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coc-java-debug

An extension for coc.nvim to enable the Java Debug Server for the Java language server (jdt.ls) in Vim/Neovim.

It also provides an easy way to launch Vimspector and connect it to the Java debug server.

Features

  • Integration with Vimspector.
  • Launch Vimspector and connect to the Java debugger with a single command.
  • Provide Vimspector config substitutions for the following Java project values:
    • class paths
    • main class
    • module paths
    • project name
  • Configure Java debug settings.

Requirements

Quick Start

Install the coc-java-debug extension.

:CocInstall coc-java-debug

Open a Java file with a main method in Vim.

Set a breakpoint in your main method.

Execute this Vim command.

:CocCommand java.debug.vimspector.start

Goals

  • Provide a simple integration between Vimspector and the Java Debug Server.
  • Provide Java-specific replacements for Vimspector's native config.
    • See java.debug.vimspector.substitution.* settings.
  • Support Vim and Neovim.

Non-Goals

Available commands

The following :CocCommand options are provided:

  • java.debug.vimspector.start: Launch Vimspector and connect it to the Java Debug Server.
  • java.debug.settings.update: Sync local debug settings to Java Debug Server. Done automatically when Vimspector is started with java.debug.vimspector.start command.

Command Arguments

java.debug.vimspector.start

  • Optionally accepts a JSON string of settings to be passed to Vimspector using "LaunchWithSettings" internally.
  • This feature may be used to override values in the Vimspector config at runtime.
  • For example, it can be used to specify which configuration to load and a replacement value.
:CocCommand java.debug.vimspector.start {"configuration":"Run Test","Test":"Name of the test"}

Supported settings

The following settings are supported in CocConfig:

java.debug.vimspector

  • java.debug.vimspector.config.createIfNotExists : If true then a .vimspector.json config will be created in the workspace if one doesn't already exist, defaults to true.
  • java.debug.vimspector.substitution.adapterPort : Specifies the adapter port substitution name for use in .vimspector.json. The actual port number will replace this value in the config when the debug server is started, defaults to AdapterPort.
  • java.debug.vimspector.substitution.classPaths : Specifies the 'class paths' substitution name for use in .vimspector.json. The actual class paths will replace this value in the Vimspector config, defaults to ClassPaths.
  • java.debug.vimspector.substitution.mainClass : Specifies the 'main class' substitution name for use in .vimspector.json. The actual main class will replace this value in the Vimspector config, defaults to MainClass.
  • java.debug.vimspector.substitution.modulePaths : Specifies the 'module paths' substitution name for use in .vimspector.json. The actual module paths will replace this value in the Vimspector config, defaults to ModulePaths.
  • java.debug.vimspector.substitution.projectName : Specifies the 'project name' substitution name for use in .vimspector.json. The actual project name will replace this value in the Vimspector config, defaults to ProjectName.

