net.sourceforge.jnlp.cache

## Class ResourceTracker

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

-     public class ResourceTracker
      extends java.lang.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 Summary

    Constructors
    Constructor and Description
    `ResourceTracker()` Creates a resource tracker that does not prefetch resources.
    `ResourceTracker(boolean prefetch)` Creates a resource tracker.

  - ### Method Summary

    Methods
    Modifier and Type | Method and Description
    --- | ---
    `void` | `addDownloadListener(DownloadListener listener)` Adds the listener to the list of objects interested in receivind DownloadEvents.
    `void` | `addResource(java.net.URL location, Version version, DownloadOptions options, UpdatePolicy updatePolicy)` Add a resource identified by the specified location and version.
    `boolean` | `checkResource(java.net.URL location)` Returns whether a resource is available for use (ie, can be accessed with the getCacheFile method).
    `protected void` | `fireDownloadEvent(Resource resource)` Fires the download event corresponding to the resource's state.
    `long` | `getAmountRead(java.net.URL location)` Returns the number of bytes downloaded for a resource.
    `java.io.File` | `getCacheFile(java.net.URL location)` Returns a file containing the downloaded resource.
    `java.net.URL` | `getCacheURL(java.net.URL location)` Returns a URL pointing to the cached location of the resource, or the resource itself if it is a non-cacheable resource.
    `java.io.InputStream` | `getInputStream(java.net.URL location)` Returns an input stream that reads the contents of the resource.
    `long` | `getTotalSize(java.net.URL location)` Returns the number of total size in bytes of a resource, or -1 it the size is not known.
    `void` | `removeDownloadListener(DownloadListener listener)` Removes a download listener.
    `void` | `removeResource(java.net.URL location)` Removes a resource from the tracker.
    `boolean` | `startResource(java.net.URL location)` Starts loading the resource if it is not already being downloaded or already cached.
    `protected void` | `startThread()` Start a new download thread if there are not too many threads already running.
    `boolean` | `waitForResource(java.net.URL location, long timeout)` Wait for a particular resource to be downloaded and made available.
    `boolean` | `waitForResources(java.net.URL[] urls, long timeout)` Wait for a group of resources to be downloaded and made available locally.

    - ### Methods inherited from class java.lang.Object

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

- - ### Constructor Detail

    - #### 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 Detail

    - #### addResource

          public void addResource(java.net.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
        `updatePolicy` - whether to check for updates if already in cache

    - #### removeResource

          public void removeResource(java.net.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.
      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.

    - #### getCacheURL

          public java.net.URL getCacheURL(java.net.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:
        `CacheUtil.isCacheable(java.net.URL, net.sourceforge.jnlp.Version)`

    - #### getCacheFile

          public java.io.File getCacheFile(java.net.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:
        `CacheUtil.isCacheable(java.net.URL, net.sourceforge.jnlp.Version)`

    - #### getInputStream

          public java.io.InputStream getInputStream(java.net.URL location)
                                             throws java.io.IOException

      Returns an input stream that reads the contents of the resource. For non-cacheable resources, an InputStream that reads from the source location is returned. Otherwise the InputStream reads the cached resource.

      This method will block while the resource is downloaded to the cache.

      Throws:
        `java.io.IOException` - if there was an error opening the stream
        `IllegalResourceDescriptorException` - if the resource is not being tracked

    - #### waitForResources

          public boolean waitForResources(java.net.URL[] urls,
                                 long timeout)
                                   throws java.lang.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:
        `IllegalResourceDescriptorException` - if the resource is not being tracked
        `java.lang.InterruptedException`

    - #### waitForResource

          public boolean waitForResource(java.net.URL location,
                                long timeout)
                                  throws java.lang.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:
        `java.lang.InterruptedException` - if another thread interrupted the wait
        `IllegalResourceDescriptorException` - if the resource is not being tracked

    - #### getAmountRead

          public long getAmountRead(java.net.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(java.net.URL location)

      Returns whether a resource is available for use (ie, can be accessed with the getCacheFile method).
      Throws:
        `IllegalResourceDescriptorException` - if the resource is not being tracked

    - #### startResource

          public boolean startResource(java.net.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.
      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(java.net.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

    - #### startThread

          protected void startThread()

      Start a new download thread if there are not too many threads already running.

      Calls to this method should be synchronized on lock.

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