Image Server
by Raul Piaggio
rpiaggio at handsoft dot com dot uy

Note from Luca The code kindly provided by Raul relies on a slightly modified version of the WURFL API. I would like to see this code compatible with WURFL evolution when it's ready, but since this utility is very useful, I prefer to publish it now. You should be able to work out the differences without problems. You can ask questions on WMLProgramming.

The ImageServer is an application for transparently multiserving images to mobile devices. For example, let's say you have the following JPG image on the server:

If you request it from a Nokia 7700, the ImageServer will automatically resize it to fit in the Nokia 7700 display and return it in JPG format:

If you request the same image from a Nokia 5700, the ImageServer will convert it to a GIF instead and resize it to an even smaller size to fit in its display:

And similarly, if you request it from a Nokia 7110, it will be converted to a WBMP (and resized):

NOTE: The aspect ratio of the image is never modified. If the aspect ratio of the image and the device differ, the image is reduced further to fit in the display.
Advanced functionality includes:

Caching

Resized/reformatted images are cached to minimize CPU work and maximize response time. If the original image changes, the cache is updated.

Remote retrieval

The original images may be in another server. In this case, ImageServer will cache the original image as well as the resized/reformatted versions. ImageServer can be instructed to check for changes in the remote image - in which case it will update it only if necessary - or just keep the cached one forever after retrieval - resulting in faster service.

• WURFL and WURFL Java Lib, which requires XOM 1.0+
• JAI 1.1.2+
• JAI Image I/O 1.1+ (beta)
• Apache commons-discovery 0.2+

UA

Allows you to simulate another device. The value should be what the device sends in its User-Agent header.
Example: http://localhost:8080/ImageServer/hello.jpg?UA=Nokia7700.

ratio

Scales the image further by the specified ratio. Useful if we want to display the image a bit smaller than the whole display (eg: ratio=0.8) or display two images side by side (eg: ratio=0.5).
Example: http://localhost:8080/ImageServer/hello.jpg?ratio=0.5
Note: By default, ImageServer scales to 0.90 so that images can be displayed in a mobile browser without the horizontal scroll bar. To override this, use ratio=1.

width and height

Override the device dimensions. Useful for example for using ImageServer to generate thumbnails in a web page. If only of these is specified, the other one is taken from the device.
Example: http://localhost:8080/ImageServer/hello.jpg?width=300&height=200

format

Override the device image format. Useful for debugging.
Example: http://localhost:8080/ImageServer/hello.jpg?format=wbmp

location

Indicates the ImageServer to retrieve the original image from another web server if not found on the local filesystem. If the protocol is ommited, then http will be used.
Example: ;br: http://localhost:8080/ImageServer/hello.jpg?location=www.imageserver.com/myimages/greetings
will look for the image hello.jpg under images and if not found will retrieve it from http://www.imageserver.com/myimages/greetings/hello.jpg and store it locally under images for future use.

Note that the remote location can be several directories deep. In this case, the path can be split between the actual request and the location parameter. However, only the directory structure specified in the actual request will be replicated when storing the image locally.

Example:
http://localhost:8080/ImageServer/greetings/hello.jpg?location=www.imageserver.com/myimages will look for the image hello.jpg under images/greetings and if not found will retrieve it from
http://www.imageserver.com/myimages/greetings/hello.jpg and store it locally under images/greetings for future use.

refresh

Used in combination with location to indicate that even if an image is stored locally, the remote server should be checked for updates (and retrieve the image again if there was an update). The image is requested from the remote server with indications to send it only if it was modified since the last retrieval. Therefore, the image is only transmitted when necessary, but the overhead of establishing a connection with the remote server is paid every time the image is requested. This parameter does not take a value, it acts by just being present.
Example: http://localhost:8080/ImageServer/greetings/hello.jpg?location=www.imageserver.com/myimages&refresh

Format priority

ImageServer tries always tries to serve first in JPG despite the original format of the image. If this is not supported by the device, it tries GIF, PNG, BMP and finally WBMP -- in that order. No other output formats are currently supported. (Input format can be any of the supported ones by JAI Image I/O).
If the device does not support any of these formats, a 404 error (resource not found) will be returned.

Native code JAI libraries

There exist native code JAI libraries for a number of platforms. Using these libraries speeds up image resizing and reformatting, but -- being native libraries -- they depend on the platform and are therefore not distributed with ImageServer.
For this reason, you will get the following message in the output when ImageServer attempts its first operation:
Error: Could not load mediaLib accelerator wrapper classes. Continuing in pure Java mode.
Occurs in: com.sun.media.jai.mlib.MediaLibAccessor
com.sun.media.jai.mlib.MediaLibLoadException
But the ImageServer will work just fine nonetheless.
To download the native libraries for your platform, plase visit the JAI page. You should download the JAI package for your platform and then copy the native libraries (.dll files for Windows or .so files for Linux, for example) in a directory where the system can find them. A good place is the lib/i386 directory under the JRE. The web server has to be restarted for this change to take effect.