Configure Built-In plantuml to not steal keyboard focus on MacOS X

[arthurvl]

Is your feature request related to a problem? Please describe.
Running a JavaDoc with UMLDoclet from maven repeatedly steals keyboard focus on MacOS X. This makes it hard to use the computer while the javadoc generation is running.

Describe the solution you'd like
It would be good to provide a mechanism to set the java.awt.headless=true property for the run context of the built-in plantuml, or do so by default.

Describe alternatives you've considered
Setting java.awt.headless through _JAVA_OPTIONS works but is somewhat clunky. Neither JAVA_OPTS nor MAVEN_OPTS will be picked up. Setting it through additionalJOptions or additionalOptions also does not work. Having to set it at all can now only be documented in a readme or faq, rather than set in e.g. the pom.xml.

[sjoerdtalsma]

Thank you for the investigation.
I looked into this and there seems to be something already setting the 'headless' state before the doclet class even gets loaded:

public class UMLDoclet extends StandardDoclet {
    static {
        System.setProperty("java.awt.headless", "true");
    }
    // ...
    public UMLDoclet() {
        super();
        this.config = new DocletConfig();
        System.out.println("Headless? java.awt.headless=" + System.getProperty("java.awt.headless")
                + ", GraphicsEnvironment.isHeadless()=" + java.awt.GraphicsEnvironment.isHeadless());
    }
}

Results in: Headless? java.awt.headless=true, GraphicsEnvironment.isHeadless()=false

The java module system also prevents us from using filthy reflection tools to try manipulate the private static GraphicsEnvironment.headless field directly.

Do you have other suggestions that will autoconfigure the built-in PlantUML behave decently?

[sjoerdtalsma]

Perhaps the maven javadoc plugin could (/should) set this system property by default?
I can't imagine any usecase for running anything non-headless from the javadoc plugin.

[sjoerdtalsma]

Results in: Headless? java.awt.headless=true, GraphicsEnvironment.isHeadless()=false

Okay, that may have been a bit premature running tests from my IDE 🫣.

Commandline maven gives me:

[INFO] --- maven-javadoc-plugin:3.6.3:jar (attach-javadocs) @ umldoclet ---
[INFO] No previous run data found, generating javadoc.
[INFO] 
Headless? java.awt.headless=true, GraphicsEnvironment.isHeadless()=true

I'll create a version where I set the java.awt.headless system property directly when loading the doclet class (first 'contact' UMLDoclet gets). It won't hurt and might even fix the issue. 🤞

[sjoerdtalsma]

@arthurvl Could you please check whether the problem still exists with version 2.1.2?

[sjoerdtalsma]

Closing this issue to lack of activity. @arthurvl feel free to re-open if you still experience this issue with the latest version.