
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:
frequently
hourly
daily
(default)
weekly
- update.active=frequency
- The frequency of updates when the application is active.
Possible values are:
frequently
hourly
(default)
daily
weekly
- 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.