netx.jnlp.cache

Class 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.

Version:
$Revision: 1.22 $
Author:
Jon A. Maxwell (JAM) - initial author

Nested Class Summary

(package private) class
ResourceTracker.Downloader
This class downloads and initializes the queued resources.

Constructor Summary

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

Method Summary

void
addDownloadListener(DownloadListener listener)
Adds the listener to the list of objects interested in receivind DownloadEvents.
void
addResource(URL location, Version version, UpdatePolicy updatePolicy)
Add a resource identified by the specified location and version.
boolean
checkResource(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(URL location)
Returns the number of bytes downloaded for a resource.
File
getCacheFile(URL location)
Returns a file containing the downloaded resource.
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.
InputStream
getInputStream(URL location)
Returns an input stream that reads the contents of the resource.
long
getTotalSize(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(URL location)
Removes a resource from the tracker.
boolean
startResource(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(URL location, long timeout)
Wait for a particular resource to be downloaded and made available.
boolean
waitForResources(urls[] , long timeout)
Wait for a group of resources to be downloaded and made available locally.

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

addDownloadListener

public void addDownloadListener(DownloadListener listener)
Adds the listener to the list of objects interested in receivind DownloadEvents.

Parameters:

addResource

public void addResource(URL location,
                        Version version,
                        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

checkResource

public boolean checkResource(URL location)
Returns whether a resource is available for use (ie, can be accessed with the getCacheFile method).

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.

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

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

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

getInputStream

public InputStream getInputStream(URL location)
            throws 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.


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

removeDownloadListener

public void removeDownloadListener(DownloadListener listener)
Removes a download listener.

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.

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.
Returns:
true if the resource is already downloaded (or an error occurred)

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.


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

waitForResources

public boolean waitForResources(urls[] ,
                                long timeout)
            throws InterruptedException
Wait for a group of resources to be downloaded and made available locally.
Parameters:
timeout - the time in ms to wait before returning, 0 for no timeout
Returns:
whether the resources downloaded before the timeout