add jdtls maybe

config/programs/vim/default.nix

@@ -1,5 +1,20 @@
 {pkgs, ...}: let
   dsquotes = "''";
+  nvim-jdtls = pkgs.stdenvNoCC.mkDerivation rec {
+    name = "nvim-jdtls.lua";
+    src = ./nvim-jdtls.lua;
+    dontUnpack = true;
+    java = pkgs.openjdk;
+    jdtLanguageServer = pkgs.jdt-language-server;
+    buildInputs = [java jdtLanguageServer];
+    buildPhase = ''
+      export launcher="$(ls $jdtLanguageServer/share/java/plugins/org.eclipse.equinox.launcher_* | sort -V | tail -n1)"
+      substituteAll $src nvim-jdtls.lua
+    '';
+    installPhase = ''
+      cp nvim-jdtls.lua $out
+    '';
+  };
 in {
   programs.neovim = {
     enable = true;
@@ -65,6 +80,10 @@ in {
         plugin = rust-tools-nvim;
         config = "lua dofile(\"${./rust-tools.lua}\")";
       }
+      {
+        plugin = nvim-jdtls;
+        config = "lua dofile(\"${nvim-jdtls}\")";
+      }
       nvim-dap
     ];
   };

config/programs/vim/nvim-jdtls.lua

@@ -0,0 +1,36 @@
+vim.api.nvim_create_autocmd({"FileType"}, {
+    pattern = {"java"},
+    callback = function()
+        local project_name = vim.fn.fnamemodify(vim.fn.getcwd(), ':p:h:t')
+        local workspace_dir = '@userhome@/.cache/jdtls/' .. project_name
+
+        local config = {
+            cmd = {
+                '@java@',
+                '-Declipse.application=org.eclipse.jdt.ls.core.id1',
+                '-Dosgi.bundles.defaultStartLevel=4',
+                '-Declipse.product=org.eclipse.jdt.ls.core.product',
+                '-Dlog.protocol=true',
+                '-Dlog.level=ALL',
+                '-Xms1g',
+                '--add-modules=ALL-SYSTEM',
+                '--add-opens', 'java.base/java.util=ALL-UNNAMED',
+                '--add-opens', 'java.base/java.lang=ALL-UNNAMED',
+                '-jar', '@launcher@',
+                '-configuration', '@jdtLanguageServer@/share/config',
+                '-data', workspace_dir,
+            }
+
+            root_dir = require('jdtls.setup').find_root({'.git', 'mvnw', 'gradlew'}),
+            settings = {
+                java = {
+                }
+            },
+            init_options = {
+                bundles = {}
+            },
+        };
+
+        require('jdtls').start_or_attach(config)
+    end
+})