Java.awt.headlessexception is an exception that occurs when a program is not able to run in an environment with no graphical display. This often occurs when a program has been developed for a GUI-based system, and then attempts to run within an environment that does not provide the necessary graphical support. The exception can occur when running a program from a terminal, or when attempting to run a program in a web server without the proper support.
Symptoms
When this exception occurs, the program will display an error message akin to "Exception in thread 'main' java.awt.headlessexception: no X11 DISPLAY variable was set," indicating that the program was unable to run in the current environment. This exception can also manifest itself in other forms, depending on what code was being run. It is commonly seen when attempting to run GUI-based programs in a terminal or SSH session.
Causes
This exception occurs when a program that is designed for a Graphical User Interface (or GUI) attempted to run in an environment without the necessary graphical components required to display the user interface. This often occurs when a program is tested by a user or in process, and the necessary components are not taken into account. The exception can also occur when attempting to run a GUI-based program in a web server environment, such as Tomcat.
Solutions
For users who are attempting to run a GUI-based program from their terminal, the simplest solution is to run the program from the system that it was intended to run on. However, if this is not possible, there are other steps you can take to resolve this problem.
Install the Necessary GUI Driver: Depending on your operating system, you may have to install the graphical drivers that are necessary to support the program. This can be done by installing any necessary packages that might be given with the program, or running commands such as "sudo apt install xserver-xorg-video-all" in a terminal environment to ensure that your system has the drivers necessary to support it.
Make Sure the System Includes Necessary X11/Other Libraries: Additionally, if the program needs to link to X11 or other programs in order to run, you should make sure that these are installed and available. You can install packages for them, or make sure the programs can reference them by altering environment variables.
FAQ
Q: What is the cause of Java.awt.headlessexception?
A: This exception occurs when a program that is designed for a Graphical User Interface (or GUI) attempted to run in an environment without the necessary graphical components required to display the user interface. This can occur when running a program in a terminal, or when attempting to run a program in a web server without the proper support.
Q: How do I fix this exception?
A: The simplest solution is to run the program from the system that it was intended to run on. However, if this is not possible, you can install the necessary graphical drivers, make sure that your system includes necessary X11/other libraries, and alter environment variables if necessary.
Q: What other exceptions may manifest themselves in a similar way?
A: This exception can manifest itself in other forms, depending on what code was being run. Other exceptions related to headless environments include NoClassDefFoundError, NoSuchMethodError, NoSuchFieldError, java.io.IOException, and ClassNotFoundException.