Debugging Applications

When you enable debugging, you enable both local and remote debugging. To start the server in debug mode, use the --debug option as follows:

You can then attach to the server from the Java Debugger (jdb) at its default Java Platform Debugger Architecture (JPDA) port, which is 9009.

For example, in UNIX systems:

And for Windows OS:

For more information about the jdb debugger, see the following official Java SE 11 documentation links:

Payara Server debugging is based on JPDA. For more information, see JPDA Options.

You can attach any JPDA compliant debugger to Payara Server, including that of all major Java IDE environments like IntelliJ, Apache Netbeans, Eclipse and Visual Studio Code.

You can enable debugging even when Payara Server is started without the --debug option. This is useful in development environments where you want to make sure that debugging is always turned on.

The default JPDA options in Payara Server are as follows:

If you specify suspend=y, the JVM software 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 process starts.

To specify a different port (from 9009, the default) to use when attaching the JVM software to a debugger, specify address=<port-number>.

You can include any additional options if needed.

To generate a Java stack trace for debugging purposes, use the asadmin generate-jvm-report --type=thread command. The generated stack trace goes to the domain-dir/logs/server.log file and also appears on the command prompt screen.

For more information about the asadmin generate-jvm-report command, see generate-jvm-report.

When the appclient script executes the java command to run the Application Client Container (ACC), which in turn runs the client itself, it includes on the command line the value of the VMARGS environment variable. You can set this variable to any suitable value. For example:

You should use different ports for the server and client if you are debugging both concurrently. For details about setting the port, see JPDA Options.

You can also include JVM options in the appclient script directly. For information about the appclient script, see appclient.

Open Message Queue has a broker logger, which can be useful for debugging Java Message Service (JMS) applications, including message-driven bean applications.

You can adjust the logger’s verbosity, and you can send the logger output to the broker’s console using the broker’s -tty option.

To have the server logs and messages printed to System.out on your command prompt screen, you can start the server in verbose mode. This makes it easy to do simple debugging using print statements, without having to check the server.log file every time.

To start the domain in verbose mode, use the --verbose option as follows:

When the server is in verbose mode, messages are logged to the console or terminal window in addition to the log file. In addition, pressing Ctrl-C stops the server and pressing Ctrl-\ (on UNIX platforms) or Ctrl-Break (on Windows OS) prints a thread dump.

On UNIX platforms, you can also print a thread dump using the jstack command or the command kill -QUIT <process_id>.

To generate class loading messages you can use the -Xlog JVM argument by running the following asadmin create-jvm-options command:

As classloading debugging messages will heavily populate the standard output, it is recommended to log these entries on a special log file. The -Xlog argument can be appended with the

To send the JVM messages to a special JVM log file instead of stdout, use the following asadmin create-jvm-options command instead:

It is recommended that this log is located in the standard logs directory output like so: