The JVM can be started in debug mode and can be attached to a JPDA (Java Platform Debugger Architecture) debugger. When you enable debugging, you enable both local and remote debugging.
Sun Java System Web Server's debugging is based on JPDA software. To enable debugging, perform the following tasks.
Click the Configurations tab to see the list of available configurations and select the configuration you need.
Click Java > JVM Settings tab.
Under Debug Java Settings, select the Enable Debug checkbox.
Provide JVM options as necessary by clicking the New button.
The default JPDA options are as follows:
If you substitute suspend=y, the JVM starts in suspended mode and stays suspended until a debugger attaches to it. This is helpful if you want to start debugging as soon as the JVM starts. To specify the port to use when attaching the JVM to a debugger, specify address=port_number. Check out the JPDA documentation for a list of debugging options.