Following are forks of original repositories pre-configured for java. If you don't know how to get started, use one of the following to get started. You can click on n commits ahead of link to see the changes made on top of the original project

• LazyVim
• Kickstart
• AstroNvim

• Install the plugin

Using lazy.nvim

return {'nvim-java/nvim-java'}

• Setup nvim-java before lspconfig

require('java').setup()

• Setup jdtls like you would usually do

require('lspconfig').jdtls.setup({})

Yep! That's all :)

• JavaBuildBuildWorkspace - Runs a full workspace build

• JavaBuildCleanWorkspace - Clear the workspace cache (for now you have to close and reopen to restart the language server after the deletion)

• JavaRunnerRunMain - Runs the application or selected main class (if there are multiple main classes)

:JavaRunnerRunMain
:JavaRunnerRunMain <arguments> <to> <pass>

• JavaRunnerStopMain - Stops the running application
• JavaRunnerToggleLogs - Toggle between show & hide runner log window

• JavaDapConfig - DAP is autoconfigured on start up, but in case you want to force configure it again, you can use this API

• JavaTestRunCurrentClass - Run the test class in the active buffer
• JavaTestDebugCurrentClass - Debug the test class in the active buffer
• JavaTestRunCurrentMethod - Run the test method on the cursor
• JavaTestDebugCurrentMethod - Debug the test method on the cursor
• JavaTestViewLastReport - Open the last test report in a popup window

• JavaProfile - Opens the profiles UI

• JavaRefactorExtractVariable - Create a variable from value at cursor/selection
• JavaRefactorExtractVariableAllOccurrence - Create a variable for all occurrences from value at cursor/selection
• JavaRefactorExtractConstant - Create a constant from the value at cursor/selection
• JavaRefactorExtractMethod - Create a method from the value at cursor/selection
• JavaRefactorExtractField - Create a field from the value at cursor/selection

• JavaSettingsChangeRuntime - Change the JDK version to another

• build.build_workspace - Runs a full workspace build

require('java').build.build_workspace()

• build.clean_workspace - Clear the workspace cache (for now you have to close and reopen to restart the language server after the deletion)

require('java').build.clean_workspace()

• built_in.run_app - Runs the application or selected main class (if there are multiple main classes)

require('java').runner.built_in.run_app({})
require('java').runner.built_in.run_app({'arguments', 'to', 'pass', 'to', 'main'})

• built_in.stop_app - Stops the running application

require('java').runner.built_in.stop_app()

• built_in.toggle_logs - Toggle between show & hide runner log window

require('java').runner.built_in.toggle_logs()

• config_dap - DAP is autoconfigured on start up, but in case you want to force configure it again, you can use this API

require('java').dap.config_dap()

• run_current_class - Run the test class in the active buffer

require('java').test.run_current_class()

• debug_current_class - Debug the test class in the active buffer

require('java').test.debug_current_class()

• run_current_method - Run the test method on the cursor

require('java').test.run_current_method()

• debug_current_method - Debug the test method on the cursor

require('java').test.debug_current_method()

• view_report - Open the last test report in a popup window

require('java').test.view_last_report()

require('java').profile.ui()

• extract_variable - Create a variable from value at cursor/selection

require('java').refactor.extract_variable()

• extract_variable_all_occurrence - Create a variable for all occurrences from value at cursor/selection

require('java').refactor.extract_variable_all_occurrence()

• extract_constant - Create a constant from the value at cursor/selection

require('java').refactor.extract_constant()

• extract_method - Create method from the value at cursor/selection

require('java').refactor.extract_method()

• extract_field - Create a field from the value at cursor/selection

require('java').refactor.extract_field()

• change_runtime - Change the JDK version to another

require('java').settings.change_runtime()

Neoconf can be used to manage LSP setting including jdtls. Neoconf allows global configuration as well as project vice configurations. Here is how you can set Jdtls setting on neoconf.json

