannot be parsed as a date.

Parameters:

response - the response

headerName - the header name

Returns:

the specified date header of the specified response

getCachedResponse

public WebResponse getCachedResponse(WebRequest request)

Returns the cached response corresponding to the specified request. If there is no corresponding cached object, this method returns null.

Parameters:

request - the request whose corresponding response is sought

Returns:

the cached response corresponding to the specified request if any

getCachedObject

public Object getCachedObject(WebRequest request)

Returns the cached object corresponding to the specified request. If there is no corresponding cached object, this method returns null.

Parameters:

request - the request whose corresponding cached compiled script is sought

Returns:

the cached object corresponding to the specified request if any

getCachedStyleSheet

public org.w3c.dom.css.CSSStyleSheet getCachedStyleSheet(String css)

Returns the cached parsed version of the specified CSS snippet. If there is no corresponding cached stylesheet, this method returns null.

Parameters:

css - the CSS snippet whose cached stylesheet is sought

Returns:

the cached stylesheet corresponding to the specified CSS snippet

getMaxSize

public int getMaxSize()

Returns the cache's maximum size. This is the maximum number of files that will be cached. The default is 25.

Returns:

the cache's maximum size

setMaxSize

public void setMaxSize(int maxSize)

Sets the cache's maximum size. This is the maximum number of files that will be cached. The default is 25.

Parameters:

maxSize - the cache's maximum size (must be >= 0)

getSize

public int getSize()

Returns the number of entries in the cache.

Returns:

the number of entries in the cache

clear

public void clear()

Clears the cache.