Font error

[tobiasBora]

Thanks for this super cool software. I just gave it a try, and when it starts it prints an error message Unable to load system fonts, no directory is readable:

And the console shows:

$ ./PDF4Teachers
WARNING: Unknown module: PDF4Teachers.master.merged.module specified to --add-reads
WARNING: Unknown module: PDF4Teachers.master.merged.module specified to --add-exports
01:58:15.424 INFO    Main main() Starting PDF4Teachers 1.4.4 | Java 21.0.4 on JFX 22+30 (amd64) on Linux 6.12.32
01:58:15.427 INFO    Main main() Run mode: release | Log level: info

(PDF4Teachers:166841): Gdk-WARNING **: 13:58:16.033: XSetErrorHandler() called with a GDK error trap pushed. Don't do that.
01:58:16.510 INFO    SystemFontsMapper loadFontsFromSystemFiles() Indexing system fonts... (325 fonts)
01:58:16.515 CONSOLE [ERROR] Exception in thread "System fonts loader" 01:58:16.517 CONSOLE [ERROR] java.lang.IllegalStateException: Not on FX application thread; currentThread = System fonts loader
01:58:16.517 CONSOLE [ERROR]    at javafx.graphics@22/com.sun.javafx.tk.Toolkit.checkFxUserThread(Unknown Source)
01:58:16.517 CONSOLE [ERROR]    at javafx.graphics@22/com.sun.javafx.tk.quantum.QuantumToolkit.checkFxUserThread(Unknown Source)
01:58:16.517 CONSOLE [ERROR]    at javafx.graphics@22/javafx.scene.Parent$3.onProposedChange(Unknown Source)
01:58:16.518 CONSOLE [ERROR]    at javafx.base@22/com.sun.javafx.collections.VetoableListDecorator.setAll(Unknown Source)
01:58:16.518 CONSOLE [ERROR]    at javafx.base@22/com.sun.javafx.collections.VetoableListDecorator.setAll(Unknown Source)
01:58:16.518 CONSOLE [ERROR]    at javafx.controls@22/javafx.scene.control.skin.LabeledSkinBase.updateChildren(Unknown Source)
01:58:16.518 CONSOLE [ERROR]    at javafx.controls@22/javafx.scene.control.skin.LabeledSkinBase.lambda$new$11(Unknown Source)
01:58:16.518 CONSOLE [ERROR]    at javafx.controls@22/com.sun.javafx.scene.control.LambdaMultiplePropertyChangeListenerHandler.lambda$new$1(Unknown Source)
01:58:16.518 CONSOLE [ERROR]    at javafx.base@22/javafx.beans.value.WeakChangeListener.changed(Unknown Source)
01:58:16.518 CONSOLE [ERROR]    at javafx.base@22/com.sun.javafx.binding.ExpressionHelper$SingleChange.fireValueChangedEvent(Unknown Source)
01:58:16.518 CONSOLE [ERROR]    at javafx.base@22/com.sun.javafx.binding.ExpressionHelper.fireValueChangedEvent(Unknown Source)
01:58:16.519 CONSOLE [ERROR]    at javafx.base@22/javafx.beans.property.StringPropertyBase.fireValueChangedEvent(Unknown Source)
01:58:16.519 CONSOLE [ERROR]    at javafx.base@22/javafx.beans.property.StringPropertyBase.markInvalid(Unknown Source)
01:58:16.519 CONSOLE [ERROR]    at javafx.base@22/javafx.beans.property.StringPropertyBase.set(Unknown Source)
01:58:16.519 CONSOLE [ERROR]    at javafx.base@22/javafx.beans.property.StringPropertyBase.set(Unknown Source)
01:58:16.519 CONSOLE [ERROR]    at javafx.base@22/javafx.beans.property.StringProperty.setValue(Unknown Source)
