Java

The Java module adds a JDK to your shell, with optional Maven, Gradle, and the Eclipse JDT Language Server. devenv sets JAVA_HOME to the JDK you select.

Language Server

The language server can run on a different JDK from your project. There are two ways to tell it which project JDK to use:

• java.home sets one default project JDK in Neovim. VS Code deprecates this setting.
• java.configuration.runtimes maps Java versions, such as JavaSE-17, to installed JDKs. Use this for multiple JDKs or explicit version mappings.

Maven and Gradle projects still set their Java language version in pom.xml or build.gradle.

Gradle projects

The Eclipse JDT Language Server, which powers Java support in VS Code, Neovim, and most other editors, imports a Gradle project by running Gradle. Without a project JDK configured, it may run Gradle on the server’s JDK.

Set java.import.gradle.java.home to the project JDK to run the import on the same JDK as your shell.

VS Code

The Java extension bundles its own language server. It normally detects project JDKs from JAVA_HOME and the build configuration. Set languages.java.lsp.enable = false if you only use this extension.

Generate the workspace settings from devenv.nix, so the JDK path stays in sync with your project:

{ config, lib, ... }:
let
  jdk = config.languages.java.jdk.package;
  major = lib.versions.major jdk.version;
in
{
  files.".vscode/settings.json".json = {
    "java.configuration.runtimes" = [
      {
        name = "JavaSE-${major}";
        path = jdk.home;
        default = true;
      }
    ];
    "java.import.gradle.java.home" = jdk.home;
  };
}

The extension’s bundled runtime starts the server; the runtime mapping registers the project JDK. See Microsoft’s Configure Runtime for Projects.

Neovim (LazyVim)

Save this as .lazy.lua in your project root. LazyVim loads it as a project-local configuration.

local profile = vim.env.DEVENV_PROFILE
if not profile then
  return {}
end

local java = {
  cmd = { profile .. "/bin/jdtls" },
  settings = {
    java = {
      home = vim.env.JAVA_HOME,
      import = { gradle = { java = { home = vim.env.JAVA_HOME } } },
    },
  },
}

return {
  {
    "neovim/nvim-lspconfig",
    opts = {
      servers = {
        jdtls = vim.tbl_extend("force", java, { mason = false }),
      },
    },
  },
  {
    "mfussenegger/nvim-jdtls",
    optional = true,
    opts = java,
  },
}

Options

languages.java.enable

Whether to enable tools for Java development.

Type: boolean

Default:

false

Example:

true

Declared by:

• https://github.com/cachix/devenv/blob/main/src/modules/languages/java.nix

languages.java.gradle.enable

Whether to enable gradle.

Type: boolean

Default:

false

Example:

true

Declared by:

• https://github.com/cachix/devenv/blob/main/src/modules/languages/java.nix

languages.java.gradle.package

The Gradle package to use. The Gradle package by default inherits the JDK from languages.java.jdk.package.

Type: package

Default:

pkgs.gradle.override { java = cfg.jdk.package; }

Declared by:

• https://github.com/cachix/devenv/blob/main/src/modules/languages/java.nix

languages.java.jdk.package

The JDK package to use. This will also become available as JAVA_HOME.

Type: package

Default:

pkgs.jdk

Example:

pkgs.jdk8

Declared by:

• https://github.com/cachix/devenv/blob/main/src/modules/languages/java.nix

languages.java.lsp.enable

Whether to enable Java Language Server.

Type: boolean

Default:

true

Example:

true

Declared by:

• https://github.com/cachix/devenv/blob/main/src/modules/languages/java.nix

languages.java.lsp.package

The Java language server package to use. The language server runs on the JDK packaged with it, not on languages.java.jdk.package. Configure the project JDK in your editor; see the Java guide.

Type: package

Default:

pkgs.jdt-language-server

Declared by:

• https://github.com/cachix/devenv/blob/main/src/modules/languages/java.nix

languages.java.maven.enable

Whether to enable maven.

Type: boolean

Default:

false

Example:

true

Declared by:

• https://github.com/cachix/devenv/blob/main/src/modules/languages/java.nix

languages.java.maven.package

The Maven package to use. The Maven package by default inherits the JDK from languages.java.jdk.package.

Type: package

Default:

pkgs.maven.override { jdk_headless = cfg.jdk.package; }

Declared by:

• https://github.com/cachix/devenv/blob/main/src/modules/languages/java.nix