java: add module

modules/programs/java.nix

@@ -0,0 +1,46 @@
+# This module provides JAVA_HOME, with a different way to install java locally.
+# This module is modified from the NixOS module `programs.java`
+
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let
+
+  cfg = config.programs.java;
+
+in {
+  meta.maintainers = with maintainers; [ ShamrockLee ];
+
+  options = {
+    programs.java = {
+      enable = mkEnableOption "" // {
+        description = ''
+          Install the Java development kit and set the <envar>JAVA_HOME</envar>
+          variable.
+        '';
+      };
+
+      package = mkOption {
+        type = types.package;
+        default = pkgs.jdk;
+        defaultText = "pkgs.jdk";
+        description = ''
+          Java package to install. Typical values are
+          <literal>pkgs.jdk</literal> or <literal>pkgs.jre</literal>.
+        '';
+      };
+    };
+  };
+
+  config = mkIf cfg.enable {
+    home.packages = [ cfg.package ];
+
+    home.sessionVariables = {
+      JAVA_HOME = fileContents (pkgs.runCommandLocal "java-home" { } ''
+        source "${cfg.package}/nix-support/setup-hook"
+        echo "$JAVA_HOME" > $out
+      '');
+    };
+  };
+}