org.apache.tapestry.asset
Class AssetExternalizer

java.lang.Object
  org.apache.tapestry.asset.AssetExternalizer

public class AssetExternalizer
extends Object

Responsible for copying assets from the classpath to an external directory that is visible to the web server. The externalizer is stored inside the ServletContext as a named attribute.

The externalizer uses the name org.apache.tapestry.AssetExternalizer.application name . It configures itself using two additional properties (searching in IEngine.getPropertySource().

Parameter	Description
org.apache.tapestry.asset.dir	The directory to which assets will be copied.
org.apache.tapestry.asset.URL	The corresponding URL for the asset directory.

If either of these parameters is null, then no externalization occurs. Private assets will still be available, just less efficiently, as the application will be invoked via its servlet and, ultimately, the AssetService will need to retrieve the asset.

Assets maintain thier directory structure when copied. For example, an asset with a resource path of /com/skunkworx/Banner.gif would be copied to the file system as dir/com/skunkworx/Banner.gif and would have a URL of URL/com/skunkworx/Banner.gif.

The externalizer will create any directories as needed.

The externalizer will not overwrite existing files. When a new version of the application is deployed with changed assets, there are two deployment stategies:

• Delete the existing asset directory and allow the externalizer to recreate and repopulate it.
• Change the asset directory and URL, allowing the old and new assets to exist side-by-side.

When using the second approach, it is best to use a directory that has a version number in it, for example, D:/inetpub/assets/0 mapped to the URL /assets/0. When a new version of the application is deployed, the trailing version number is incremented from 0 to 1.

Version:

$Id: AssetExternalizer.java 243791 2004-02-19 17:38:13Z hlship $

Author:

Howard Lewis Ship

Constructor Summary

protected

AssetExternalizer(IRequestCycle cycle)

Method Summary

protected void	externalize(String resourcePath)
static AssetExternalizer	get(IRequestCycle cycle) Gets the externalizer singleton for the application.
String	getURL(String resourcePath) Gets the URL to a private resource.

Methods inherited from class java.lang.Object

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

Constructor Detail

AssetExternalizer

protected AssetExternalizer(IRequestCycle cycle)

Method Detail

externalize

protected void externalize(String resourcePath)
                    throws IOException

Throws:

IOException

get

public static AssetExternalizer get(IRequestCycle cycle)

Gets the externalizer singleton for the application. If it does not already exist, it is created and stored into the ServletContext.

Each Tapestry application within a single ServletContext will have its own externalizer; they are differentiated by the application name.

See Also:

ApplicationSpecification.getName()

getURL

public String getURL(String resourcePath)

Gets the URL to a private resource. If the resource was previously copied out of the classpath, the previously generated URL is returned.

If the asset directory and URL are not configured, then returns null.

Otherwise, the asset is copied out to the asset directory, the URL is constructed (and recorded for later) and the URL is returned.

This method is not explicitly synchronized but should work multi-threaded. It synchronizes on the internal Map used to map resource paths to URLs.

Parameters:

resourcePath - The full path of the resource within the classpath. This is expected to include a leading slash. For example: /com/skunkworx/Banner.gif.