Features of Jexer

  

When building terminal applications, developers often face several challenges such as managing screen rendering, handling keyboard input, organizing layouts, and maintaining responsive interactions. Implementing these features manually requires significant effort and deep knowledge of terminal behavior.

 

This is where Jexer becomes extremely useful. Jexer provides a comprehensive framework that simplifies terminal application development by offering a rich set of built-in features. These features allow developers to create structured, interactive, and visually organized terminal applications without dealing with low-level terminal operations.

 

In this section, we will explore the core features of Jexer and see how each capability helps developers build sophisticated Text User Interface (TUI) applications.

 

1. Window Manager

One of the most powerful features of Jexer is its built-in window manager.

 

Instead of displaying all information on a single screen, Jexer allows applications to create independent windows inside the terminal. These windows behave similarly to desktop application windows and can contain their own components and content.

 

The window manager is responsible for:

 

·      creating and managing windows

·      controlling focus between windows

·      handling window movement and resizing

·      rendering overlapping windows correctly

 

This feature makes it possible to design complex applications that organize different tasks in separate windows.

 

For example, a monitoring application might contain:

 

·      a system metrics window

·      a log viewer window

·      a configuration window

 

Each window operates independently while sharing the same terminal screen.

 

2. Multiple Windows

Building on top of the window manager, Jexer allows applications to display multiple windows simultaneously.

 

Users can interact with different windows in the same application, switch focus between them, and manage their layout.

 

This enables developers to build interfaces similar to desktop environments where different tasks are organized into separate windows.

 

Example layout

+------------------+------------------+
| System Metrics   |  Server Logs     |
| CPU: 28%         |  [INFO] Started  |
| Memory: 4.2GB    |  [INFO] Running  |
+------------------+------------------+
| Database Status                     |
| Connections: 14                     |
+------------------------------------+

   

Such layouts allow users to monitor multiple aspects of an application at the same time.

 

3. Mouse Support

Although terminal applications are often associated with keyboard-only interaction, modern terminals also support mouse input.

 

Jexer includes built-in mouse support, allowing users to interact with components using mouse clicks and movement.

 

Mouse support enables actions such as:

 

·      selecting menu items

·      clicking buttons

·      dragging windows

·      resizing panels

 

This feature makes terminal applications feel more intuitive and closer to graphical desktop applications.

 

Example

A user can click a button inside a dialog window to confirm an action instead of typing commands.

 

4. Keyboard Input Handling

Keyboard interaction remains a fundamental part of terminal applications, and Jexer provides robust support for handling keyboard input.

 

The library can detect various key events including:

 

·      character input

·      arrow keys

·      function keys

·      special keys such as Enter, Escape, and Tab

 

Developers can attach handlers to respond to these events and perform appropriate actions.

 

A list component may allow navigation using arrow keys:

> Server A
  Server B
  Server C

Pressing the down arrow moves the selection to the next item. This type of interaction makes navigation fast and efficient for users who prefer keyboard-driven workflows.

 

5. Layout System

Designing user interfaces requires organizing components in a structured layout. Jexer provides a layout system that helps developers arrange UI elements within windows.

 

Instead of manually calculating positions for each element, developers can rely on layout mechanisms to structure components logically.

 

This simplifies interface design and ensures that UI elements are aligned correctly.

 

For example, a window may contain:

 

·      labels describing input fields

·      text fields for user input

·      buttons for submitting forms

 

The layout system ensures that these components appear in the correct positions and maintain a consistent structure.

 

6. Dialogs and Widgets

Another important feature of Jexer is its collection of built-in widgets and dialog components. Widgets are reusable interface elements that allow developers to quickly build interactive applications.

 

Common widgets include:

·      buttons

·      text fields

·      labels

·      lists

·      checkboxes

·      menu bars

 

Dialogs are specialized windows used for user interaction such as confirmations or input prompts.

 

7. Terminal Compatibility

Terminals vary in how they support colors, cursor movement, and rendering capabilities. Handling these differences manually can be complicated.

 

Jexer abstracts many of these complexities by providing consistent behavior across different terminal environments.

 

The library manages:

·      screen refresh operations

·      cursor positioning

·      color handling

·      terminal resizing

 

This allows developers to focus on building their application rather than worrying about terminal-specific details.

