Package org.apache.xmlgraphics.image.loader.cache

Class ImageCache

java.lang.Object

org.apache.xmlgraphics.image.loader.cache.ImageCache

public class ImageCache
extends java.lang.Object

This class provides a cache for images. The main key into the images is the original URI the image was accessed with.

Don't use one ImageCache instance in the context of multiple base URIs because relative URIs would not work correctly anymore.

By default, the URIs of inaccessible images are remembered but these entries are discarded after 60 seconds (which causes a retry next time the same URI is requested). This allows to counteract performance loss when accessing invalid or temporarily unavailable images over slow connections.

Field Summary

Fields

Modifier and Type	Field	Description
private ImageCacheListener	cacheListener
private SoftMapCache	imageInfos
private SoftMapCache	images
private ExpirationPolicy	invalidURIExpirationPolicy
private java.util.Map	invalidURIs
private long	lastHouseKeeping
protected static org.apache.commons.logging.Log	log	logger
private static long	ONE_HOUR
private TimeStampProvider	timeStampProvider

Constructor Summary

Constructors

Constructor	Description
ImageCache()	Default constructor with default settings.
ImageCache(TimeStampProvider timeStampProvider, ExpirationPolicy invalidURIExpirationPolicy)	Constructor for customized behaviour and testing.

Method Summary

Modifier and Type	Method	Description
void	clearCache()	Clears the image cache (all ImageInfo and Image objects).
private void	considerHouseKeeping()
void	doHouseKeeping()	Triggers some house-keeping, i.e.
private void	doInvalidURIHouseKeeping()
Image	getImage(java.lang.String uri, ImageFlavor flavor)	Returns an image from the cache or null if it wasn't found.
Image	getImage(ImageInfo info, ImageFlavor flavor)	Returns an image from the cache or null if it wasn't found.
protected ImageInfo	getImageInfo(java.lang.String uri)	Returns an ImageInfo instance from the cache or null if none is found.
boolean	isInvalidURI(java.lang.String uri)	Indicates whether a URI has previously been identified as an invalid URI.
ImageInfo	needImageInfo(java.lang.String uri, ImageSessionContext session, ImageManager manager)	Returns an ImageInfo instance for a given URI.
void	putImage(Image img)	Registers an image with the cache.
protected void	putImageInfo(ImageInfo info)	Registers an ImageInfo instance with the cache.
(package private) void	registerInvalidURI(java.lang.String uri)	Registers a URI as invalid so getImageInfo can indicate that quickly with no I/O access.
private boolean	removeInvalidURIIfExpired(java.lang.String uri)
void	setCacheListener(ImageCacheListener listener)	Sets an ImageCacheListener instance so the events in the image cache can be observed.

Methods inherited from class java.lang.Object

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

Field Detail

log

protected static final org.apache.commons.logging.Log log

logger

invalidURIs

private java.util.Map invalidURIs

invalidURIExpirationPolicy

private ExpirationPolicy invalidURIExpirationPolicy

imageInfos

private SoftMapCache imageInfos

images

private SoftMapCache images

cacheListener

private ImageCacheListener cacheListener

timeStampProvider

private TimeStampProvider timeStampProvider

lastHouseKeeping

private long lastHouseKeeping

ONE_HOUR

private static final long ONE_HOUR

See Also:

Constant Field Values

Constructor Detail

ImageCache

public ImageCache()

Default constructor with default settings.

ImageCache

public ImageCache(TimeStampProvider timeStampProvider,
                  ExpirationPolicy invalidURIExpirationPolicy)

Constructor for customized behaviour and testing.

Parameters:

timeStampProvider - the time stamp provider to use

invalidURIExpirationPolicy - the expiration policy for invalid URIs

Method Detail

setCacheListener

public void setCacheListener(ImageCacheListener listener)

Sets an ImageCacheListener instance so the events in the image cache can be observed.

Parameters:

listener - the listener instance

needImageInfo

public ImageInfo needImageInfo(java.lang.String uri,
                               ImageSessionContext session,
                               ImageManager manager)
                        throws ImageException,
                               java.io.IOException

Returns an ImageInfo instance for a given URI.

Parameters:

uri - the image's URI

session - the session context

manager - the ImageManager handling the images

Returns:

the ImageInfo instance

Throws:

ImageException - if an error occurs while parsing image data

java.io.IOException - if an I/O error occurs while loading image data

isInvalidURI

public boolean isInvalidURI(java.lang.String uri)

Indicates whether a URI has previously been identified as an invalid URI.

Parameters:

uri - the image's URI

Returns:

true if the URI is invalid

removeInvalidURIIfExpired

private boolean removeInvalidURIIfExpired(java.lang.String uri)

getImageInfo

protected ImageInfo getImageInfo(java.lang.String uri)

Returns an ImageInfo instance from the cache or null if none is found.

Parameters:

uri - the image's URI

Returns:

the ImageInfo instance or null if the requested information is not in the cache

putImageInfo

protected void putImageInfo(ImageInfo info)

Registers an ImageInfo instance with the cache.

Parameters:

info - the ImageInfo instance

registerInvalidURI

void registerInvalidURI(java.lang.String uri)

Registers a URI as invalid so getImageInfo can indicate that quickly with no I/O access.

Parameters:

uri - the URI of the invalid image

getImage

public Image getImage(ImageInfo info,
                      ImageFlavor flavor)

Returns an image from the cache or null if it wasn't found.

Parameters:

info - the ImageInfo instance representing the image

flavor - the requested ImageFlavor for the image

Returns:

the requested image or null if the image is not in the cache

getImage

public Image getImage(java.lang.String uri,
                      ImageFlavor flavor)

Returns an image from the cache or null if it wasn't found.

Parameters:

uri - the image's URI

flavor - the requested ImageFlavor for the image

Returns:

the requested image or null if the image is not in the cache

putImage

public void putImage(Image img)

Registers an image with the cache.

Parameters:

img - the image

clearCache

public void clearCache()

Clears the image cache (all ImageInfo and Image objects).

considerHouseKeeping

private void considerHouseKeeping()

doHouseKeeping

public void doHouseKeeping()

Triggers some house-keeping, i.e. removes stale entries.

doInvalidURIHouseKeeping

private void doInvalidURIHouseKeeping()