Is there a way to know if a Java program was started from the command line or from a jar file?

Question

I want to either display a message in the console or a pop up, so in case a parameter is not specified, I want to know to which should I display

Something like:

if( !file.exists() ) {     if( fromCommandLine()){         System.out.println("File doesn't exists");     }else if ( fromDoubleClickOnJar() ) {         JOptionPane.showMessage(null, "File doesn't exists");     }  } 

Answer 1

The straight forward answer is that you cannot tell how the JVM was launched.

But for the example use-case in your question, you don't really need to know how the JVM was launched. What you really need to know is whether the user will see a message written to the console. And the way to do that would be something like this:

if (!file.exists()) {     Console console = System.console();     if (console != null) {         console.format("File doesn't exists%n");     } else if (!GraphicsEnvironment.isHeadless()) {         JOptionPane.showMessage(null, "File doesn't exists");     } else {         // Put it in the log     }  } 

The javadoc for Console, while not water tight, strongly hints that a Console object (if it exists) writes to a console and cannot be redirected.

Thanks @Stephen Denne for the !GraphicsEnvironment.isHeadless() tip.