01:58:16.520 CONSOLE [ERROR]    at javafx.controls@22/javafx.scene.control.Labeled.setText(Unknown Source)
01:58:16.520 CONSOLE [ERROR]    at org.controlsfx.controls@11.2.1/impl.org.controlsfx.skin.NotificationPaneSkin.lambda$new$2(Unknown Source)
01:58:16.520 CONSOLE [ERROR]    at javafx.controls@22/com.sun.javafx.scene.control.LambdaMultiplePropertyChangeListenerHandler.lambda$new$1(Unknown Source)
01:58:16.520 CONSOLE [ERROR]    at javafx.base@22/javafx.beans.value.WeakChangeListener.changed(Unknown Source)
01:58:16.520 CONSOLE [ERROR]    at javafx.base@22/com.sun.javafx.binding.ExpressionHelper$SingleChange.fireValueChangedEvent(Unknown Source)
01:58:16.520 CONSOLE [ERROR]    at javafx.base@22/com.sun.javafx.binding.ExpressionHelper.fireValueChangedEvent(Unknown Source)
01:58:16.520 CONSOLE [ERROR]    at javafx.base@22/javafx.beans.property.StringPropertyBase.fireValueChangedEvent(Unknown Source)
01:58:16.521 CONSOLE [ERROR]    at javafx.base@22/javafx.beans.property.StringPropertyBase.markInvalid(Unknown Source)
01:58:16.521 CONSOLE [ERROR]    at javafx.base@22/javafx.beans.property.StringPropertyBase.set(Unknown Source)
01:58:16.521 CONSOLE [ERROR]    at javafx.base@22/javafx.beans.property.StringPropertyBase.set(Unknown Source)
01:58:16.521 CONSOLE [ERROR]    at org.controlsfx.controls@11.2.1/org.controlsfx.control.NotificationPane.setText(Unknown Source)
01:58:16.521 CONSOLE [ERROR]    at org.controlsfx.controls@11.2.1/org.controlsfx.control.NotificationPane$7.run(Unknown Source)
01:58:16.521 CONSOLE [ERROR]    at org.controlsfx.controls@11.2.1/org.controlsfx.control.NotificationPane.hideAndThen(Unknown Source)
01:58:16.522 CONSOLE [ERROR]    at org.controlsfx.controls@11.2.1/org.controlsfx.control.NotificationPane.show(Unknown Source)
01:58:16.522 CONSOLE [ERROR]    at fr.clementgre.pdf4teachers/fr.clementgre.pdf4teachers.interfaces.AutoHideNotificationPane.lambda$show$2(Unknown Source)
01:58:16.522 CONSOLE [ERROR]    at fr.clementgre.pdf4teachers/fr.clementgre.pdf4teachers.interfaces.AutoHideNotificationPane.hideAndThen(Unknown Source)
01:58:16.522 CONSOLE [ERROR]    at fr.clementgre.pdf4teachers/fr.clementgre.pdf4teachers.interfaces.AutoHideNotificationPane.show(Unknown Source)
01:58:16.522 CONSOLE [ERROR]    at fr.clementgre.pdf4teachers/fr.clementgre.pdf4teachers.interfaces.AutoHideNotificationPane.show(Unknown Source)
01:58:16.522 CONSOLE [ERROR]    at fr.clementgre.pdf4teachers/fr.clementgre.pdf4teachers.interfaces.AutoHideNotificationPane.checkPending(Unknown Source)
01:58:16.522 CONSOLE [ERROR]    at fr.clementgre.pdf4teachers/fr.clementgre.pdf4teachers.interfaces.AutoHideNotificationPane.addToPending(Unknown Source)
01:58:16.522 CONSOLE [ERROR]    at fr.clementgre.pdf4teachers/fr.clementgre.pdf4teachers.interfaces.windows.MainWindow.showNotification(Unknown Source)
01:58:16.522 CONSOLE [ERROR]    at fr.clementgre.pdf4teachers/fr.clementgre.pdf4teachers.utils.fonts.SystemFontsMapper.getSystemFontsDirs(Unknown Source)
