Java

Catalog v8.

Installs a headless OpenJDK and the jdtls language server.

Select

[toolchains]
java = "21"

Choose the line in the [toolchains] table of limanix.toml and apply the change. Add Maven or Gradle in the same table to build projects.

Versions

Value	JDK	Notes
25	OpenJDK 25.x
21	OpenJDK 21.x	Recommended
17	OpenJDK 17.x

Lines come from the base Nixpkgs revision and receive its updates with each catalog release. The JDK is headless: it leaves out the graphical libraries, which a VM without a display does not use.

Use

Inside the VM, compile and run a class:

javac Main.java
java Main

Run jshell to try code interactively. JAVA_HOME points to the selected JDK in every session.

Other tools and JDKs

The selected JDK is also at /usr/lib/jvm/openjdk-<line>, where Gradle, IntelliJ IDEA and VS Code look for installed JDKs. When a project asks for another Java version, Gradle or the IDE downloads a generic Linux JDK, which runs with nix-ld, on in every LimaNix VM.

Editor support

The module installs jdtls for editors that support the Language Server Protocol; AstroNvim starts it for Java files. jdtls runs on its own JDK from Nixpkgs, independent of the selected line, and loads Lombok: the editor understands code that uses Lombok annotations.

Configuration and integration

Boundary	Contract
Public capability	lmx.capabilities.jdk.package, the newest selected JDK; lmx.capabilities.languageSupport.tools.jdtls; Java parser
Settings	JAVA_HOME; /usr/lib/jvm/openjdk-<line> for every selected line
Integration	Maven, Gradle and Quarkus run on the JDK of the capability
Services	No daemon

Corner cases

Case	Behavior or next step
A downloaded JDK does not start	Check that programs.nix-ld.enable is on, or select that Java line
A desktop Java program needs a display	The headless JDK cannot open windows; run the program on the Mac