Channel Administration

The current release comes with a set of preconfigured example channels that you can use these as examples and to test the transmitter. The example channels can be found in the channels directory.

Once the transmitter is running and has some channels you can subscribe to channels using the Software Tuner application (which you have to get separately).


Channel Directories

Channels are just directories with code and data. Developers create channels locally, and then publish them to a transmitter using the publish command. In order for the tuner to run a channel, the channel must specify some configuration parameters.


Channel Configuration Parameters

Each channel directory contains a properties.txt file which specifies the channel's configuration parameters. Here are the currently recognized configuration parameters for a channel:
type=applet|application|presentation|html
The type of application.

main=classname
The name of the class to run when this channel is executed. For applets this should be marimba.channel.AppletViewer. You need to specify this property if you want your application to run at all. The CLASSPATH of the application will include the channel's directory which means that top level classes can be located in the top level channel directory.

codebase=pathname This allows you to alter the default CLASSPATH of the application. The specified pathname is relative to the channels directory.

name=channelname
The symbolic name of the channel. This is the name that will appear in the list of subscribed channels.

update.inactive=frequency
The frequency of updates when the application is inactive.
Possible values are:

update.active=frequency
The frequency of updates when the application is active.
Possible values are:

http.access=true
Setting this property to true indicates that this channel contains HTML files and is accessible through an HTTP proxy. Once subscribed to this channel the tuner will function as a proxy so that the user can browse the channel without requiring network access.

copyright=text
Short (one line) copyright notice.

author=name or email
The name or email address of the author of the channel.

admin=name or email
The name or email address of the administrator of the channel.

description=text
A short (one paragraph) description of the channel.

icon=image file name
The file name of a icon image for the channel (64x64 pixels).

windows.icon=image file name
The file name of a icon which should be used on windows platforms (64x64 pixels).


Creating a Channel from an Existing Applet

It takes very little effort to turn most existing applets into channels. Simply create a channel directory locally and copy the applet (with all its classes and other resources) into this directory.

Now create a properties.txt file in the channel directory. You must specify the main attribute to be marimba.channel.AppletViewer. In addition to the main attribute you should also specify any additional applet attributes (such as width and height) in the properties file.

Use the publish command to make your channel available on a transmitter.

An example of an applet that was turned into a channel can be found in the Crossword applet. The properties.txt file of this channel contains the parameters needed to start this applet.


Creating a Channel from a Presentation

It is very easy to create a channel from a presentation which you create with Bongo. Save the presentation together with all its resources in the channel directory. Now specify a property file that specifies a main attribute to be marimba.channel.ApplicationPlayerFrame. You also need to specify a presentation property to specify the presentation file.

Use the publish command to make your channel available on a transmitter.


Creating a Channel from a Web-Site

It is possible to create a channel from a Web-site. This is done by adding a properties.txt file to the Web-site and setting the http.access property to true.

The channel can then be accessed using the tuner application as a proxy for the user's browser. A channel can contain both an application as well as HTML pages.

Use the publish command to make your channel available on a transmitter.

An example of such a channel is the html-sample channel. The properties.txt file of this channel sets the http.access property to true. Note that the example contains an HTML page which contains a Java applet.


Direct Network Connections

Most applets will work in the tuner without modification. However, some applets that make direct network connections using URLs or sockets may not work without some minor changes. The reason is that the base URL of the applet uses the tuner protocol instead of the http protocol. The tuner protocol accesses files directly from the tuner's cache instead of fetching them over the network using HTTP. This is usually much faster.

Applets that rely on making direct network connections may have to be changed so that they change the base URL protocol back to http before using the HTTP in order to get the same semantics.


Updating a Channel

The Headlines channel is an example of a application that can deal with updates while the application is runing. To demonstrate this feature you must run the transmitter on your machine and subscribe to the Headlines channel. Once you are subscribed you will see a scrolling message on a textured background.

You can change the message on the server and have it appear in all the active Headlines application on the client side. The first step is to edit the file data in your Headlines development directory and change the message it contains. You then have to publish your channel on the running transmitter by running the publish command.

    prompt> cd Headlines
    prompt> edit data       (edit the data file)
    prompt> publish .

The Headlines channel is configured to be update once per minute while it is active. This means that in approximately a minute the new message will automatically appear. If a minute is too long to wait for, you can also select update from the menu in the tuner (make sure the Headlines channel is selected).


Launching a Channel from a Browser

The transmitter will automatically respond with a channel listing of all the available channels when you visit it with a Web browser with an empty file name. You can launch channels by clicking on the individual channel links.

You can add links to individual channels from your own home page. Refer to the HTML listing of the automatically generated channel listing on what URL you should use.

Note that the user must have correctly configured the mailcap and mime type files for the browser that is being used. This is normally automatically taken care of in the installation phase of the Software Tuner. See the Tuner installation instructions for more detail.