  

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Design Philosophy of Jexer

  

Building applications for the terminal traditionally required developers to manage many low-level details such as cursor positioning, screen refresh logic, keyboard input handling, and manual drawing of text elements. This often made terminal application development complex and error-prone. Libraries like Jexer were created to simplify this process by providing a structured framework for building rich terminal applications.

 

The design philosophy of Jexer focuses on bringing modern application design principles to terminal environments. Instead of treating the terminal as a simple output stream, Jexer treats it as a full application environment capable of hosting windows, widgets, dialogs, and interactive components.

 

The core idea behind Jexer is to allow developers to build desktop-style applications that run inside a terminal while hiding the complexity of terminal rendering and input management.

 

1. Goals of Jexer

The primary goal of Jexer is to make it easier for Java developers to build powerful and structured terminal applications.

 

Some of the key goals include:

 

·      Simplifying terminal UI development

·      Providing reusable UI components

·      Supporting complex application layouts

·      Handling keyboard and mouse events automatically

 

Allowing developers to focus on application logic rather than terminal internals

 

Instead of manually writing ANSI escape sequences and managing terminal buffers, developers can use high-level components such as windows, menus, text fields, and dialogs.

 

This approach significantly reduces development complexity and improves maintainability.

 

2. Window-Based Terminal Applications

One of the most distinctive aspects of Jexer is its window-based interface model.

 

Traditional terminal applications usually display information in a single screen layout. In contrast, Jexer allows developers to create multiple windows that behave similarly to windows in a graphical desktop environment.

 

These windows can:

 

·      be opened and closed dynamically

·      contain different UI components

·      overlap with other windows

·      be moved or resized by the user

 

This design enables developers to build applications that feel very similar to desktop software, even though they run entirely inside a terminal.

 

For example, a Jexer application could include:

 

·      a dashboard window showing system metrics

·      a log viewer window displaying real-time logs

·      a configuration dialog for modifying settings

 

Each of these elements can operate independently within the terminal environment.

 

3. Event-Driven Architecture

Another important design principle used by Jexer is event-driven architecture.

 

Instead of continuously polling for input or manually handling keyboard events, Jexer processes user interactions through events.

 

Common events include:

 

·      key presses

·      mouse clicks

·      window focus changes

·      menu selections

·      dialog interactions

 

When an event occurs, Jexer automatically dispatches it to the appropriate component. Developers simply implement event handlers to respond to user actions.

 

This model is very similar to how graphical frameworks handle user interactions, making it easier for developers who are familiar with GUI development.

 

4. Separation of UI and Logic

A key principle in modern software design is the separation of user interface and application logic. Jexer encourages this approach by providing structured components that manage UI rendering and interaction.

 

With this design, developers can:

 

·      define UI components such as windows and dialogs

·      attach event handlers to respond to user actions

·      implement application logic separately from UI code

 

This separation improves code organization and makes applications easier to maintain and extend.

 

For example, a monitoring application might display system metrics in a window, while the logic responsible for retrieving those metrics runs independently in the background.

 

5. Terminal and Swing Support

An interesting feature of Jexer is its ability to run applications in both terminal environments and Java Swing windows.

 

This means the same application can operate in two different modes:

 

·      Inside a terminal window

·      Inside a graphical window using Swing

 

This dual capability allows developers to test and run their applications even in environments where a terminal interface may not be ideal.

 

It also demonstrates how Jexer bridges the gap between terminal based applications and graphical interfaces.

 

6. Bringing Desktop UI Concepts to the Terminal

Perhaps the most interesting aspect of Jexer’s design philosophy is its attempt to bring desktop style user interface concepts into the terminal.

 

Traditional terminal applications are often limited to simple menus or command-driven interfaces. Jexer expands this concept by introducing familiar UI patterns such as:

 

·      window managers

·      dialog boxes

·      menu bars

·      status bars

·      interactive widgets

 

These components allow developers to create terminal applications that behave very similarly to graphical desktop software.

 

The result is a powerful hybrid environment where applications retain the efficiency and portability of terminal programs while offering the usability and structure of graphical interfaces.

 

Find the below working Application.

