Configuring Java LSP, and Debugger for Neovim with nvim-jdtls

Introduction

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Developing Java code in Neovim can be a seamless experience with the right Language Server Protocol (LSP) setup. In this blog post, we will explore how to enhance your Neovim environment for Java development by configuring nvim-jdtls. This plugin, available at nvim-jdtls, offers a comprehensive set of features tailored for Java, addressing challenges such as navigating to the definition of methods and classes outside your project.

Before we proceed, ensure you’ve checked out my Neovim configuration post, which complements this setup:

Prerequisites

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1. Neovim version >= 0.6.0

   Verify your Neovim version using:

   nvim --version
   

2. Java runtime environment 17 and above

   Install the desired Java version, ensuring it is 17 or above. For example, to install OpenJDK version 21:

   sudo apt install openjdk-21-jdk
   

   Set the JAVA_HOME environment variable to point to the JDK or JRE directory. Identify the correct path using:

   sudo update-alternatives --config java
   

   Set JAVA_HOME in your .bashrc or .zshrc:

   export JAVA_HOME=/path/to/openjdk-21
   

   For example:

   export JAVA_HOME=/usr/lib/jvm/java-21-openjdk-amd64
   

3. eclipse.jdt.ls

   Download and extract a snapshot build from http://download.eclipse.org/jdtls/snapshots/:

   wget https://download.eclipse.org/jdtls/snapshots/jdt-language-server-1.31.0-202312211634.tar.gz && sudo tar -C /usr/local -xzf jdt-language-server-1.31.0-202312211634.tar.gz
   

4. java-debug To debug java programs, load the java-debug extension. Install it on your neovim data folder ~/.local/share/nvim using the following commands

   git clone https://github.com/microsoft/java-debug.git ~/.local/share/nvim/java-debug
   cd ~/.local/share/nvim/java-debug
   ./mvnw clean install
   

Installing plugins

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1. nvim-jdtls

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Install the plugin using your preferred plugin manager. If using Lazy, add the following line to your init.lua file and install with :Lazy:

"mfussenegger/nvim-jdtls", -- java lsp

2. nvim-dap

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Install nvim-dap using your preferred plugin manager. Check out my nvim-dap configuration which provides a user-friendly UI as well as key mappings for debugging.

3. jdtls LSP

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Install jdtls lsp using Mason by initiating mason with :Mason and proceeding with the installation. Check out my Mason configuration if you haven’t setup Mason. Mason is just a plugin for managing LSPs, linters, formatters, and DAPs.

Configuration

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1. Avoid confict between nvim-lspconfig and nvim-jdtls

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Skip this step if you are not using nvim-lspconfig.

To avoid conficts, ensure you do not run nvim-lspconfig and nvim-jdtls simultaneously. Add the following setup_handler configuration to your nvim-lspconfig (in my case it’s ~/.config/nvim/lua/justice/plugins/lsp/lspconfig.lua):

-- empty function to ignore jdtls
local noop = function() end

require("mason-lspconfig").setup_handlers({
  function(server_name)
    lspconfig[server_name].setup({
      on_attach = on_attach,
      capabilities = capabilities,
    })
  end,
  ["jdtls"] = noop,
})

2. jdtls configuration

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Create a ~/.config/nvim/ftplugin/java.lua file with the following code for jdtls configuration:

local jdtls_bin = vim.fn.stdpath("data") .. "/mason/bin/jdtls"

local keymap = vim.keymap

local opts = { noremap = true, silent = true }

local lsp_attach = function(client, bufnr)
  require("jdtls.dap").setup_dap_main_class_configs() -- Discover main classes for debugging

  opts.buffer = bufnr

  -- set keybinds. Copied my lspconfig keybinds here
end

local config = {
  cmd = { jdtls_bin },
  root_dir = vim.fs.dirname(vim.fs.find({ "gradlew", ".git", "mvnw" }, { upward = true })[1]),
  on_attach = lsp_attach,
  init_options = {
    bundles = {
      vim.fn.glob(vim.fn.stdpath("data") .. "/java-debug/com.microsoft.java.debug.plugin/target/com.microsoft.java.debug.plugin-*.jar", 1),
    },
  },
}
require("jdtls").start_or_attach(config)

3. nvim-dap configuration

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Given that you have already installed nvim-dap, nvim-jdtls provides integration with nvim-dap, so you don’t need to configure Java debug adapters; nvim-jdtls adds that for you automatically. The only thing you’ll need to do is add a java configuration for debugging. Check out their wiki for more details. Add the following configuration to your nvim-dap plugin configuration file

require("dap").configurations = {
  java = {
    {
      type = "java",
      name = "Debug",
      request = "launch",
      program = "${file}",
    },
  },

  -- configurations for other languages
}

My configuration files

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Explore my configuration files by visiting lspconfig.lua, java.lua and dap.lua.

Conclusion

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Kudos on completing the setup! Your Neovim environment is now finely tuned for Java development with the configured Java LSP. Wishing you smooth coding sessions ahead - Happy coding!