Maven Debug Launches Two Processes In VS Code: A Fix

Nov 25, 2025 by Alex Johnson 53 views

Are you experiencing an issue where Maven launches two processes when debugging in VS Code? You're not alone! Since version 0.45.0, some users have reported this bug, where one process runs in debug mode and another in normal mode. This can be particularly problematic with tasks like jetty:run, where the debug process fails because the port is already in use. Let’s dive into this issue, explore the causes, and discuss potential solutions.

Understanding the Issue of Maven Debug

The core problem is that when you initiate a debug session for a Maven task in VS Code, two Java processes are launched instead of one. One process starts with the debugger attached, while the other runs without debugging. This unexpected behavior can lead to various issues, especially when the task involves binding to specific ports or resources.

Why This Happens

While the exact root cause might vary depending on the setup, the issue seems to stem from changes introduced in version 0.45.0 of the VS Code Maven extension. The extension might be inadvertently triggering two separate executions of the Maven task – one for debugging and another for regular execution. This could be due to how the extension handles the lifecycle phases or the way it interacts with the Maven command-line interface.

Impact on Development

The dual-process launch can significantly hinder development workflows. For instance, when using jetty:run, the first process claims the designated port (e.g., 8080), preventing the debug process from binding to it. This results in the debugger failing to attach, making it impossible to debug the application effectively. Moreover, the extra process consumes system resources, potentially slowing down the development environment. This is a significant issue for developers who rely on debugging to identify and fix issues in their code.

Diagnosing the Double Process Issue

To effectively tackle this problem, it's crucial to diagnose it correctly. Here’s a step-by-step guide to help you identify if you're experiencing this issue:

Steps to Reproduce

Open your Maven project in VS Code.
Navigate to the Maven panel in the VS Code activity bar.
Locate the task you want to debug (e.g., jetty:run).
Right-click on the task and select "Debug".
Observe the console output and process list.

Identifying the Processes

After initiating the debug session, check your system's process list (Task Manager on Windows, Activity Monitor on macOS, or ps command on Linux) to see if two Java processes have been launched. The command-line arguments for each process can provide clues about their purpose.

Debug Process: This process will typically include debugging-related JVM arguments, such as -Xdebug and -Xrunjdwp. These arguments configure the Java Virtual Machine to listen for a debugger connection.
Normal Process: This process will lack the debugging arguments and run the Maven task in standard mode.

Examining the Output

Check the VS Code output panel for any error messages or unusual behavior. If the debug process fails to start due to a port conflict (e.g., “Address already in use”), it’s a strong indication of the dual-process issue. The output logs may also show that the task was executed twice, further confirming the problem.

Workarounds and Solutions for Debugging Maven

While the root cause of the dual-process issue might require a fix from the VS Code Maven extension team, several workarounds and solutions can help you continue debugging your Maven projects effectively.

Downgrade the Extension

One of the quickest solutions is to revert to a previous version of the VS Code Maven extension where this issue wasn't present. Version 0.44.0 is known to work correctly. To downgrade:

Go to the Extensions view in VS Code (Ctrl+Shift+X or Cmd+Shift+X).
Find the "Maven for Java" extension.
Click the dropdown arrow next to the "Uninstall" button.
Select "Install Another Version...".
Choose version 0.44.0 from the list.

This workaround helps bypass the bug introduced in later versions, allowing you to debug your Maven tasks as expected.

Use Remote Debugging

Another approach is to configure remote debugging. This involves starting your Maven application in debug mode from the command line and then attaching the VS Code debugger to the running process. This method gives you more control over the debugging process and avoids the dual-process issue.

Start your Maven task with the debug arguments. For example, in your pom.xml file, you can add the following configuration to the maven-surefire-plugin or maven-failsafe-plugin:
```
<configuration>
  <argLine>
    -agentlib:jdwp=transport=dt_socket,server=y,suspend=n,address=5005
  </argLine>
</configuration>
```
This configuration sets up the JVM to listen for a debugger connection on port 5005. You can then run your task from the command line using mvnDebug <your-task> (e.g., mvnDebug jetty:run).

In VS Code, create a new debug configuration in your launch.json file:

{
  "version": "0.2.0",
  "configurations": [
    {
      "type": "java",
      "name": "Attach to Remote Debugger",
      "request": "attach",
      "hostName": "localhost",
      "port": 5005
    }
  ]
}

Start your Maven task from the command line using the mvnDebug command.
Run the "Attach to Remote Debugger" configuration in VS Code. This will connect the VS Code debugger to the running Maven process.

By using remote debugging, you can sidestep the issue of the extension launching two processes and still debug your application effectively.

Configure Maven Tasks Directly

Instead of relying on the VS Code Maven extension to launch the debug process, you can configure Maven tasks directly in your launch.json file. This allows you to specify the exact command-line arguments and avoid any potential conflicts caused by the extension.

Open your project's .vscode/launch.json file.

Add a new configuration for your Maven task. For example:

{
  "version": "0.2.0",
  "configurations": [
    {
      "type": "java",
      "name": "Maven Jetty Run Debug",
      "request": "launch",
      "cwd": "${workspaceFolder}",
      "console": "internalConsole",
      "mainClass": "org.codehaus.plexus.classworlds.launcher.Launcher",
      "args": ["jetty:run"],
      "vmArgs": "-Xdebug -Xrunjdwp:transport=dt_socket,server=y,suspend=y,address=5005",
      "env": {
        "MAVEN_HOME": "${env:MAVEN_HOME}"
      }
    }
  ]
}

This configuration specifies the main class for the Maven launcher, the arguments for the jetty:run task, and the necessary JVM arguments for debugging. By setting the vmArgs, you ensure that the task runs in debug mode without relying on the extension's default behavior.

Run this configuration from the VS Code debug panel. This will launch the Maven task with the specified debug settings, avoiding the dual-process issue.

Reporting the Issue and Staying Updated

If you encounter this bug, it’s crucial to report it to the VS Code Maven extension team. This helps them understand the scope of the problem and prioritize a fix. You can report the issue on the extension’s GitHub repository or through the VS Code marketplace.

Providing Detailed Information

When reporting the issue, include as much detail as possible. This should include:

VS Code version
Maven extension version
Operating system
Steps to reproduce the issue
Console output and process list screenshots
Any relevant configurations or settings

The more information you provide, the easier it will be for the developers to diagnose and fix the problem.

Monitoring for Updates

Keep an eye on the VS Code Maven extension’s release notes and issue tracker for updates. The developers may release a fix in a future version. Regularly updating your extensions ensures you have the latest features and bug fixes.

Conclusion on Debugging Maven in VS Code

The issue of Maven launching two processes in debug mode in VS Code can be a frustrating obstacle for developers. However, by understanding the problem, diagnosing it effectively, and implementing the workarounds discussed, you can continue to debug your Maven projects with minimal disruption. Whether it's downgrading the extension, using remote debugging, or configuring Maven tasks directly, there are several ways to overcome this challenge. Remember to report the issue and stay updated on the extension's progress to ensure a smoother development experience.

By staying informed and proactive, you can maintain an efficient development workflow even when encountering unexpected bugs. Happy debugging!

For more information on debugging Java applications, you can visit the official Eclipse Foundation website, which provides comprehensive resources and documentation on Java development tools.