 

JexerConceptDemo.java

package com.sample.app.chapter3;

import jexer.TAction;
import jexer.TApplication;
import jexer.TMessageBox;
import jexer.TStatusBar;
import jexer.TWindow;
import jexer.event.TMenuEvent;
import jexer.menu.TMenu;

public class JexerConceptDemo extends TApplication {

    private static final int MENU_EXIT = 100;
    private static final int MENU_ABOUT = 200;
    private static final int MENU_OPEN_LOG = 300;
    private static final int MENU_CLOSE_LOG = 400;

    // Keep reference to log window
    private TWindow logWindow = null;

    public JexerConceptDemo() throws Exception {

        super(TApplication.BackendType.SWING);

        createMenuBar();
        createDashboardWindow();
        createStatusBar();
    }

    private void createMenuBar() {

        TMenu fileMenu = addMenu("&File");
        fileMenu.addItem(MENU_OPEN_LOG, "&Open Log Viewer");
        fileMenu.addItem(MENU_CLOSE_LOG, "&Close Log Viewer");
        fileMenu.addItem(MENU_EXIT, "E&xit");

        addMenu("&Help")
            .addItem(MENU_ABOUT, "&About");
    }

    private void createDashboardWindow() {

        TWindow dashboard = addWindow("System Dashboard", 2, 2, 60, 15);

        dashboard.addLabel("CPU Usage: 32%", 2, 2);
        dashboard.addLabel("Memory: 4.1 GB / 16 GB", 2, 4);
        dashboard.addLabel("Active Connections: 12", 2, 6);

        dashboard.addLabel("Use File menu to open/close Log Viewer", 2, 9);
        dashboard.addLabel("Windows can overlap and move", 2, 10);
    }

    private void createStatusBar() {

        TWindow mainWindow = getActiveWindow();

        TStatusBar statusBar = mainWindow.newStatusBar(
            "Demo: Window UI | File → Open Log Viewer"
        );
    }

    private void openLogWindow() {

        // Prevent multiple log windows
        if (logWindow != null) {
            activateWindow(logWindow);
            return;
        }

        logWindow = addWindow("Application Logs", 10, 5, 50, 12);

        logWindow.addLabel("[INFO] Application started", 2, 2);
        logWindow.addLabel("[INFO] Connected to server", 2, 3);
        logWindow.addLabel("[WARN] CPU usage slightly high", 2, 4);
        logWindow.addLabel("[INFO] Monitoring active", 2, 5);

        // Close button
        logWindow.addButton("Close", 2, 8, new TAction() {
            public void DO() {
                closeLogWindow();
            }
        });
    }

    private void closeLogWindow() {

        if (logWindow != null) {
            closeWindow(logWindow);
            logWindow = null;
        }
    }

    @Override
    protected boolean onMenu(TMenuEvent event) {

        if (event.getId() == MENU_EXIT) {

            TMessageBox confirm = messageBox(
                "Exit",
                "Do you really want to exit?",
                TMessageBox.Type.YESNO
            );

            if (confirm.isYes()) {
                exit();
            }

            return true;
        }

        if (event.getId() == MENU_ABOUT) {

            messageBox(
                "About",
                "Jexer Demo Application\n" +
                "Shows window UI, menus and events\n" +
                "Running inside a terminal",
                TMessageBox.Type.OK
            );

            return true;
        }

        if (event.getId() == MENU_OPEN_LOG) {

            openLogWindow();
            return true;
        }

        if (event.getId() == MENU_CLOSE_LOG) {

            closeLogWindow();
            return true;
        }

        return super.onMenu(event);
    }

    public static void main(String[] args) throws Exception {

        JexerConceptDemo app = new JexerConceptDemo();
        app.run();
    }
}

Output

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Introducing Jexer

  

Modern software applications are often associated with graphical user interfaces (GUIs) that rely on windows, buttons, menus, and rich graphics. However, long before graphical interfaces became widespread, many powerful applications were built to run directly inside the terminal. These applications are known as Text User Interface (TUI) programs. Despite the dominance of GUIs and web applications today, TUIs continue to play an important role in development, system administration, and server environments.

 

In the Java ecosystem, one of the most powerful libraries for building terminal-based applications is Jexer. Jexer allows developers to create rich, interactive terminal applications that resemble desktop style programs. Instead of printing simple text output to the console, developers can build interfaces that contain multiple windows, menus, dialogs, input fields, and interactive components. This makes it possible to design complex applications that run entirely within a terminal.

