feat: add Java support with jdtls, DAP, neotest and google-java-format

- Add nvim-jdtls for Java LSP with Maven/Gradle project detection
- Create ftplugin/java.lua for automatic jdtls startup and keymaps
- Enable nvim-dap with java-debug-adapter for breakpoint debugging
- Add neotest with neotest-java adapter for JUnit 5 test runner
- Add NeotestJavaDownload command for JUnit jar setup on Neovim < 0.12
- Configure google-java-format via conform.nvim
- Add java treesitter parser and <leader>j which-key group
- Mason auto-installs jdtls, java-debug-adapter, java-test, google-java-format

ftplugin/java.lua

@@ -0,0 +1,121 @@
+-- ftplugin/java.lua
+-- This file is automatically loaded when a Java file is opened.
+-- It configures jdtls (Eclipse JDT Language Server) for Java development.
+
+local jdtls = require 'jdtls'
+
+-- Mason install paths
+local mason_path = vim.fn.stdpath 'data' .. '/mason/packages'
+local jdtls_path = mason_path .. '/jdtls'
+local java_debug_path = mason_path .. '/java-debug-adapter'
+local java_test_path = mason_path .. '/java-test'
+
+-- Detect the OS for the jdtls config directory
+local os_config = 'config_linux'
+if vim.fn.has 'mac' == 1 then
+  os_config = 'config_mac'
+elseif vim.fn.has 'win32' == 1 then
+  os_config = 'config_win'
+end
+
+-- Find the launcher jar
+local launcher_jar = vim.fn.glob(jdtls_path .. '/plugins/org.eclipse.equinox.launcher_*.jar')
+
+-- Determine the project name for workspace isolation
+local project_name = vim.fn.fnamemodify(vim.fn.getcwd(), ':p:h:t')
+local workspace_dir = vim.fn.stdpath 'data' .. '/jdtls-workspace/' .. project_name
+
+-- Find the root directory of the project
+local root_dir = require('jdtls.setup').find_root { 'pom.xml', 'build.gradle', 'gradlew', '.git', 'mvnw' }
+
+-- Collect debug and test bundles
+local bundles = {}
+
+-- java-debug-adapter
+local debug_jar = vim.fn.glob(java_debug_path .. '/extension/server/com.microsoft.java.debug.plugin-*.jar', true)
+if debug_jar ~= '' then
+  table.insert(bundles, debug_jar)
+end
+
+-- java-test
+local test_jars = vim.split(vim.fn.glob(java_test_path .. '/extension/server/*.jar', true), '\n')
+for _, jar in ipairs(test_jars) do
+  if jar ~= '' then
+    table.insert(bundles, jar)
+  end
+end
+
+-- jdtls configuration
+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',
+    '-Xmx1g',
+    '--add-modules=ALL-SYSTEM',
+    '--add-opens', 'java.base/java.util=ALL-UNNAMED',
+    '--add-opens', 'java.base/java.lang=ALL-UNNAMED',
+    '-jar', launcher_jar,
+    '-configuration', jdtls_path .. '/' .. os_config,
+    '-data', workspace_dir,
+  },
+
+  root_dir = root_dir,
+
+  settings = {
+    java = {
+      signatureHelp = { enabled = true },
+      contentProvider = { preferred = 'fernflower' },
+      completion = {
+        favoriteStaticMembers = {
+          'org.junit.jupiter.api.Assertions.*',
+          'org.mockito.Mockito.*',
+          'org.mockito.ArgumentMatchers.*',
+          'java.util.Objects.requireNonNull',
+          'java.util.Objects.requireNonNullElse',
+        },
+      },
+      sources = {
+        organizeImports = {
+          starThreshold = 9999,
+          staticStarThreshold = 9999,
+        },
+      },
+    },
+  },
+
+  init_options = {
+    bundles = bundles,
+  },
+
+  -- Called when jdtls attaches to a buffer
+  on_attach = function(_, bufnr)
+    -- Enable debug and test support after LSP is ready
+    jdtls.setup_dap { hotcodereplace = 'auto' }
+    require('jdtls.dap').setup_dap_main_class_configs()
+
+    local opts = { buffer = bufnr }
+
+    -- Java-specific keymaps under <leader>j
+    vim.keymap.set('n', '<leader>ji', jdtls.organize_imports, vim.tbl_extend('force', opts, { desc = '[J]ava Organize [I]mports' }))
+    vim.keymap.set('n', '<leader>jc', jdtls.extract_constant, vim.tbl_extend('force', opts, { desc = '[J]ava Extract [C]onstant' }))
+    vim.keymap.set('v', '<leader>jm', function() jdtls.extract_method(true) end, vim.tbl_extend('force', opts, { desc = '[J]ava Extract [M]ethod' }))
+    vim.keymap.set('v', '<leader>jv', jdtls.extract_variable, vim.tbl_extend('force', opts, { desc = '[J]ava Extract [V]ariable' }))
+
+    -- Test keymaps using neotest
+    local neotest = require 'neotest'
+    vim.keymap.set('n', '<leader>jt', function() neotest.run.run() end, vim.tbl_extend('force', opts, { desc = '[J]ava Run [T]est (cursor)' }))
+    vim.keymap.set('n', '<leader>jf', function() neotest.run.run(vim.fn.expand '%') end, vim.tbl_extend('force', opts, { desc = '[J]ava Run Tests [F]ile' }))
+    vim.keymap.set('n', '<leader>js', function() neotest.summary.toggle() end, vim.tbl_extend('force', opts, { desc = '[J]ava Test [S]ummary' }))
+    vim.keymap.set('n', '<leader>jo', function() neotest.output.open { enter = true } end, vim.tbl_extend('force', opts, { desc = '[J]ava Test [O]utput' }))
+
+    -- Debug test under cursor
+    vim.keymap.set('n', '<leader>jd', function() neotest.run.run { strategy = 'dap' } end, vim.tbl_extend('force', opts, { desc = '[J]ava [D]ebug Test' }))
+  end,
+}
+
+-- Start or attach jdtls
+jdtls.start_or_attach(config)

