In some applications a full-fledged bit-mapped graphical user interface is
not feasible or appropriate. If you find yourself in one of the following situations,
Charva may be your solution:
- You may be using
ruggedized mobile computers that only have an ASCII display.
- You may need to develop an administrative interface for a remote server or firewall, and
you don't have enough bandwidth for X Windows or
the VNC protocol.
- You may have an existing application that is based on a large number of text terminals
(distributed throughout the country or the world), and you want to avoid or postpone the expense
and disruption of
(a) replacing them all with PCs or graphical workstations, and
(b) retraining all the users in the use of
a new graphical application interface.
CHARVA is a Java framework for presenting a "graphical" user interface,
composed of elements such as windows, dialogs, menus, textfields and buttons,
on a traditional character-cell ASCII terminal. It has an API based on
that of "Swing" (a.k.a. the Java Foundation Classes). Programmers familiar
with AWT and Swing will find programming CHARVA straightforward.
User interfaces can be designed on a WYSIWYG IDE,
and then easily converted to CHARVA merely by changing the "import" statements
to import the "charva.awt and "charvax.swing" packages instead of the
standard "java.awt" and "javax.swing" packages.
CHARVA was designed to bring the power and flexibility of Java to applications
on Linux/Unix systems (and has also been ported to MS Windows). ASCII
terminal-based applications can now benefit from Java features such as
object orientation, multithreading, automatic garbage-collection, and a
vast range of libraries such as:
- socket and HTTP networking using Java 2 Standard Edition
- SSL and HTTPS encryption using Java Secure Socket Extension
- asynchronous messaging using Java Message Service
- database access using Java Database Connectivity
- mail access using
- XML parsing and generation using Xerces
- and many more....
(click here for a list)
Here are some benefits of CHARVA:
- The Total Cost of Ownership (TCO) of an ASCII terminal or thin-client is considerably
lower than that of a desktop PC. TCO refers to the total cost of acquiring,
deploying and maintaining equipment; in the case of a PC running MS-Windows and
configured as a GUI workstation, the ongoing maintenance cost (including
protecting the PC against viruses!) is considerable. For many applications
such as Point-of-Sale and Point-of-Service (POS), a graphical workstation
is complete overkill. ASCII terminals are still widely used for POS
applications, at least in the developing world.
- CHARVA addresses the headache of software distribution in a large network.
You can use a single Linux computer to serve many dozens of ASCII terminals / terminal-emulators,
each running its own instance of the same application. The Linux computer
can handle the user interface logic and communicate (using standard protocols
such as HTTP, HTTPS, RMI or SOAP) via a network (LAN or WAN) with an Application
Server, which handles the business logic.
So instead of having to download a new version of the application to each
workstation every time the application changes, you download only one copy of the
new version (to the Linux front-end server).
- The memory footprint and CPU usage of the CHARVA framework are
considerably less than those of Swing. Provided you are using a terminal
with a high bit-rate (or a PC-based terminal-emulator such as
PuTTY on a LAN), the response
of CHARVA is much crisper than that of Swing. A single Linux
server can support many dozen ASCII terminals running CHARVA-based applications.
- CHARVA uses a standard, flexible and powerful API which is already familiar
to most Java programmers, thus enabling you to be productive without any
delay. And because CHARVA applications are less complex than browser-based applications with
equivalent functionality, they are faster to develop and cost less to maintain.
- CHARVA is licensed with the
GNU Lesser General Public License,
which essentially means that it is free for commercial and non-commercial use.
CHARVA is composed of two components:
- A library of Java classes that implement the various "graphical widgets"
- A dynamically-loaded shared library, written in C.
CHARVA is not a "Pure Java" package; the Java classes use the
Interface (JNI) to call screen-handling functions provided by the shared
"libTerminal.so" library, which is linked with the
library. Porting CHARVA to a different platform involves recompiling the C
source code for the libTerminal.so shared library. GNU ncurses is supported
on dozens of Unix flavors besides Linux; CHARVA should be able to run on
any platform that supports both Java and ncurses.
Although developed primarily on Linux, CHARVA has also been ported to the following operating systems
(OS-specific Makefiles are provided in the download zipfile).
Many developers around the world have used CHARVA in their
applications, and have reported that it is reliable and stable.