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nvim-jdtls

Extensions for the built-in Language Server Protocol support in Neovim (>= 0.6.0) for eclipse.jdt.ls.

Audience

This project follows the KISS principle and targets users with some experience with Neovim, Java and its build tools Maven or Gradle who prefer configuration as code over GUI configuration. Ease of use is not the main priority.

If you prioritize ease of use over simplicity, you may want to use an alternative:

Extensions

  • organize_imports function to organize imports
  • extract_variable function to introduce a local variable
  • extract_variable_all function to introduce a local variable and replace all occurrences.
  • extract_constant function to extract a constant
  • extract_method function to extract a block of code into a method
  • Open class file contents
  • Code action extensions
    • Generate constructors
    • Generate toString function
    • hashCode and equals generation.
    • Extract variables or methods
    • Generate delegate methods
    • Move package, instance method, static method or type
    • Signature refactoring
  • javap command to show bytecode of current file
  • jol command to show memory usage of current file (jol_path must be set)
  • jshell command to open up jshell with classpath from project set
  • Debugger support via nvim-dap
  • Optional vscode-java-test extensions
    • Generate tests via require("jdtls.tests").generate()
    • Jump to tests or subjects via require("jdtls.tests").goto_subjects()

Take a look at a demo to see some of the functionality in action.

Plugin Installation

  • Requires Neovim (Latest stable (recommended) or nightly)
  • nvim-jdtls is a plugin. Install it like any other Vim plugin:
    • git clone https://github.com/mfussenegger/nvim-jdtls.git ~/.config/nvim/pack/plugins/start/nvim-jdtls
    • Or with vim-plug: Plug 'mfussenegger/nvim-jdtls'
    • Or with packer.nvim: use 'mfussenegger/nvim-jdtls'
    • Or any other plugin manager

Language Server Installation

Install eclipse.jdt.ls by following their Installation instructions.

Configuration (quickstart)

Add the following to ~/.config/nvim/ftplugin/java.lua (See :help base-directory):

local config = {
    cmd = {'/path/to/jdt-language-server/bin/jdtls'},
    root_dir = vim.fs.dirname(vim.fs.find({'gradlew', '.git', 'mvnw'}, { upward = true })[1]),
}
require('jdtls').start_or_attach(config)

Important:

  • eclipse.jdt.ls requires Java 17
  • The jdtls script requires Python 3.9
  • You'll have to teach eclipse.jdt.ls about your JDK installations by setting up runtimes if your projects use a different Java version than the one you're using for eclipse.jdt.ls itself. See Java XY language features are not available in the troubleshooting section further below to learn how to do that.

This should get you started, but will create temporary eclipse data folders when you open a project. Please read the Configuration (verbose) section if you want more control over the configuration or want to understand how things work.

Configuration (verbose)

To configure nvim-jdtls, add the following in ftplugin/java.lua within the Neovim configuration base directory (e.g. ~/.config/nvim/ftplugin/java.lua, see :help base-directory).

Watch out for the 💀, it indicates that you must adjust something.

-- See `:help vim.lsp.start_client` for an overview of the supported `config` options.
local config = {
  -- The command that starts the language server
  -- See: https://github.com/eclipse/eclipse.jdt.ls#running-from-the-command-line
  cmd = {

    -- 💀
    'java', -- or '/path/to/java17_or_newer/bin/java'
            -- depends on if `java` is in your $PATH env variable and if it points to the right version.

    '-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', '/path/to/jdtls_install_location/plugins/org.eclipse.equinox.launcher_VERSION_NUMBER.jar',
         -- ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^                                       ^^^^^^^^^^^^^^
         -- Must point to the                                                     Change this to
         -- eclipse.jdt.ls installation                                           the actual version


    -- 💀
    '-configuration', '/path/to/jdtls_install_location/config_SYSTEM',
                    -- ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^        ^^^^^^
                    -- Must point to the                      Change to one of `linux`, `win` or `mac`
                    -- eclipse.jdt.ls installation            Depending on your system.