init.lua

@@ -334,6 +334,7 @@ require('lazy').setup({
         { '<leader>h', group = 'Git [H]unk', mode = { 'n', 'v' } },
         { '<leader>g', group = '[G]it' },
         { '<leader>gf', group = '[F]ind' },
+        { '<leader>j', group = '[J]ava' },
       },
     },
   },
@@ -672,6 +673,10 @@ require('lazy').setup({
         'vue-language-server', -- Vue.js LSP (Volar)
         'eslint-lsp', -- ESLint LSP
         'prettierd', -- Prettier daemon (formatter)
+        'jdtls', -- Java LSP (Eclipse JDT)
+        'java-debug-adapter', -- Java debug adapter
+        'java-test', -- Java test runner
+        'google-java-format', -- Java formatter
       }
 
       require('mason-tool-installer').setup { ensure_installed = ensure_installed }
@@ -749,6 +754,7 @@ require('lazy').setup({
         css = { 'prettierd', 'prettier', stop_after_first = true },
         html = { 'prettierd', 'prettier', stop_after_first = true },
         json = { 'prettierd', 'prettier', stop_after_first = true },
+        java = { 'google-java-format' },
       },
     },
   },
@@ -913,13 +919,59 @@ require('lazy').setup({
     opts = {},
   },
 
+  { -- Java LSP support via jdtls
+    'mfussenegger/nvim-jdtls',
+    ft = 'java',
+  },
+
+  { -- Test runner framework
+    'nvim-neotest/neotest',
+    dependencies = {
+      'nvim-neotest/nvim-nio',
+      'nvim-lua/plenary.nvim',
+      'nvim-treesitter/nvim-treesitter',
+      'rcasia/neotest-java', -- JUnit 5 adapter
+    },
+    config = function()
+      require('neotest').setup {
+        adapters = {
+          require 'neotest-java',
+        },
+      }
+
+      -- Command to download JUnit jar on machines without Neovim 0.12+
+      vim.api.nvim_create_user_command('NeotestJavaDownload', function()
+        local version = '1.10.1'
+        local dir = vim.fn.stdpath 'data' .. '/neotest-java'
+        local jar = dir .. '/junit-platform-console-standalone-' .. version .. '.jar'
+        if vim.fn.filereadable(jar) == 1 then
+          vim.notify('JUnit jar already exists at ' .. jar, vim.log.levels.INFO)
+          return
+        end
+        vim.fn.mkdir(dir, 'p')
+        local url = 'https://repo1.maven.org/maven2/org/junit/platform/junit-platform-console-standalone/'
+          .. version
+          .. '/junit-platform-console-standalone-'
+          .. version
+          .. '.jar'
+        vim.notify('Downloading JUnit Platform Console Standalone ' .. version .. '...', vim.log.levels.INFO)
+        vim.fn.system { 'curl', '-L', '-o', jar, url }
+        if vim.v.shell_error == 0 then
+          vim.notify('JUnit jar downloaded successfully!', vim.log.levels.INFO)
+        else
+          vim.notify('Failed to download JUnit jar', vim.log.levels.ERROR)
+        end
+      end, { desc = 'Download JUnit Platform Console Standalone jar for neotest-java' })
+    end,
+  },
+
   { -- Highlight, edit, and navigate code
     'nvim-treesitter/nvim-treesitter',
     build = ':TSUpdate',
     config = function()
       ---@diagnostic disable-next-line: missing-fields
       require('nvim-treesitter.configs').setup {
-        ensure_installed = { 'bash', 'c', 'css', 'diff', 'html', 'javascript', 'json', 'lua', 'luadoc', 'markdown', 'markdown_inline', 'query', 'tsx', 'typescript', 'vim', 'vimdoc', 'vue' },
+        ensure_installed = { 'bash', 'c', 'css', 'diff', 'html', 'java', 'javascript', 'json', 'lua', 'luadoc', 'markdown', 'markdown_inline', 'query', 'tsx', 'typescript', 'vim', 'vimdoc', 'vue' },
         auto_install = true,
         highlight = { enable = true },
         indent = { enable = true },
@@ -936,7 +988,7 @@ require('lazy').setup({
   --  Here are some example plugins that I've included in the Kickstart repository.
   --  Uncomment any of the lines below to enable them (you will need to restart nvim).
   --
-  -- require 'kickstart.plugins.debug',
+  require 'kickstart.plugins.debug',
   -- require 'kickstart.plugins.indent_line',
   -- require 'kickstart.plugins.lint',
   -- require 'kickstart.plugins.autopairs',

lua/kickstart/plugins/debug.lua

@@ -81,6 +81,7 @@ return {
       ensure_installed = {
         -- Update this to ensure that you have the debuggers for the langs you want
         'delve',
+        'java-debug-adapter',
       },
     }