Check the application server standard output and standard error log files for errors. For information on the application server log files and where they are located, see WebSphere Application Server - Express log files.
Add logging and tracing to your application with the JRas framework. See Use the application server trace service for more information.
Add output to your Java code in the form of System.out.println() statements to aid in debugging. The output from any System.out.println() statements is written to the standard output log file for the application server in which the code is running. For information on the application server log files and where they are located, see WebSphere Application Server - Express log files.
Read the release notes. See WebSphere Application Server - Express Release Notes 
for
more information.