Class ImageCache

java.lang.Object
org.apache.xmlgraphics.image.loader.cache.ImageCache
public class ImageCache extends 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 Details

    • log

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

    • invalidURIs

      private 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:

  • Constructor Details

    • 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 Details

    • 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(String uri, ImageSessionContext session, ImageManager manager) throws ImageException, 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
      IOException - if an I/O error occurs while loading image data

    • isInvalidURI

      public boolean isInvalidURI(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(String uri)

    • getImageInfo

      protected ImageInfo getImageInfo(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(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(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()