    -- 💀
    -- See `data directory configuration` section in the README
    '-data', '/path/to/unique/per/project/workspace/folder'
  },

  -- 💀
  -- This is the default if not provided, you can remove it. Or adjust as needed.
  -- One dedicated LSP server & client will be started per unique root_dir
  --
  -- vim.fs.root requires Neovim 0.10.
  -- If you're using an earlier version, use: require('jdtls.setup').find_root({'.git', 'mvnw', 'gradlew'}),
  root_dir = vim.fs.root(0, {".git", "mvnw", "gradlew"})

  -- Here you can configure eclipse.jdt.ls specific settings
  -- See https://github.com/eclipse/eclipse.jdt.ls/wiki/Running-the-JAVA-LS-server-from-the-command-line#initialize-request
  -- for a list of options
  settings = {
    java = {
    }
  },

  -- Language server `initializationOptions`
  -- You need to extend the `bundles` with paths to jar files
  -- if you want to use additional eclipse.jdt.ls plugins.
  --
  -- See https://github.com/mfussenegger/nvim-jdtls#java-debug-installation
  --
  -- If you don't plan on using the debugger or other eclipse.jdt.ls plugins you can remove this
  init_options = {
    bundles = {}
  },
}
-- This starts a new client & server,
-- or attaches to an existing client & server depending on the `root_dir`.
require('jdtls').start_or_attach(config)

The ftplugin/java.lua logic is executed each time a FileType event triggers. This happens every time you open a .java file or when you invoke :set ft=java:

You can also find more complete configuration examples in the Wiki.

If you have trouble getting jdtls to work, please read the Troubleshooting section.

data directory configuration

eclipse.jdt.ls stores project specific data within the folder set via the -data flag. If you're using eclipse.jdt.ls with multiple different projects you must use a dedicated data directory per project.

An example how you could accomplish that is to infer the workspace directory name from the current working directory:

-- If you started neovim within `~/dev/xy/project-1` this would resolve to `project-1`
local project_name = vim.fn.fnamemodify(vim.fn.getcwd(), ':p:h:t')

local workspace_dir = '/path/to/workspace-root/' .. project_name
--                                               ^^
--                                               string concattenation in Lua

local config = {
  cmd = {
    ...,

    '-data', workspace_dir,

    ...,
  }
}

... is not valid Lua in this context. It is meant as placeholder for the other options from the Configuration section above.)

nvim-lspconfig and nvim-jdtls differences

Both nvim-lspconfig and nvim-jdtls use the client built into neovim:

  ┌────────────┐           ┌────────────────┐
  │ nvim-jdtls │           │ nvim-lspconfig │
  └────────────┘           └────────────────┘
       |                         |
      start_or_attach           nvim_lsp.jdtls.setup
       │                              |
       │                             setup java filetype hook
       │    ┌─────────┐                  │
       └───►│ vim.lsp │◄─────────────────┘
            └─────────┘
                .start_client
                .buf_attach_client

Some differences between the two:

  • The setup of lspconfig creates a java filetype hook itself and provides some defaults for the cmd of the config.
  • nvim-jdtls delegates the choice when to call start_or_attach to the user.
  • nvim-jdtls adds some logic to handle jdt:// URIs. These are necessary to load source code from third party libraries or the JDK.
  • nvim-jdtls adds some additional handlers and sets same extra capabilities to enable all the extensions.

You could use either to start the eclipse.jdt.ls client, but it is recommended to use the start_or_attach method from nvim-jdtls because of the additional capabilities it configures and because of the jdt:// URI handling.

You must not use both at the same time for java. You'd end up with two clients and two language server instances.

UI picker customization

Tip: You can get a better UI for code-actions and other functions by overriding the jdtls.ui picker. See UI Extensions.