01:58:16.522 CONSOLE [ERROR]    at fr.clementgre.pdf4teachers/fr.clementgre.pdf4teachers.utils.fonts.SystemFontsMapper.getAllSystemFontFiles(Unknown Source)
01:58:16.523 CONSOLE [ERROR]    at fr.clementgre.pdf4teachers/fr.clementgre.pdf4teachers.utils.fonts.SystemFontsMapper.lambda$loadFontsFromSystemFiles$3(Unknown Source)
01:58:16.523 CONSOLE [ERROR]    at java.base/java.lang.Thread.run(Unknown Source)
01:58:16.523 CONSOLE [ERROR] Exception in thread "System fonts loader" 01:58:16.523 CONSOLE [ERROR] java.lang.IllegalStateException: Not on FX application thread; currentThread = System fonts loader
01:58:16.523 CONSOLE [ERROR]    at javafx.graphics@22/com.sun.javafx.tk.Toolkit.checkFxUserThread(Unknown Source)
01:58:16.523 CONSOLE [ERROR]    at javafx.graphics@22/com.sun.javafx.tk.quantum.QuantumToolkit.checkFxUserThread(Unknown Source)
01:58:16.524 CONSOLE [ERROR]    at javafx.graphics@22/javafx.scene.Parent$3.onProposedChange(Unknown Source)
01:58:16.524 CONSOLE [ERROR]    at javafx.base@22/com.sun.javafx.collections.VetoableListDecorator.setAll(Unknown Source)
01:58:16.524 CONSOLE [ERROR]    at javafx.base@22/com.sun.javafx.collections.VetoableListDecorator.setAll(Unknown Source)
01:58:16.524 CONSOLE [ERROR]    at javafx.controls@22/javafx.scene.control.skin.LabeledSkinBase.updateChildren(Unknown Source)
01:58:16.524 CONSOLE [ERROR]    at javafx.controls@22/javafx.scene.control.skin.LabeledSkinBase.lambda$new$5(Unknown Source)
01:58:16.524 CONSOLE [ERROR]    at javafx.controls@22/com.sun.javafx.scene.control.LambdaMultiplePropertyChangeListenerHandler.lambda$new$1(Unknown Source)
01:58:16.524 CONSOLE [ERROR]    at javafx.base@22/javafx.beans.value.WeakChangeListener.changed(Unknown Source)
01:58:16.524 CONSOLE [ERROR]    at javafx.base@22/com.sun.javafx.binding.ExpressionHelper$SingleChange.fireValueChangedEvent(Unknown Source)
01:58:16.524 CONSOLE [ERROR]    at javafx.base@22/com.sun.javafx.binding.ExpressionHelper.fireValueChangedEvent(Unknown Source)
01:58:16.524 CONSOLE [ERROR]    at javafx.base@22/javafx.beans.property.ObjectPropertyBase.fireValueChangedEvent(Unknown Source)
01:58:16.525 CONSOLE [ERROR]    at javafx.base@22/javafx.beans.property.ObjectPropertyBase.markInvalid(Unknown Source)
01:58:16.525 CONSOLE [ERROR]    at javafx.base@22/javafx.beans.property.ObjectPropertyBase.set(Unknown Source)
01:58:16.525 CONSOLE [ERROR]    at javafx.graphics@22/javafx.css.StyleableObjectProperty.set(Unknown Source)
01:58:16.525 CONSOLE [ERROR]    at javafx.base@22/javafx.beans.property.ObjectProperty.setValue(Unknown Source)
01:58:16.525 CONSOLE [ERROR]    at javafx.controls@22/javafx.scene.control.Labeled.setGraphic(Unknown Source)
01:58:16.525 CONSOLE [ERROR]    at org.controlsfx.controls@11.2.1/impl.org.controlsfx.skin.NotificationPaneSkin.lambda$new$3(Unknown Source)
01:58:16.525 CONSOLE [ERROR]    at javafx.controls@22/com.sun.javafx.scene.control.LambdaMultiplePropertyChangeListenerHandler.lambda$new$1(Unknown Source)
01:58:16.525 CONSOLE [ERROR]    at javafx.base@22/javafx.beans.value.WeakChangeListener.changed(Unknown Source)
