java-launch-troubleshooting

Apps & Automation

Use when the user wants to run, launch, start, restart, or stop a Java program (main class, Spring Boot, JAR, Maven, Gradle), or diagnose launch failures (mainClass missing, classpath unresolved, compile failure, "project not detected", `ClassNotFoundException` at startup). NOT for inspecting variables, stepping, or setting breakpoints in an already-running debug session — use `java-debug-inspection` for that.

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How to use this skill

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I want to install this Agent Skill for this project in Codex.

Source SKILL.md: https://github.com/microsoft/vscode-java-debug/blob/HEAD/resources/skills/java-launch-troubleshooting/SKILL.md

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First, summarize what it does, its dependencies, license status if identifiable, and any risks. Show the exact files you propose to add under .agents/skills/java-launch-troubleshooting/. Do not write files or run scripts until I approve.

After I approve, install the complete skill folder, including required referenced files, into that project location. Verify it is discoverable, then tell me its actual invocation name and how to use it. Do not claim it is installed until you have verified it.

Copying this prompt does not install or run the skill. Review third-party files before use. Codex skill guide

Java Launch Troubleshooting

Use this skill when the user wants to start or stop a Java program, or when an attempted launch fails. Typical user phrases:

"run this main class", "start the app", "launch the Spring Boot project", "run the jar"
"stop the debug session", "kill the running app"
prior run_in_terminal failed with ClassNotFoundException, mainClass is not set, Could not find or load main class, Could not resolve classpath
the user changed pom.xml / build.gradle and the app no longer starts

Tools

These language model tools are contributed by the Debugger for Java extension and are deferred. Activate them with tool_search_tool_regex using pattern java_breakpoint|debug before first use.

Tool	Purpose
`debug_java_application`	Build + resolve classpath + start JVM. Returns precise compile and classpath errors.
`get_debug_session_info`	Check whether a debug session is already running and its status.
`stop_debug_session`	Stop a running Java debug session cleanly.

Preferred Workflow

Confirm intent. Is the user trying to run / start / launch / stop a Java program (use this skill) or just edit code (do not load this skill)?
Check existing session. Call get_debug_session_info first. If a session is already running for the target, do not launch a second one.
Launch. Call debug_java_application with target = the fully qualified main class or JAR, and workspacePath = the project root containing pom.xml, build.gradle, or .classpath. Let skipBuild default to false so the tool handles compilation.
Read the error. If debug_java_application fails, the error message is structured (mainClass missing, classpath unresolved, build failure with line number). Use it to suggest a fix — do not retry with run_in_terminal.
Stop when done. When the user says "stop", "kill it", or has the answer they need, call stop_debug_session.

Common Failure Modes

Symptom from `debug_java_application`	Likely cause	Suggested fix
`mainClass is not configured` / `mainClass missing`	Project has no `launch.json`, and the file has no `public static void main`	Ask user which class to launch, or generate `launch.json`
`Could not resolve classpath`	Maven/Gradle import has not completed, or `pom.xml` has unresolved dependencies	Wait for Java Language Server import, then ask user to run `Java: Clean Java Language Server Workspace`
`Compilation failed` with file:line	Source code has a compile error	Fix the reported error in the source file, do not retry the launch
`Project not detected`	`workspacePath` does not contain a build file	Re-check `workspacePath`; for multi-module projects, use the module root, not the repo root

When NOT to Use This Skill

The user is editing or refactoring Java code without running it → do nothing
The user is already inside a live debug session and wants to inspect variables, evaluate expressions, walk the stack, step, or set / remove breakpoints → use java-debug-inspection instead, do not re-launch
The program is a non-Java language → do not load this skill

Fallback

If debug_java_application returns Java Language Server not ready or repeats the same error twice, fall back to run_in_terminal with the appropriate mvn or gradle command and report the raw output to the user. Do not retry the debug tool more than twice.