 

At its core, Jexer provides a framework for building Text User Interfaces (TUIs) in Java. A TUI is an interface that uses characters, colors, and keyboard interactions to create structured screens inside a terminal. Unlike basic command-line programs that simply accept commands and print results, TUI applications provide an interactive environment where users can navigate menus, edit fields, open windows, and interact with the application in a more visual way.

 

Although modern development heavily focuses on web and graphical interfaces, TUIs still remain highly relevant. Many server environments do not have graphical desktops available, especially in cloud or containerized deployments. In such cases, terminal applications become the primary way to interact with systems. TUIs provide a balance between simple command-line tools and full graphical applications by offering structured and interactive interfaces while remaining lightweight and efficient.

 

Because of these advantages, TUIs are commonly used in a variety of real-world scenarios. For example, system dashboards built as terminal applications can display real-time metrics such as CPU usage, memory consumption, and network activity. Database management tools can allow users to browse tables, execute queries, and inspect results directly within a terminal window. Similarly, server monitoring applications often provide interactive dashboards that help administrators track system health without needing a graphical interface.

 

Many well-known tools in the software ecosystem are built using TUI concepts. These tools demonstrate how powerful terminal applications can be when designed with interactive components and structured layouts. Inspired by these ideas, libraries like Jexer make it possible for Java developers to build similar applications without having to manually manage terminal rendering or keyboard handling.

 

In this post, we will explore how Jexer enables developers to build modern terminal applications with features such as windows, dialogs, widgets, and event-driven input handling. By understanding the fundamentals of Jexer and Text User Interfaces, you will be able to create powerful console based applications that provide rich interaction while remaining lightweight and portable.

 

To give a quick idea of what a Jexer application looks like, imagine a terminal screen that contains multiple movable windows, menus at the top, status bars at the bottom, and interactive components inside each window. Even though the application runs inside a terminal, it behaves very similarly to a desktop application, providing a familiar and structured user experience.

 

1. What is Jexer?

Jexer is a Java library designed for building advanced terminal-based user interfaces. It provides a framework that allows developers to create structured and interactive applications inside a terminal window.

 

Unlike traditional console programs that simply print lines of text, Jexer introduces a window-based interface inside the terminal. Developers can create multiple windows, menus, dialog boxes, input fields, and widgets that users can interact with using the keyboard or mouse.

 

Some key capabilities of Jexer include:

 

·      Window-based UI inside a terminal

·      Event-driven keyboard and mouse input handling

·      Built-in UI components like buttons, menus, and dialogs

·      Support for terminal rendering and screen management

·      Ability to run both in terminal environments and Swing

 

Because of these features, applications built with Jexer can behave very similarly to desktop programs, even though they run entirely inside a terminal.

 

2. What is a TUI (Text User Interface)

A Text User Interface (TUI) is a type of user interface that displays structured screens using characters and text instead of graphical elements.

 

In a TUI application, the interface is created using:

 

·      characters

·      colors

·      keyboard input

·      cursor positioning

 

Rather than entering commands line-by-line like in a command-line interface (CLI), users interact with menus, forms, and windows displayed directly in the terminal.

 

For example, a typical TUI application might contain:

 

·      a menu bar at the top

·      multiple windows displaying different information

·      input fields for user data

·      navigation using arrow keys or keyboard shortcuts

 

TUIs were very common before graphical operating systems became widespread, but they continue to be widely used because of their efficiency and simplicity.

 

3. Why TUIs Still Matter

Even though graphical interfaces dominate modern applications, TUIs remain extremely valuable in many scenarios.

 

One of the main reasons is that many systems operate in environments where graphical interfaces are not available. Servers, containers, and remote systems are often accessed through terminal sessions where GUI applications cannot run.

 

TUIs offer several advantages in these environments.

 

·      Lightweight: TUI applications consume far fewer resources compared to graphical applications. They do not require graphical rendering engines or desktop environments.

 

·      Remote Friendly: Terminal-based applications work well over remote connections such as SSH. This makes them ideal for server management and cloud environments.

 

·      Faster Interaction: Many experienced users prefer keyboard-driven interfaces because they allow faster navigation and interaction compared to mouse-based systems.

 

·      Simplicity: TUI applications are easier to deploy and maintain because they have fewer dependencies compared to graphical applications.

 

Because of these benefits, TUIs remain widely used in system administration, DevOps tooling, and monitoring dashboards.

