Package org.spdx.utility

Class DownloadCache

java.lang.Object

org.spdx.utility.DownloadCache

public final class DownloadCache
extends Object

This singleton class provides a flexible download cache for the rest of the library. If enabled, URLs that are requested using this class will have their content automatically cached locally on disk (in a directory that adheres to the XDG Base Directory Specification - ...), and any subsequent requests will be served out of that cache. Cache entries will also be automatically checked every so often for staleness using HTTP ETag requests (which are more efficient than full HTTP requests). The interval between such checks is configurable (and can even be turned off, which makes every download request re-check the URL for staleness).

The cache is configured via these Configuration options: * org.spdx.storage.listedlicense.enableCache: Controls whether the cache is enabled or not. Defaults to false i.e. the cache is disabled. * org.spdx.storage.listedlicense.cacheCheckIntervalSecs: How many seconds should the cache wait between issuing ETag requests to determine whether cached content is stale? Defaults to 86,400 seconds (24 hours).

Method Summary

Modifier and Type	Method	Description
static DownloadCache	getInstance()
InputStream	getUrlInputStream(URL url)
InputStream	getUrlInputStream(URL url, boolean restrictRedirects)
void	resetCache()	Resets (deletes) the local cache

Methods inherited from class java.lang.Object

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

Method Detail

getInstance

public static DownloadCache getInstance()

Returns:

The singleton instance of the DownloadCache class.

resetCache

public void resetCache()
                throws IOException

Resets (deletes) the local cache

Throws:

IOException - on IO error

getUrlInputStream

public InputStream getUrlInputStream(URL url)
                              throws IOException

Parameters:

url - The URL to get an input stream for. Note that redirects issued by this url are restricted to known SPDX hosts. Redirects to other hosts will cause an IOException to be thrown.

Returns:

An InputStream for url, or null if url is null. Note that this InputStream may be of different concrete types, depending on whether the content is being served out of cache or not.

Throws:

IOException - When an IO error of some kind occurs.

getUrlInputStream

public InputStream getUrlInputStream(URL url,
                                     boolean restrictRedirects)
                              throws IOException

Parameters:

url - The URL to get an input stream for.

restrictRedirects - A flag that controls whether redirects returned by url are restricted to known SPDX hosts or not. Defaults to true. USE EXTREME CAUTION WHEN TURNING THIS OFF!

Returns:

An InputStream for url, or null if url is null. Note that this InputStream may be of different concrete types, depending on whether the content is being served out of cache or not.

Throws:

IOException - When an IO error of some kind occurs.