Question
Answer and Explanation
To run standalone Tomcat 11 in debug mode, you will need to configure the startup process to enable remote debugging. This allows you to attach a Java debugger, such as those included in IntelliJ IDEA or Eclipse, to the Tomcat server for inspecting application execution.
Here are the detailed steps:
1. Locate the Tomcat Startup Scripts:
- Navigate to the `bin` directory within your Tomcat 11 installation. You'll find scripts such as `catalina.sh` (for Linux/macOS) or `catalina.bat` (for Windows).
2. Modify the Startup Script:
- Edit the appropriate script. You will need to add JVM debug options to enable remote debugging. The most common approach is to set the `JPDA_ADDRESS` environment variable and enable the Java Platform Debugger Architecture (JPDA).
- For Linux/macOS (catalina.sh): Open `catalina.sh` in a text editor and add the following line before the line that starts with `exec "$PRGDIR"/"$EXECUTABLE" ...`:
export JPDA_ADDRESS="8000"
export JPDA_TRANSPORT="dt_socket"
- Also, modify the line containing the exec command as follows:
exec "$PRGDIR"/"$EXECUTABLE" jpda start "$@"
- For Windows (catalina.bat): Open `catalina.bat` in a text editor and add the following lines before the line that starts with `"%_EXECJAVA%" ...`:
set JPDA_ADDRESS=8000
set JPDA_TRANSPORT=dt_socket
- Also, modify the line containing the exec command as follows:
"%_EXECJAVA%" jpda start %CMD_LINE_ARGS%
3. Explanation of the Settings:
- `JPDA_ADDRESS`: This specifies the port on which the debugger will connect. `8000` is a commonly used port, but you can choose a different one if needed.
- `JPDA_TRANSPORT`: This sets the transport protocol used for debugging, which is typically `dt_socket`.
4. Start Tomcat in Debug Mode:
- Now, start Tomcat using the `startup.sh` (Linux/macOS) or `startup.bat` (Windows) script from the `bin` directory. This will start Tomcat with the debug settings you configured.
- Example:
./startup.sh (Linux/macOS)
startup.bat (Windows)
5. Attach a Java Debugger:
- Open your IDE (IntelliJ IDEA, Eclipse, etc.) and create a new "Remote Debug" configuration.
- Configure the debugger to use:
- The correct hostname (usually `localhost` if Tomcat is running on your machine).
- The port number you specified in `JPDA_ADDRESS` (e.g., `8000`).
- The transport as `dt_socket`.
- Start the debugger in your IDE. It should connect to the Tomcat instance, and you can then set breakpoints and debug your applications as required.
6. Verifying the Setup:
- Check the Tomcat console logs for lines indicating the debug listener has started. In the Tomcat log it will output something similar to: `Listening for transport dt_socket at address: 8000`
By following these steps, you'll have Tomcat 11 running in debug mode, allowing you to debug your Java web applications effectively. Remember to stop the debug mode and remove the changes to the startup scripts when not needed to prevent unnecessary resources consumption and security risks.