 

4. Typical Use Cases of TUI Applications

TUI applications are commonly used in environments where graphical interfaces are unnecessary or unavailable. Below are some typical scenarios where TUIs are particularly useful.

 

4.1 System Dashboards

Terminal dashboards can display real-time system information such as CPU usage, memory consumption, and network activity. These dashboards allow administrators to monitor system health without leaving the terminal.

 

For example, a TUI dashboard might show:

 

·      CPU utilization graphs

·      memory usage statistics

·      active processes

·      network traffic

 

With libraries like Jexer, developers can build similar dashboards for their own applications.

 

4.2 Database Tools

Database management often requires executing queries, browsing tables, and inspecting results. A TUI-based database tool allows developers or administrators to perform these tasks directly from the terminal.

 

Such tools may provide:

 

·      table navigation

·      query editors

·      result viewers

·      schema browsers

 

Because TUIs are lightweight, they are ideal for managing databases on remote servers.

 

4.3 Server Monitoring

Monitoring servers and services is another common use case for TUI applications. Administrators frequently need to monitor logs, track metrics, and inspect system behavior in real time.

 

A TUI monitoring application might display:

 

·      service status

·      log streams

·      resource usage

·      alerts and warnings

 

These applications are especially useful in production environments where remote access is common.

 

5. Example Applications Built with TUIs

Many well-known developer tools use TUI interfaces. These tools demonstrate how powerful terminal applications can be when designed with interactive components.

 

Examples include:

·      htop: an interactive process monitoring tool

·      Midnight Commander: a terminal-based file manager

·      nmtui: a network configuration interface

 

These applications provide rich user experiences even though they run entirely inside the terminal.

 

Libraries like Jexer allow Java developers to build similar applications without having to manually handle terminal rendering, keyboard events, or screen updates.

 

Find the below working Application.

 

DashboardApp.java

package com.sample.app.chapter3;

import static jexer.TCommand.cmHelp;
import static jexer.TCommand.cmMenu;
import static jexer.TCommand.cmQuit;
import static jexer.TKeypress.kbCtrlQ;
import static jexer.TKeypress.kbF1;
import static jexer.TKeypress.kbF10;

import jexer.TApplication;
import jexer.TMessageBox;
import jexer.TStatusBar;
import jexer.TWindow;
import jexer.event.TMenuEvent;

public class DashboardApp extends TApplication {

    private static final int MENU_EXIT = 2001;
    private static final int MENU_ABOUT = 2100;

    public DashboardApp() throws Exception {

        super(TApplication.BackendType.SWING);

        createMenuBar();
        createDashboardWindow();
    }

    private void createMenuBar() {

        addMenu("&File").addItem(MENU_EXIT, "E&xit");

        addMenu("&Edit");

        addMenu("&View");

        addMenu("&Help").addItem(MENU_ABOUT, "&About");
    }

    private void createDashboardWindow() {

        TWindow dashboard = addWindow("System Dashboard", 2, 2, 60, 16);

        dashboard.addLabel("CPU Usage: 32%", 2, 2);
        dashboard.addLabel("Memory: 4.1 GB / 16 GB", 2, 4);
        dashboard.addLabel("Active Connections: 12", 2, 6);
        dashboard.addLabel("Server Status: Running", 2, 8);

        dashboard.addLabel("Use menu or keyboard shortcuts to interact.", 2, 11);

        TStatusBar statusBar = dashboard.newStatusBar("Connected to server");

        statusBar.addShortcutKeypress(kbF1, cmHelp, "Help");
        statusBar.addShortcutKeypress(kbF10, cmMenu, "Menu");
        statusBar.addShortcutKeypress(kbCtrlQ, cmQuit, "Quit");
    }

    @Override
    protected boolean onMenu(TMenuEvent event) {

        if (event.getId() == MENU_EXIT) {

            TMessageBox confirm = messageBox("Exit Application", "Do you really want to exit?", TMessageBox.Type.YESNO);

            if (confirm.isYes()) {
                exit();
            }

            return true;
        }

        if (event.getId() == MENU_ABOUT) {

            messageBox("About", "System Dashboard\nBuilt using Jexer\nTerminal UI Demo", TMessageBox.Type.OK);

            return true;
        }

        return super.onMenu(event);
    }

    public static void main(String[] args) throws Exception {

        DashboardApp app = new DashboardApp();
        app.run();
    }
}

Output

  

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