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[giflw]

AsciidocFX 1.5.5

Kubuntu 64bits:
Distributor ID: Ubuntu
Description: Ubuntu 16.04.2 LTS
Release: 16.04
Codename: xenial

OpenJDK 8:
openjdk version "1.8.0_121"
OpenJDK Runtime Environment (build 1.8.0_121-8u121-b13-0ubuntu1.16.04.2-b13)
OpenJDK 64-Bit Server VM (build 25.121-b13, mixed mode)

java.lang.ClassNotFoundException: com.sun.deploy.uitoolkit.impl.fx.HostServicesFactory
        at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
        at java.lang.Class.forName0(Native Method)
        at java.lang.Class.forName(Class.java:348)
        at com.sun.javafx.application.HostServicesDelegate.lambda$getInstance$0(HostServicesDelegate.java:52)
        at java.security.AccessController.doPrivileged(Native Method)
        at com.sun.javafx.application.HostServicesDelegate.getInstance(HostServicesDelegate.java:45)
        at javafx.application.HostServices.<init>(HostServices.java:52)
        at javafx.application.Application.getHostServices(Application.java:334)
        at com.kodcu.boot.AppStarter.lambda$startApp$1(AppStarter.java:110)
        at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
        at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
        at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
        at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
        at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
        at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
        at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
        at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
        at javafx.event.Event.fireEvent(Event.java:198)
        at javafx.stage.Window.fireEvent(Window.java:1120)
        at javafx.stage.Window$9.invalidated(Window.java:818)
        at javafx.beans.property.BooleanPropertyBase.markInvalid(BooleanPropertyBase.java:109)
        at javafx.beans.property.BooleanPropertyBase.set(BooleanPropertyBase.java:144)
        at javafx.stage.Window.setShowing(Window.java:922)
        at javafx.stage.Window.show(Window.java:937)
        at javafx.stage.Stage.show(Stage.java:259)
        at com.kodcu.boot.AppStarter.lambda$startApp$3(AppStarter.java:128)
        at com.kodcu.service.ThreadService.lambda$runActionLater$2(ThreadService.java:84)
        at com.sun.javafx.application.PlatformImpl.lambda$null$117(PlatformImpl.java:295)
        at java.security.AccessController.doPrivileged(Native Method)
        at com.sun.javafx.application.PlatformImpl.lambda$runLater$118(PlatformImpl.java:294)
        at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:95)
        at com.sun.glass.ui.gtk.GtkApplication._runLoop(Native Method)
        at com.sun.glass.ui.gtk.GtkApplication.lambda$null$450(GtkApplication.java:139)
        at java.lang.Thread.run(Thread.java:745)
[Fatal Error] entities.ent:16:3: The markup in the document preceding the root element must be well-formed.
[Fatal Error] l10n.xml:2:10: DOCTYPE is disallowed when the feature "http://apache.org/xml/features/disallow-doctype-decl" set to true.
[Fatal Error] l10n.dtd:1:3: The markup in the document preceding the root element must be well-formed.
[Fatal Error] targetdatabase.dtd:4:3: The markup in the document preceding the root element must be well-formed.
[Fatal Error] common.xsl:2:10: DOCTYPE is disallowed when the feature "http://apache.org/xml/features/disallow-doctype-decl" set to true.
[Fatal Error] autoidx-kosek.xsl:2:10: DOCTYPE is disallowed when the feature "http://apache.org/xml/features/disallow-doctype-decl" set to true.
[Fatal Error] autoidx-kimber.xsl:2:10: DOCTYPE is disallowed when the feature "http://apache.org/xml/features/disallow-doctype-decl" set to true.

...

411578 [JavaFX Application Thread] ERROR c.k.c.ApplicationController - null 
java.lang.NullPointerException: null
        at javafx.application.HostServices.showDocument(HostServices.java:127)
        at com.kodcu.controller.ApplicationController.browseInDesktop(ApplicationController.java:1098)
        at com.kodcu.component.HtmlPane.browse(HtmlPane.java:70)
        at java.util.Optional.ifPresent(Optional.java:159)
        at com.kodcu.controller.ApplicationController.externalBrowse(ApplicationController.java:1872)
        at com.kodcu.controller.ApplicationController.lambda$initializeApp$45(ApplicationController.java:820)
        at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
        at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
        at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
        at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
        at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
        at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
        at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
        at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
        at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
        at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
        at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
        at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
        at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
        at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
        at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
        at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
        at javafx.event.Event.fireEvent(Event.java:198)
        at javafx.scene.Scene$ClickGenerator.postProcess(Scene.java:3470)
        at javafx.scene.Scene$ClickGenerator.access$8100(Scene.java:3398)
        at javafx.scene.Scene$MouseHandler.process(Scene.java:3766)
        at javafx.scene.Scene$MouseHandler.access$1500(Scene.java:3485)
        at javafx.scene.Scene.impl_processMouseEvent(Scene.java:1762)
        at javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2494)
        at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:352)
        at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:275)
        at java.security.AccessController.doPrivileged(Native Method)
        at com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$300(GlassViewEventHandler.java:388)
        at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:389)
        at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:387)
        at com.sun.glass.ui.View.handleMouseEvent(View.java:555)
        at com.sun.glass.ui.View.notifyMouse(View.java:937)
        at com.sun.glass.ui.gtk.GtkApplication._runLoop(Native Method)
        at com.sun.glass.ui.gtk.GtkApplication.lambda$null$450(GtkApplication.java:139)
        at java.lang.Thread.run(Thread.java:745)

[rahmanusta]

It looks something wrong with your openjdk build. You can use oracle jdk included in releases.