Usage

nvim-jdtls extends the capabilities of the built-in LSP support in Neovim, so all the functions mentioned in :help lsp will work.

nvim-jdtls provides some extras, for those you'll want to create additional mappings:

nnoremap <A-o> <Cmd>lua require'jdtls'.organize_imports()<CR>
nnoremap crv <Cmd>lua require('jdtls').extract_variable()<CR>
vnoremap crv <Esc><Cmd>lua require('jdtls').extract_variable(true)<CR>
nnoremap crc <Cmd>lua require('jdtls').extract_constant()<CR>
vnoremap crc <Esc><Cmd>lua require('jdtls').extract_constant(true)<CR>
vnoremap crm <Esc><Cmd>lua require('jdtls').extract_method(true)<CR>


" If using nvim-dap
" This requires java-debug and vscode-java-test bundles, see install steps in this README further below.
nnoremap <leader>df <Cmd>lua require'jdtls'.test_class()<CR>
nnoremap <leader>dn <Cmd>lua require'jdtls'.test_nearest_method()<CR>

nvim-jdtls also adds several commands if the server starts up correctly:

  • JdtCompile
  • JdtSetRuntime
  • JdtUpdateConfig
  • JdtUpdateDebugConfig (if dap and java-debug bundles are available)
  • JdtUpdateHotcode (if dap and java-debug bundles are available)
  • JdtBytecode
  • JdtJol
  • JdtJshell
  • JdtRestart

API Reference

See :help jdtls

Debugger (via nvim-dap)

nvim-jdtls provides integration with nvim-dap.

Once setup correctly, it enables the following additional functionality:

  1. Debug applications via explicit configurations
  2. Debug automatically discovered main classes
  3. Debug junit tests. Either whole classes or individual test methods

For 1 & 2 to work, eclipse.jdt.ls needs to load the java-debug extension. For 3 to work, it also needs to load the vscode-java-test extension.

For usage instructions once installed, read the nvim-dap help. Debugging junit test classes or methods will be possible via these two functions:

require'jdtls'.test_class()
require'jdtls'.test_nearest_method()

java-debug installation

  • Clone java-debug
  • Navigate into the cloned repository (cd java-debug)
  • Run ./mvnw clean install
  • Set or extend the initializationOptions (= init_options of the config from configuration) as follows:
config['init_options'] = {
  bundles = {
    vim.fn.glob("path/to/java-debug/com.microsoft.java.debug.plugin/target/com.microsoft.java.debug.plugin-*.jar", 1)
  };
}

nvim-dap setup

nvim-jdtls will automatically register a java debug adapter with nvim-dap, if nvim-dap is available.

If you're using a plugin manager with explicit dependency manager, make sure that nvim-dap is listed as dependency for nvim-jdtls for this to work.

nvim-dap configuration

nvim-jdtls includes functionality to discover main classes and create nvim-dap configuration entries for them.

To discover the main classes you have to call require('jdtls.dap').setup_dap_main_class_configs() or use the JdtUpdateDebugConfigs command. It will only discover classes once eclipse.jdt.ls fully loaded the project. Depending on the project that may take a while. Because of that, calling require('jdtls.dap').setup_dap_main_class_configs() as part of an on_attach handler may not work well.

For manual configuration see nvim-dap Adapter Installation Wiki.

To get an overview of all available attach and launch options, take a look at java-debug options. Keep in mind that any java.debug options are settings of the vscode-java client extension and not understood by the debug-adapter itself.

vscode-java-test installation

To be able to debug junit tests, it is necessary to install the bundles from vscode-java-test:

  • Clone the repository
  • Navigate into the folder (cd vscode-java-test)
  • Run npm install
  • Run npm run build-plugin
  • Extend the bundles in the nvim-jdtls config:
-- This bundles definition is the same as in the previous section (java-debug installation)
local bundles = {
  vim.fn.glob("path/to/java-debug/com.microsoft.java.debug.plugin/target/com.microsoft.java.debug.plugin-*.jar", 1),
};

-- This is the new part
vim.list_extend(bundles, vim.split(vim.fn.glob("/path/to/microsoft/vscode-java-test/server/*.jar", 1), "\n"))
config['init_options'] = {
  bundles = bundles;
}

Troubleshooting

The client exits with an error / eclipse.jdt.ls stopped working

This can have two reasons:

  1. Your cmd definition in the Configuration is wrong.

  • Check the log files. Use :JdtShowLogs or open the log file manually. :lua print(vim.fn.stdpath('cache')) lists the path, there should be a lsp.log. You may have to increase the log level. See :help vim.lsp.set_log_level().

