You need to enable debugging on the server before you can debug your WD application. You can do the enabling steps from within a special server view within the Developer Studio.
The server is running and you have specified where it is installed under Window → Preferences →SAP AS Java.
1. Choose Window → Open Perspective → Other... followed by SAP Management Console.
2. Select the relevant server node and navigate to AS Java → Process Table. The SAP Management Console (Results) view is displayed as shown in the screenshot below.
3. Select the server, open the context menu and choose Start Debug Session….
4. To log on to the relevant SAP System, enter user name and password.