One way to debug applications is to look at the server log in domain-dir/logs/server.log. The log contains output from the Application Server and your applications. You can log messages from any Java class in your application with System.out.println and the Java Logging APIs (documented at http://java.sun.com/javase/6/docs/technotes/guides/logging/index.html) and from web components with the ServletContext.log method.
If you start the Application Server with the --verbose flag, all logging and debugging output will appear on the terminal window or command prompt and the server log. If you start the Application Server in the background, debugging information is only available in the log. You can view the server log with a text editor or with the Admin Console log viewer.
To use the log viewer:
Select the Application Server node.
Select the Logging tab.
Click the Open Log Viewer button. The log viewer will open and display the last 40 entries.
If you wish to display other entries:
Click the Modify Search button.
Specify any constraints on the entries you want to see.
Click the Search button at the bottom of the log viewer.