coc-java-debug

An extension for coc.nvim to enable the Java Debug Server extension for the jdt.ls language server that is loaded by coc-java.

Disclaimer

This project is intended to provide the simplest possible integration between Vimspector and jdt.ls. A minimal amount of manual configuration is required on first setup.

Note, this began as an experiment, but generally "works for me". Your mileage may vary.

Prerequisites

Be sure to have the coc-java extension installed.

:CocInstall coc-java

You will also need to install the Vimspector plugin for Vim.

Install

:CocInstall coc-java-debug

Uninstall

:CocUninstall coc-java-debug

Features

• Integration with Vimspector
• Provide a simple command to launch Vimspector and connect the Java debugger.

Available commands

The following CocCommand options are provided:

• java.debug.vimspector.start: Launch Vimspector and connect it to the Java Debug Server.

Command Arguments

Optionally, java.debug.vimspector.start will accept a JSON string of settings which will be passed to Vimspector via "LaunchWithSettings".

You may use this feature to override values in your .vimspector.json file at runtime.

For example, here's how you could call it from within Vim with custom settings:

:CocCommand java.debug.vimspector.start {"configuration":"Run Test","Test":"Name of the test"}

These settings will take precedence when launching Vimspector.

Supported settings

The following settings are supported in CocConfig:

• java.debug.vimspector.profile : (Deprecated) Set to null and use "default":true in Vimspector.json instead. Specifies the Vimspector profile to activate when launching. Set to null to be prompted if multiple configurations are found and no default is set. Defaults to Java Attach
• java.debug.vimspector.substitution.adapterPort : Specifies the Vimspector adapter port substitution name in .vimspector.json. The actual port number will replace this value in the Vimspector config when the debug server is started. Defaults to AdapterPort

Usage and Setup

This example will use Vimspector as the user interface for interacting with the Java Debug Server from within Vim.

It will demonstrate attaching to a Java program that is running with remote debugging enabled.

Setup Vimspector

Install the Vimspector plugin for Vim.

Add a .vimspector.json file in the root directory of your Java project with the following contents. Note, don't change "${AdapterPort}". See issue #3 for an explanation of how this port value works.

{
  "adapters": {
    "java-debug-server": {
      "name": "vscode-java",
      "port": "${AdapterPort}"
    }
  },
  "configurations": {
    "Java Attach": {
      "default": true,
      "adapter": "java-debug-server",
      "configuration": {
        "request": "attach",
        "host": "127.0.0.1",
        "port": "5005"
      },
      "breakpoints": {
        "exception": {
          "caught": "N",
          "uncaught": "N"
        }
      }
    }
  }
}

Review the Vimspector config docs for what's possible within this file.

Configure Vim

This extension provides :CocCommand java.debug.vimspector.start to simplify launching Vimspector.

Note, it does not start your Java process in debug mode. An example of this is covered below.

Add the following config to your ~/.vimrc file or wherever appropriate for your Vim setup to further simplify launching Vimspector.

" Press F1 key to lanuch Vimspector
nmap <F1> :CocCommand java.debug.vimspector.start<CR>

Alternative Configuration (Optional)

If you'd prefer to launch the Vimspector plugin directly with your own configuration then add something similar the following config to your ~/.vimrc file or wherever appropriate for your Vim setup.

Note, this will bypass using the :CocCommand documented above to start the debug session.

function! JavaStartDebugCallback(err, port)
  execute "cexpr! 'Java debug started on port: " . a:port . "'"
  call vimspector#LaunchWithSettings({ "configuration": "Java Attach", "AdapterPort": a:port })
endfunction

function JavaStartDebug()
  call CocActionAsync('runCommand', 'vscode.java.startDebugSession', function('JavaStartDebugCallback'))
endfunction

nmap <F1> :call JavaStartDebug()<CR>

This example provides a way to start the Java debug server through coc.vim and then tell Vimspector which port to use to connect to the debug server. It maps the F1 key to kick things off, but you can change this key mapping to whatever you want.

Start the debug session

First, run a Java program with remote debugging enabled. Be sure it is configured to pause and wait for a remote connection on port 5005 for this example work.

For a simple Java program. Create a Hello.java file with these contents.

public class Hello {
  public static void main(String[] args) {
    System.out.println("Hello World!");
  }
}

Next, run these commands from a shell to compile the program and then start it with remote debugging enabled.

javac -g Hello.java
java -Xdebug -Xrunjdwp:server=y,transport=dt_socket,address=5005,suspend=y Hello

Alternatively, you may use Maven for this step remote debugging Maven tests.

mvn test -Dmaven.surefire.debug

If everything works correctly you will see this message.

Listening for transport dt_socket at address: 5005

Now, open the file you want to debug in Vim and set a breakpoint with Vimspector.

Finally, start the debug session in Vim by pressing your F1 key or use your custom key mapping if you have altered the config from this example. This should result in Vimspector opening in a new tab in Vim with your Java program paused at the breakpoint you set.

That's it! You may now step debug your way through a Java program from within Vim.

Note, if you use a Java debug port different than 5005 you will need to change that value in your .vimspector.json file. It is also possible to configure this port dynamically in Vimspector in the same manner as the debug adapter port.

License

EPL 2.0, See LICENSE for more information.