  • Ensure you can start the language server standalone by invoking the cmd defined in the configuration manually within a terminal.

  1. The data folder got corrupted.

Wipe the folder and ensure that it is in a dedicated directory and not within your project repository. See data directory configuration. You can use :JdtWipeDataAndRestart to do this.

Nothing happens when opening a Java file and I can't use any vim.lsp.buf functions

This can have several reasons:

  1. You didn't follow Configuration closely and aren't invoking require('jdtls').start_or_attach(config) as part of a java filetype event. Go back to the configuration section and follow it closely.

  2. You made a mistake in your configuration and there is a failure happening when you open the file. Try :set ft=java and look at the :messages output.

  3. eclipse.jdt.ls is starting but it cannot recognize your project, or it cannot import it properly. Try running :JdtCompile full or :lua require('jdtls').compile('full'). It should open the quickfix list with errors if eclipse.jdt.ls started but cannot handle your project.

Check the log files. Use :JdtShowLogs or open the log file manually. :lua print(vim.fn.stdpath('cache')) lists the path, there should be a lsp.log. You may have to increase the log level. See :help vim.lsp.set_log_level().

Error: Unable to access jarfile

Either the file doesn't exist or you're using ~ characters in your path. Neovim doesn't automatically expand ~ characters in the cmd definition. You either need to write them out or wrap the fragments in vim.fn.expand calls.

Unrecognized option: --add-modules=ALL-SYSTEM

Eclipse.jdt.ls requires at least Java 17. You're using a lower version.

is a non-project file, only syntax errors are reported

You're opening a single file without having a Gradle or Maven project. You need to use Gradle or Maven for the full functionality.

Java XY language features are not available

You need to set the language level via the Gradle or Maven configuration.

If you're starting eclipse.jdt.ls with a Java version that's different from the one the project uses, you need to configure the available Java runtimes. Add them to the config from the configuration section:

local config = {
  ..., -- not valid Lua, this is a placeholder for your other properties.
  settings = {
    java = {
      configuration = {
        -- See https://github.com/eclipse/eclipse.jdt.ls/wiki/Running-the-JAVA-LS-server-from-the-command-line#initialize-request
        -- And search for `interface RuntimeOption`
        -- The `name` is NOT arbitrary, but must match one of the elements from `enum ExecutionEnvironment` in the link above
        runtimes = {
          {
            name = "JavaSE-11",
            path = "/usr/lib/jvm/java-11-openjdk/",
          },
          {
            name = "JavaSE-17",
            path = "/usr/lib/jvm/java-17-openjdk/",
          },
        }
      }
    }
  }
}

You can also change the language level at runtime using the :JdtSetRuntime command.

Diagnostics and completion suggestions are slow

Completion requests can be quite expensive on big projects. If you're using some kind of auto-completion plugin that triggers completion requests automatically, consider deactivating it or tuning it so it is less aggressive. Triggering a completion request on each typed character is likely overloading eclipse.jdt.ls.

Newly added dependencies are not found

You can try running :JdtUpdateConfig to refresh the configuration. If that doesn't work you'll need to restart the language server.

Language server doesn't find classes that should be there

The language server supports gradle and maven as build tools. Your project should either have a pom.xml or settings.gradle and build.gradle file to declare the dependencies.

As an alternative you could manually specify the dependencies within your nvim-jdtls configuration like the following, but this is not recommended.

config.settings = {
    java = {
      project = {
        referencedLibraries = {
          '/path/to/dependencyA.jar',
          '/path/to/dependencyB.jar',
        },
      }
    }
  }

If you modify files outside of Neovim (for example with a git checkout), the language client and language server may not detect these changes and the state of the file on disk diverges with the mental model of the language server. If that happens, you need to open all changed files within Neovim and reload them with :e! to synchronize the state.

Indentation settings from eclipse formatting configuration are not recognized

This is expected. The Neovim shiftwidth and tabstop settings have a higher priority.