01:58:16.526 CONSOLE [ERROR]    at javafx.base@22/com.sun.javafx.binding.ExpressionHelper$SingleChange.fireValueChangedEvent(Unknown Source)
01:58:16.526 CONSOLE [ERROR]    at javafx.base@22/com.sun.javafx.binding.ExpressionHelper.fireValueChangedEvent(Unknown Source)
01:58:16.526 CONSOLE [ERROR]    at javafx.base@22/javafx.beans.property.ObjectPropertyBase.fireValueChangedEvent(Unknown Source)
01:58:16.526 CONSOLE [ERROR]    at javafx.base@22/javafx.beans.property.ObjectPropertyBase.markInvalid(Unknown Source)
01:58:16.526 CONSOLE [ERROR]    at javafx.base@22/javafx.beans.property.ObjectPropertyBase.set(Unknown Source)
01:58:16.526 CONSOLE [ERROR]    at org.controlsfx.controls@11.2.1/org.controlsfx.control.NotificationPane.setGraphic(Unknown Source)
01:58:16.526 CONSOLE [ERROR]    at org.controlsfx.controls@11.2.1/org.controlsfx.control.NotificationPane$7.run(Unknown Source)
01:58:16.526 CONSOLE [ERROR]    at org.controlsfx.controls@11.2.1/org.controlsfx.control.NotificationPane.hideAndThen(Unknown Source)
01:58:16.526 CONSOLE [ERROR]    at org.controlsfx.controls@11.2.1/org.controlsfx.control.NotificationPane.show(Unknown Source)
01:58:16.526 CONSOLE [ERROR]    at fr.clementgre.pdf4teachers/fr.clementgre.pdf4teachers.interfaces.AutoHideNotificationPane.lambda$show$2(Unknown Source)
01:58:16.527 CONSOLE [ERROR]    at fr.clementgre.pdf4teachers/fr.clementgre.pdf4teachers.interfaces.AutoHideNotificationPane.hideAndThen(Unknown Source)
01:58:16.527 CONSOLE [ERROR]    at fr.clementgre.pdf4teachers/fr.clementgre.pdf4teachers.interfaces.AutoHideNotificationPane.show(Unknown Source)
01:58:16.527 CONSOLE [ERROR]    at fr.clementgre.pdf4teachers/fr.clementgre.pdf4teachers.interfaces.AutoHideNotificationPane.show(Unknown Source)
01:58:16.527 CONSOLE [ERROR]    at fr.clementgre.pdf4teachers/fr.clementgre.pdf4teachers.interfaces.AutoHideNotificationPane.checkPending(Unknown Source)
01:58:16.527 CONSOLE [ERROR]    at fr.clementgre.pdf4teachers/fr.clementgre.pdf4teachers.interfaces.AutoHideNotificationPane.addToPending(Unknown Source)
01:58:16.527 CONSOLE [ERROR]    at fr.clementgre.pdf4teachers/fr.clementgre.pdf4teachers.interfaces.windows.MainWindow.showNotification(Unknown Source)
01:58:16.527 CONSOLE [ERROR]    at fr.clementgre.pdf4teachers/fr.clementgre.pdf4teachers.utils.fonts.SystemFontsMapper.getSystemFontsDirs(Unknown Source)
01:58:16.528 CONSOLE [ERROR]    at fr.clementgre.pdf4teachers/fr.clementgre.pdf4teachers.utils.fonts.SystemFontsMapper.getAllSystemFontFiles(Unknown Source)
01:58:16.528 CONSOLE [ERROR]    at fr.clementgre.pdf4teachers/fr.clementgre.pdf4teachers.utils.fonts.SystemFontsMapper.lambda$loadFontsFromSystemFiles$3(Unknown Source)
01:58:16.528 CONSOLE [ERROR]    at java.base/java.lang.Thread.run(Unknown Source)
01:58:16.534 INFO    SystemFontsMapper lambda$loadFontsFromSystemFiles$3() Loaded 0/325 fonts in 0.02s (0 unable to load due to PDFBox restrictions, usually missing tables)