java.debug.settings

  • java.debug.logLevel: minimum level of debugger logs that are sent to language server, defaults to warn.
  • java.debug.settings.showHex: show numbers in hex format in "Variables" viewlet, defaults to false.
  • java.debug.settings.showStaticVariables: show static variables in "Variables" viewlet, defaults to false.
  • java.debug.settings.showQualifiedNames: show fully qualified class names in "Variables" viewlet, defaults to false.
  • java.debug.settings.showLogicalStructure: show the logical structure for the Collection and Map classes in "Variables" viewlet, defaults to true.
  • java.debug.settings.showToString: show 'toString()' value for all classes that override 'toString' method in "Variables" viewlet, defaults to true.
  • java.debug.settings.maxStringLength: the maximum length of string displayed in "Variables" viewlet, the string longer than this length will be trimmed, defaults to 0 which means no trim is performed.
  • java.debug.settings.numericPrecision: the precision when formatting doubles in "Variables" viewlet.
  • java.debug.settings.hotCodeReplace: Reload the changed Java classes during debugging, defaults to manual.
  • java.debug.settings.exceptionBreakpoint.exceptionTypes: Specifies a set of exception types you want to break on, e.g. java.lang.NullPointerException. A specific exception type and its subclasses can be selected for caught exceptions, uncaught exceptions, or both can be selected.
  • java.debug.settings.exceptionBreakpoint.allowClasses: Specifies the allowed locations where the exception breakpoint can break on. Wildcard is supported, e.g. java.*, *.Foo.
  • java.debug.settings.exceptionBreakpoint.skipClasses: Skip the specified classes when breaking on exception.
    • $JDK - Skip the JDK classes from the default system bootstrap classpath, such as rt.jar, jrt-fs.jar.
    • $Libraries - Skip the classes from application libraries, such as Maven, Gradle dependencies.
    • java.* - Skip the specified classes. Wildcard is supported.
    • java.lang.ClassLoader - Skip the classloaders.
  • java.debug.settings.stepping.skipClasses: Skip the specified classes when stepping.
    • $JDK - Skip the JDK classes from the default system bootstrap classpath, such as rt.jar, jrt-fs.jar.
    • $Libraries - Skip the classes from application libraries, such as Maven, Gradle dependencies.
    • java.* - Skip the specified classes. Wildcard is supported.
    • java.lang.ClassLoader - Skip the classloaders.
  • java.debug.settings.stepping.skipSynthetics: Skip synthetic methods when stepping.
  • java.debug.settings.stepping.skipStaticInitializers: Skip static initializer methods when stepping.
  • java.debug.settings.stepping.skipConstructors: Skip constructor methods when stepping.
  • java.debug.settings.jdwp.limitOfVariablesPerJdwpRequest: The maximum number of variables or fields that can be requested in one JDWP request. The higher the value, the less frequently debuggee will be requested when expanding the variable view. Also a large number can cause JDWP request timeout. Defaults to 100.
  • java.debug.settings.jdwp.requestTimeout: The timeout (ms) of JDWP request when the debugger communicates with the target JVM. Defaults to 3000.
  • java.debug.settings.jdwp.async: Experimental: Controls whether the debugger is allowed to send JDWP commands asynchronously. Async mode can improve remote debugging response speed on high-latency networks. Defaults to auto, and automatically switch to async mode when the latency of a single jdwp request exceeds 15ms during attach debugging.
    • auto (Default)
    • on
    • off
  • java.debug.settings.debugSupportOnDecompiledSource: [Experimental]: Enable debugging support on the decompiled source code. Be aware that this feature may affect the loading speed of Call Stack Viewlet. You also need Language Support for Java by Red Hat@1.20.0 or higher to use this feature.

Usage and Setup

Debug a Main Method

This example will demonstrate how to load a Java program with a main method and debug it using Vimspector.

If you don't have a .vimspector.json file in the root directory of your Java project then coc-java-debug will create one for you unless java.debug.vimspector.config.createIfNotExists is disabled.

If you already have a .vimspector.json file then add the config below.

{
  "adapters": {
    "coc-java-debug": {
      "port": "${AdapterPort}"
    }
  },
  "configurations": {
    "javaLaunch": {
      "default": true,
      "adapter": "coc-java-debug",
      "configuration": {
        "args": "${args}",
        "request": "launch",
        "projectName": "${ProjectName}",
        "mainClass": "${MainClass}",
        "classPaths": ["*${ClassPaths}"]
      },
      "breakpoints": {
        "exception": {
          "caught": "N",
          "uncaught": "N"
        }
      }
    }
  }
}

Next, open a Java file with a main method in Vim and set a breakpoint in your main method.

Execute the command to start debugging.

:CocCommand java.debug.vimspector.start

You will be prompted with

Enter value for args:

If you don't have any program arguments just press your enter key. Otherwise, type in your args just as you would from a terminal and then press your enter key.

At this point Vimspector should open and pause your Java program on the breakpoint you set.

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

Remote Debugging

This example will demonstrate attaching to a Java program that is running with remote debugging enabled. This is useful for debugging tests or running services.

Vimspector Attach Config

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

{
  "adapters": {
    "coc-java-debug": {
      "port": "${AdapterPort}"
    }
  },
  "configurations": {
    "javaAttach": {
      "default": true,
      "adapter": "coc-java-debug",
      "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 remote debug mode. An example of how to do that is covered below.

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

" Press F1 key to launch Vimspector
nmap <F1> :CocCommand java.debug.vimspector.start<CR>
Start the Remote 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

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.

Also note, if you use Maven for builds you may start remote debugging for tests and then run Vimspector.

mvn test -Dmaven.surefire.debug
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.

License

EPL 2.0, See LICENSE for more information.