Archive | April 2014

Serving static web resources in an OSGi environment

After having the persistence layer, I was thinking how to serve static resources in an OSGi based web environment. I definitely do not want to create WABs with web.xml files. This is I have come up so far:

In case we would like to offer static resources from a bundle we add the following capability to it one or more times:
Provide-Capability: static.resources
Possible attributes of the capability:
  • path: Path in the bundle where from we would like to export resources
  • filePattern: Pattern of the files that can be served. E.g.: *.gif
  • recurse: Export files from sub-directories or not. Default is true.
  • scope: Only export files from the bundle or from the imported packages as well. Possible values: local / wiring. Default is local
  • mimeConfig: Location of an optional properties file inside the bundle where file extension – metatype values are paired. E.g.: gif=image/gif
  • someAttributeKey: Optional attributes that will be listed in the OSGi service properties (see below)
A full example:
Provide-Capability: static.resources;path=/pathinbundle/;filePattern=*;recurse=true;scope=wiring;someAttributeKey=someValue

An extender picks up every bundle that contains the “static.resources” capability and registers a StaticResourceProvider OSGi service for each capability. The service properties come from the capability attributes. The functions of the StaticResourceProvider interface:

  • listFiles(String folder): Listing files and sub-directories inside the specified folder
  • getResourceAsStream(String path)
  • getMimeType(String path)
The StaticResourceProvider OSGi services can be used by the component called StaticResourceServlet. The configuration options of the component:
  • staticResourceProviders.target: OSGi filter that addresses one or more static resource provider service
  • acceptRanges: Whether range queries are accepted or not (HTTP 1.1)
  • dirAllowed: If directory listing is allowed or not
  • styleSheet: Location of a CSS static resource that could decorate directory listing
  • welcomeFileNames: Comma separeated list of welcome file names. If directory url is provided, it will be redirected to the welcome file if that exists.
  • gzFileRegex: If a file name with path matches with this optional regular expression, it will be sent unpacked, via a compressed stream if available (HTTP 1.1)
  • etags: Whether etags are allowed or not (HTTP 1.1)
  • maxCacheSize: The maximum total size of the cache or 0 for no cache.
  • maxCachedFileSize: The maximum size of a file to cache
  • maxCachedFiles: The maximum number of files to cache
  • cacheControl: If set, all static content will have this value set as the cache-controlheader
  • otherServiceProps: String array of key-value pairs that should be put into the properties of the registered OSGi service. E.g.: Putting whiteboard pattern specific properties.

The configuration properties of StaticResourceServlet component can be familiar from DefaultServlet of Jetty.

 

Update

I implemented a similar solution and it is now available at github.

The specification was changed a bit. It is more simple. As soon as I used it in a project, I will upload it to maven central.

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