kantanj

kantanj is a small, single-file C utility that helps you create, build, run and manage minimal Java (Maven) projects from the command line. It was designed as a pragmatic, portable replacement for a shell helper script: it detects Java via which java, corrects JAVA_HOME when necessary, creates a basic Maven pom.xml and a starter App.java, and wraps mvn for building and running.

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Installation

curl -fsSL https://raw.githubusercontent.com/nthnn/kantanj/refs/heads/main/install.sh | bash

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Features

• Create a minimal Maven project (pom + src/main/java/.../App.java) from a package name.
• Build the project with Maven (executes mvn -DskipTests package).
• Run the project's JAR (builds automatically if needed).
• Clean the project's target directory.
• Best-effort install helper to install JDK 21 and Maven via apt (Debian/Ubuntu).
• Detects Java via which java and computes the correct JAVA_HOME (fixes cases when JAVA_HOME was incorrectly set to the java binary).
• Small, portable C code (single translation unit).

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Requirements

• Linux (tested on Debian/Ubuntu-like systems). Many utilities rely on standard Unix tools.
• gcc (to build kantanj.c) or any compatible C compiler.
• mvn (Apache Maven) — kantanj can attempt to install Maven via apt when using install command.
• java — a JDK (OpenJDK/Temurin) is required to build and run projects. kantanj attempts to detect and fix JAVA_HOME where possible.

Note: The built-in install command attempts apt installs and Adoptium repo steps; it is not guaranteed to work for all distros. If your distro is not Debian/Ubuntu-based, install Java and Maven using your platform package manager.

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Quick start

1. Build the program:

gcc -O2 -std=c11 -Wall -Wextra -o kantanj kantanj.c

2. (Optional) Install to /usr/local/bin:

sudo install -m 0755 kantanj /usr/local/bin/kantanj

3. Create a project:

kantanj create helloworld com.example.hello

4. Build:

kantanj build helloworld

5. Run:

kantanj run helloworld arg1 arg2

6. Clean:

kantanj clean helloworld

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Commands & examples

Usage: kantanj <command> [args]
Commands:
  install                    Install JDK 21 and Maven (attempt via apt)
  create <name> <package>    Create a basic maven project (e.g. com.example)
  build <name>               Build project using mvn (uses ~/.m2/settings.xml)
  run <name> [args...]       Run project's jar (builds if needed)
  clean <name>               Remove project's target directory

Examples

Create a project helloworld with package com.example.hello:

kantanj create helloworld com.example.hello

This creates:

helloworld/
  pom.xml
  src/main/java/com/example/hello/App.java

The pom.xml will use groupId = com.example.hello and artifactId = helloworld. The main class will be com.example.hello.App.

Build:

kantanj build helloworld

Run (passes args to Java program):

kantanj run helloworld foo bar

Clean:

kantanj clean helloworld

Install prerequisites (try to install JDK 21 + Maven via apt; may prompt for sudo):

sudo kantanj install

or, from non-root:

kantanj install

kantanj will try to use sudo when needed.

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How JAVA_HOME is handled

Many Java tools (including Maven) expect JAVA_HOME to refer to the JDK home directory (for example /usr/lib/jvm/temurin-21-jdk-amd64), not to the java binary itself.

kantanj:

1. Detects Java using which java (so it follows the user's PATH).
2. Resolves symlinks with realpath.
3. Converts the path of the java binary to a reasonable JAVA_HOME (if .../bin/java is detected, it uses the parent directory as JAVA_HOME).
4. Sets JAVA_HOME for the process that runs Maven (so mvn sees a valid JAVA_HOME even if the environment was set wrongly).

This approach fixes the common situation where JAVA_HOME is accidentally set to /usr/lib/jvm/temurin-21-jdk-amd64/bin/java (binary) instead of /usr/lib/jvm/temurin-21-jdk-amd64 (home).

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Development / Build

Build locally:

gcc -O2 -std=c11 -Wall -Wextra -o kantanj kantanj.c

Turn on more warnings (optional):

gcc -O2 -std=c11 -Wall -Wextra -Wpedantic -o kantanj kantanj.c

Run the program locally without installing:

./kantanj create myproject com.example.myproj
./kantanj build myproject
././kantanj run myproject

If changes are made and you want to install the binary:

sudo install -m 0755 kantanj /usr/local/bin/kantanj

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Design & implementation notes

• kantanj.c is a single C file intentionally kept self-contained for simplicity.
• The program uses system() for a few operations (e.g. calling mvn, apt-get, or rm -rf). This keeps the code straightforward, but be mindful of shell injection if you integrate the tool into other automated flows — do not pass untrusted data into kantanj commands that would be composed into shell commands.
• File writing and directory creation are implemented in C (no shell required).
• create writes a minimal pom.xml with maven-shade-plugin configured so package produces an executable fat JAR.
• install attempts apt installs and a best-effort attempt to add the Adoptium apt repo. It does not implement tarball extraction and full update-alternatives registration. If install fails, install JDK/Maven manually for your platform.

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Troubleshooting

The JAVA_HOME environment variable is not defined correctly (Maven error)

• This means JAVA_HOME points to a path Maven does not accept (commonly the java binary). kantanj attempts to detect and correct JAVA_HOME automatically. To verify:

  which java
  realpath $(which java)
  echo $JAVA_HOME

• If echo $JAVA_HOME prints something ending with /bin/java, correct it:

  export JAVA_HOME=/usr/lib/jvm/temurin-21-jdk-amd64

  Then re-run kantanj build ....

Maven download failures (network / 502s)

• kantanj writes a minimal ~/.m2/settings.xml that mirrors central to repo1.maven.org. If your environment uses a corporate proxy or internal mirror, adjust ~/.m2/settings.xml accordingly.

apt install fails on non-Debian systems

• The install command targets Debian/Ubuntu. For other distros, use the distro's package manager (dnf, yum, pacman, zypper) or install a JDK manually.

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License

Copyright 2025 - Nathanne Isip

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the “Software”), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

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Changelog

• v0.1 — initial single-file C implementation:

  • create, build, run, clean commands.
  • install helper (apt-focused).
  • JAVA_HOME auto-correction (computed from which java).