I don't know if it matters, but I use NixOS (via nix-ld), that may uses non-standard directory (notably it does not use /usr etc), but does follow XDG specifications to provide environment variables poiting to appropriate folders etc.

[ClementGre]

An error did occured loading the fonts, but generated a notification that threw an error when trying to display due to a bug.

The error is

Error: unable to load system fonts, no directory is readable

Meaning that no font was loaded. Here are the directories in which PDF4Teachers tries to find font files:

• ~/.fonts
• /usr/share/fonts/truetype
• /usr/share/fonts/TTF
• /usr/local/share/fonts/

The error occurs because PDF4Teachers can’t read/write files in these directories, but there might be a bug there.

To fix the notification bug:
That line should run on the UI thread:
https://github.com/ClementGre/PDF4Teachers/blob/b016f062c3b067b88b4d0e38d0b5f382104cef75/src/main/java/fr/clementgre/pdf4teachers/utils/fonts/SystemFontsMapper.java#L83C1-L83C136

[tobiasBora]

Thanks for your answer. This explains the issue then: NixOS does not use stuff in /usr (the system share folder would rather be /run/current-system/sw/share but it uses many more folders as well for locally installed packages etc). So instead it specifies as recommended by XDG's specification all "share" folders in the environment variable XDG_DATA_DIRS:

$ echo $XDG_DATA_DIRS
/nix/store/kxkmnhgd06qp5yrxh0a64p8vpad9iqwb-konsole-25.08.3/share:/nix/store/s9gpyskqq47vcvphm0h10144blwkq8kn-kpty-6.20.0/share:[…]:/nix/store/yp9c76fj59a9lcn4afp4rylrhjzqk129-cups-2.4.14-lib/share:/nix/store/5l5wsn4qxkw90h6sxxz43gbnar7w5x8s-fontconfig-2.17.1-lib/share:/nix/store/mr5l9d6bvv80n2s8l8dyms4l90gpjkkd-util-linux-2.41.2-lib/share:/nix/store/zf8qy81dsw1vqwgh9p9n2h40s1k0g2l1-systemd-258.2/share:/nix/store/5qdsnc26nv61j5rrw492f19xav2rz45v-glib-2.86.1/share:/nix/store/kwr2jkqrbf6gsalagrka7gb7yrn71qpi-gettext-0.25.1/share:/nix/store/00bxhcd7dwmj3b3kabd90y9dbdxvqi8l-desktops/share:/home/leo/.local/share/flatpak/exports/share:/var/lib/flatpak/exports/share:/home/leo/.nix-profile/share:/nix/profile/share:/home/leo/.local/state/nix/profile/share:/etc/profiles/per-user/leo/share:/nix/var/nix/profiles/default/share:/run/current-system/sw/share

You can notably see /run/current-system/sw/share inside but it is not the only one, and actually I don't have fonts in /run/current-system/sw/share/fonts. I do have many fonts in /home/leo/.nix-profile/share/fonts, and some in /run/current-system/sw/share/X11/fonts/… But I think the "clean" way to proceed is to rely on fc-list (or I guess libraries based on fontconfig), that will also cache the list of fonts, get them from other config files etc:

