Class ResourceTracker

java.lang.Object
net.sourceforge.jnlp.cache.ResourceTracker

public class ResourceTracker extends Object
This class tracks the downloading of various resources of a JNLP file to local files in the cache. It can be used to download icons, jnlp and extension files, jars, and jardiff files using the version based protocol or any file using the basic download protocol (jardiff and version not implemented yet).

The resource tracker can be configured to prefetch resources, which are downloaded in the order added to the media tracker.

Multiple threads are used to download and cache resources that are actively being waited for (blocking a caller) or those that have been started downloading by calling the startDownload method. Resources that are prefetched are downloaded one at a time and only if no other trackers have requested downloads. This allows the tracker to start downloading many items without using many system resources, but still quickly download items as needed.

  • Constructor Details

    • ResourceTracker

      public ResourceTracker()
      Creates a resource tracker that does not prefetch resources.
    • ResourceTracker

      public ResourceTracker(boolean prefetch)
      Creates a resource tracker.
      Parameters:
      prefetch - whether to download resources before requested.
  • Method Details

    • addResource

      public void addResource(URL location, Version version, DownloadOptions options, UpdatePolicy updatePolicy)
      Add a resource identified by the specified location and version. The tracker only downloads one version of a given resource per instance (ie cannot download both versions 1 and 2 of a resource in the same tracker).
      Parameters:
      location - the location of the resource
      version - the resource version
      options - options to control download
      updatePolicy - whether to check for updates if already in cache
    • removeResource

      public void removeResource(URL location)
      Removes a resource from the tracker. This method is useful to allow memory to be reclaimed, but calling this method is not required as resources are reclaimed when the tracker is collected.
      Parameters:
      location - location of resource to be removed
      Throws:
      IllegalResourceDescriptorException - if the resource is not being tracked
    • addDownloadListener

      public void addDownloadListener(DownloadListener listener)
      Adds the listener to the list of objects interested in receivind DownloadEvents.
      Parameters:
      listener - the listener to add.
    • removeDownloadListener

      public void removeDownloadListener(DownloadListener listener)
      Removes a download listener.
      Parameters:
      listener - the listener to remove.
    • fireDownloadEvent

      protected void fireDownloadEvent(Resource resource)
      Fires the download event corresponding to the resource's state. This method is typicall called by the Resource itself on each tracker that is monitoring the resource. Do not call this method with any locks because the listeners may call back to this ResourceTracker.
      Parameters:
      resource - resource on which event is fired
    • getCacheURL

      public URL getCacheURL(URL location)
      Returns a URL pointing to the cached location of the resource, or the resource itself if it is a non-cacheable resource.

      If the resource has not downloaded yet, the method will block until it has been transferred to the cache.

      Parameters:
      location - the resource location
      Returns:
      the resource, or null if it could not be downloaded
      Throws:
      IllegalResourceDescriptorException - if the resource is not being tracked
      See Also:
    • getCacheFile

      public File getCacheFile(URL location)
      Returns a file containing the downloaded resource. If the resource is non-cacheable then null is returned unless the resource is a local file (the original file is returned).

      If the resource has not downloaded yet, the method will block until it has been transferred to the cache.

      Parameters:
      location - the resource location
      Returns:
      a local file containing the resource, or null
      Throws:
      IllegalResourceDescriptorException - if the resource is not being tracked
      See Also:
    • waitForResources

      public boolean waitForResources(URL[] urls, long timeout) throws InterruptedException
      Wait for a group of resources to be downloaded and made available locally.
      Parameters:
      urls - the resources to wait for
      timeout - the time in ms to wait before returning, 0 for no timeout
      Returns:
      whether the resources downloaded before the timeout
      Throws:
      InterruptedException - if thread is interrupted
      IllegalResourceDescriptorException - if the resource is not being tracked
    • waitForResource

      public boolean waitForResource(URL location, long timeout) throws InterruptedException
      Wait for a particular resource to be downloaded and made available.
      Parameters:
      location - the resource to wait for
      timeout - the timeout, or 0 to wait until completed
      Returns:
      whether the resource downloaded before the timeout
      Throws:
      InterruptedException - if another thread interrupted the wait
      IllegalResourceDescriptorException - if the resource is not being tracked
    • getAmountRead

      public long getAmountRead(URL location)
      Returns the number of bytes downloaded for a resource.
      Parameters:
      location - the resource location
      Returns:
      the number of bytes transferred
      Throws:
      IllegalResourceDescriptorException - if the resource is not being tracked
    • checkResource

      public boolean checkResource(URL location)
      Returns whether a resource is available for use (ie, can be accessed with the getCacheFile method).
      Parameters:
      location - the resource location
      Returns:
      resource availability
      Throws:
      IllegalResourceDescriptorException - if the resource is not being tracked
    • startResource

      public boolean startResource(URL location)
      Starts loading the resource if it is not already being downloaded or already cached. Resources started downloading using this method may download faster than those prefetched by the tracker because the tracker will only prefetch one resource at a time to conserve system resources.
      Parameters:
      location - the resource location
      Returns:
      true if the resource is already downloaded (or an error occurred)
      Throws:
      IllegalResourceDescriptorException - if the resource is not being tracked
    • getTotalSize

      public long getTotalSize(URL location)
      Returns the number of total size in bytes of a resource, or -1 it the size is not known.
      Parameters:
      location - the resource location
      Returns:
      the number of bytes, or -1
      Throws:
      IllegalResourceDescriptorException - if the resource is not being tracked
    • startDownloadThread

      protected void startDownloadThread(Resource resource)
      Start a new download thread.

      Calls to this method should be synchronized on lock.

      Parameters:
      resource - resource to be download