{
  "lspconfig": {
    "jdtls": {
      "java.configuration.runtimes": [
        {
          "name": "JavaSE-21",
          "path": "/opt/jdk-21",
          "default": true
        }
      ]
    }
  }
}

Pass the settings to Jdtls setup.

require('lspconfig').jdtls.setup({
  settings = {
    java = {
      configuration = {
        runtimes = {
          {
            name = "JavaSE-21",
            path = "/opt/jdk-21",
            default = true,
          }
        }
      }
    }
  }
})

For most users changing the default configuration is not necessary. But if you want, following options are available

{
  --  list of file that exists in root of the project
  root_markers = {
    'settings.gradle',
    'settings.gradle.kts',
    'pom.xml',
    'build.gradle',
    'mvnw',
    'gradlew',
    'build.gradle',
    'build.gradle.kts',
    '.git',
  },

  -- load java test plugins
  java_test = {
    enable = true,
  },

  -- load java debugger plugins
  java_debug_adapter = {
    enable = true,
  },

  spring_boot_tools = {
    enable = true,
  },

  jdk = {
    -- install jdk using mason.nvim
    auto_install = true,
  },

  notifications = {
    -- enable 'Configuring DAP' & 'DAP configured' messages on start up
    dap = true,
  },

  -- We do multiple verifications to make sure things are in place to run this
  -- plugin
  verification = {
    -- nvim-java checks for the order of execution of following
    -- * require('java').setup()
    -- * require('lspconfig').jdtls.setup()
    -- IF they are not executed in the correct order, you will see a error
    -- notification.
    -- Set following to false to disable the notification if you know what you
    -- are doing
    invalid_order = true,

    -- nvim-java checks if the require('java').setup() is called multiple
    -- times.
    -- IF there are multiple setup calls are executed, an error will be shown
    -- Set following property value to false to disable the notification if
    -- you know what you are doing
    duplicate_setup_calls = true,

    -- nvim-java checks if nvim-java/mason-registry is added correctly to
    -- mason.nvim plugin.
    -- IF it's not registered correctly, an error will be thrown and nvim-java
    -- will stop setup
    invalid_mason_registry = true,
  },
}

Following is the high level idea. Jdtls is the language server nvim-java communicates with. However, we don't have all the features we need just in Jdtls. So, we are loading java-test & java-debug-adapter extensions when we launch Jdtls. Once the language server is started, we communicate with the language server to do stuff.

For instance, to run the current test,

• Request Jdtls for test classes
• Request Jdtls for class paths, module paths, java executable
• Request Jdtls to start a debug session and send the port of the session back
• Prepare TCP connections to listen to the test results
• Start nvim-dap and let user interactions to be handled by nvim-dap
• Parse the test results as they come in
• Once the execution is done, open a window show the test results

  ┌────────────┐                         ┌────────────┐
  │            │                         │            │
  │   Neovim   │                         │   VSCode   │
  │            │                         │            │
  └─────▲──────┘                         └──────▲─────┘
        │                                       │
        │                                       │
        │                                       │
        │                                       │
┌───────▼───────┐                ┌──────────────▼──────────────┐
│               │                │                             │
│   nvim-java   │                │   Extension Pack for Java   │
│               │                │                             │
└───────▲───────┘                └──────────────▲──────────────┘
        │                                       │
        │                                       │
        │                                       │
        │                                       │
        │                                       │
        │              ┌───────────┐            │
        │              │           │            │
        └──────────────►   JDTLS   ◄────────────┘
                       │           │
                       └───▲───▲───┘
                           │   │
                           │   │
                           │   │
                           │   │
                           │   │
  ┌───────────────┐        │   │         ┌────────────────────────┐
  │               │        │   │         │                        │
  │   java-test   ◄────────┘   └─────────►   java-debug-adapter   │
  │               │                      │                        │
  └───────────────┘                      └────────────────────────┘