$ fc-list
/nix/store/kxvpxm5ygx9a3mvi75qbm5gq43fsbb4m-noto-fonts-2025.11.01/share/fonts/noto/NotoSerifMyanmar[wdth,wght].ttf: Noto Serif Myanmar:style=Black
/home/leo/.nix-profile/share/fonts/truetype/Tinos Bold for Powerline.ttf: Tinos for Powerline:style=Bold
/nix/store/vhsvr7bq2fa0nlb08xhrw5g8ysvryvip-corefonts-1/share/fonts/truetype/Courier_New.ttf: Courier New:style=Regular,Normal,obyčejné,Standard,Κανονικά,Normaali,Normál,Normale,Standaard,Normalny,Обычный,Normálne,Navadno,thường,Arrunta
/nix/store/kxvpxm5ygx9a3mvi75qbm5gq43fsbb4m-noto-fonts-2025.11.01/share/fonts/noto/NotoSansCherokee[wght].ttf: Noto Sans Cherokee:style=Bold
/nix/store/kxvpxm5ygx9a3mvi75qbm5gq43fsbb4m-noto-fonts-2025.11.01/share/fonts/noto/NotoSansCham[wght].ttf: Noto Sans Cham:style=Medium
/nix/store/kxvpxm5ygx9a3mvi75qbm5gq43fsbb4m-noto-fonts-2025.11.01/share/fonts/noto/NotoSansSymbols[wght].ttf: Noto Sans Symbols:style=ExtraLight
/nix/store/kxvpxm5ygx9a3mvi75qbm5gq43fsbb4m-noto-fonts-2025.11.01/share/fonts/noto/NotoSerifTamil[wdth,wght].ttf: Noto Serif Tamil
/nix/store/kxvpxm5ygx9a3mvi75qbm5gq43fsbb4m-noto-fonts-2025.11.01/share/fonts/noto/NotoSerifThai[wdth,wght].ttf: Noto Serif Thai:style=ExtraBold
/nix/store/kxvpxm5ygx9a3mvi75qbm5gq43fsbb4m-noto-fonts-2025.11.01/share/fonts/noto/NotoSansDevanagari[wdth,wght].ttf: Noto Sans Devanagari
/nix/store/kxvpxm5ygx9a3mvi75qbm5gq43fsbb4m-noto-fonts-2025.11.01/share/fonts/noto/NotoSansMahajani-Regular.otf: Noto Sans Mahajani:style=Regular
/nix/store/kxvpxm5ygx9a3mvi75qbm5gq43fsbb4m-noto-fonts-2025.11.01/share/fonts/noto/NotoSansGunjalaGondi[wght].ttf: Noto Sans Gunjala Gondi
/nix/store/kxvpxm5ygx9a3mvi75qbm5gq43fsbb4m-noto-fonts-2025.11.01/share/fonts/noto/NotoSansNandinagari-Regular.otf: Noto Sans Nandinagari:style=Regular
/nix/store/kxvpxm5ygx9a3mvi75qbm5gq43fsbb4m-noto-fonts-2025.11.01/share/fonts/noto/NotoSansMalayalam[wdth,wght].ttf: Noto Sans Malayalam:style=ExtraLight
/nix/store/vmrvlfg3j46942d7wjp3qa93yvmrslif-gyre-fonts-2.005/share/fonts/truetype/texgyrepagella-bolditalic.otf: TeX Gyre Pagella:style=Bold Italic
/nix/store/kxvpxm5ygx9a3mvi75qbm5gq43fsbb4m-noto-fonts-2025.11.01/share/fonts/noto/NotoSansGurmukhi[wdth,wght].ttf: Noto Sans Gurmukhi:style=SemiBold
/nix/store/vhsvr7bq2fa0nlb08xhrw5g8ysvryvip-corefonts-1/share/fonts/truetype/Comic_Sans_MS.ttf: Comic Sans MS:style=Regular,Normal,obyčejné,Standard,Κανονικά,Normaali,Normál,Normale,Standaard,Normalny,Обычный,Normálne,Navadno,Arrunta
…

also, note that ~/.fonts is deprecated. It should be $XDG_DATA_HOME/fonts that defaults to ~/.local/share/fonts/.

[tobiasBora]

Also, note that in java, you may want to use https://docs.oracle.com/javase/8/docs/api/java/awt/GraphicsEnvironment.html notably getAllFonts?

[ClementGre]

Thank you for the details, I should be able to provide a fix for this in the next release.

PDF4Teachers needs to not only get the font names, but also their location on the disk for the export of the text in PDFs.
Then, PDF4Teachers do use GraphicsEnvironment.getLocalGraphicsEnvironment().getAvailableFontFamilyNames() (it detected 325 fonts on your computer), but I couldn’t find how to find the source file using GraphicsEnvironment or the java.awt.Font class, so I manually look for the files on the computer, which is a bit of a tricky thing.

[tobiasBora]

I see thanks. Then maybe simply parsing

$ fc-list --format=%{file}:::%{family}
/nix/store/10vg33f60ypafd0qvn1ym56m2219jqiw-dejavu-fonts-minimal-2.37/share/fonts/truetype/DejaVuSans.ttf:::DejaVu Sans

is the simplest solution