microsoft / microsoft/vscode-java-debug
Unable to debug Java Card Applet Code using Java Card Simulator.
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Description
I am trying to debug a Java Card Project in VS Code, but the breakpoints are not hit.
Environment
- Operating System: Windows 10.
- JDK version: 17.0.5 LTS
- Visual Studio Code version: 1.74.2
- Java extension version:
- Java Debugger extension version: 0.47.2022112823
Steps To Reproduce

- Download and Install Java Card Simulator from Oracle. [Java Card Classic Development Kit 3.0.5u4]
• https://www.oracle.com/java/technologies/java-archive-downloads-javame-downloads.html#javacardkitv305 - Download and Extract Sample Java Card Project. [Sample.zip attached.]
- Terminal 1: Start the Simulator.
•cd "{Your_Install_Location}\Java Card Development Kit 3.0.5u4\bin}"
•cref_tdual.exe -p 9025 -debugPort 7019 - Terminal 2: Launch APDU Tool.
•cd "{Your_Install_Location}\Java Card Development Kit 3.0.5u4\bin}"
•apdutool.bat -p 9025 - Load the cap file in Simulator.
• Copy paste the contents of {Your_Extract_Location}/apdu_scripts/cap-com.sample.script in Terminal-2 and press Enter - Installing the application in Simulator.
• Copy paste the contents of {Your_Extract_Location}/apdu_scripts/create-com.sample.MyApplet.script in Terminal-2 and press Enter. - Terminal 3: Launch Debug Proxy.
•cd "{Your_Install_Location}\Java Card Development Kit 3.0.5u4\lib"
•java -jar jc-debug-proxy.jar -port 8989 -vmPort 7019 -capPath {Your_Extract_Location}\Sample\deliverables\com\sample\javacard\sample.cap
---- Debugging In VS Code [Doesn't work]-----
- Open the Sample project in VS Code.
- Start the debug session in VS Code.(Press F5). [A launch.json with correct configurations is already present.]
- Open the file src/com/sample/MyApplet.java and set a breakpoint at line 57.
- In Terminal-2
•0x00 0xA4 0x04 0x00 0x06 0x89 0x89 0x89 0x89 0x89 0x81 0x7F;
• Press Enter.
• The breakpoint at Line-57 should be hit. [This doesn't work.]
---- Debugging with Eclipse for Java [Working] ----------
- Open the Sample project in Eclipse.
- Select File -> Open Projects From File System -> Select the Sample Directory.
- Setup Debug Configuration.
• Select Run -> Debug Configurations...
• On Left Panel Select Remote Java Application.
• In Project Field, Click on Browse and Select Sample.
• Change the port to 8989
• Click on Apply then Debug. - Open the file src/com/sample/MyApplet.java and set a breakpoint at line 57.
- In Terminal-2
•0x00 0xA4 0x04 0x00 0x06 0x89 0x89 0x89 0x89 0x89 0x81 0x7F;
• Press Enter.
• The breakpoint at Line-57 should be hit. [Working]
Additional Informations
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start by reproducing the breakpoint failure with the Java Card Simulator, Debug Proxy, APDU Tool, and the provided Sample project; compare the VS Code F5 session with the working Eclipse remote-debug session on port 8989. Inspect the existing launch.json and the breakpoint at src/com/sample/MyApplet.java:57. Done means the APDU command consistently stops at that breakpoint in VS Code.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- java, vscode
- Domain
- developer-experience, devtools
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 38/100