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Troubleshooting JVM apps

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Problems loading native libraries

Conveyor can move native libraries out of JARS to ensure a better end-user experience. It's conventional to always try to load native libraries using System.loadLibrary before unpacking bundled native code, but some libraries don't do this.

You have two possible solutions:

  • Set app.jvm.extract-native-libraries = false. This will cause Conveyor to find and sign any native libraries inside the JARs, allowing your app to extract them to the user's home directory or temp directory at startup. It's not ideal because it will litter your user's system with stuff that uninstalls won't clean up, it slows down app startup, bloats your download and can cause problems with Apple's GateKeeper (see below). But it is simple for the developer and will get you running fast.
  • Provide the right system properties for your third party library to find its native code. You can do it using the special <libpath> token, like this:
app {
    jvm {
        system-properties {
            "my.library.nativePathLib" = <libpath>

It's often worth reporting these bugs to the upstream projects, so they can use loadLibrary first and only try unpacking libraries afterwards.

To make library extraction easier to use we maintain an open source config that sets the right system properties for common libraries. It can be used like this:

include required("")

View source

If you find a library that needs a custom system property to be compatible with library extraction please send us a pull request.

"UnsatisfiedLinkError: ... Mapping process and mapped file (non-platform) have different Team IDs ..."

The file identified as being unloadable is probably in a cache or temp location in your home directory.

This error from macOS can occur when using an app on the same machine used to develop it. It's related to the discussion above about native libraries. When app.jvm.extract-native-libraries = false (which is the default when conveyor.compatibility-level >= 7) Java libraries with native components will go back to the regular behavior of extracting their libs at startup to somewhere in the user's home directory (or a temporary directory). During development the library that gets extracted to this cache path will be unsigned, but when you build your app the embedded .jnilib or .dylib file inside the JAR will be code signed with your identity and the operating system expects them to match. If they don't then you'll get this error. This problem is inherent to the way the JVM ecosystem handles native code and Conveyor gives you several options to resolve it.

The best solution is to opt in to native library extraction. This will place native code in the right places inside the Mac app ensuring no conflicts, fast startup time and avoiding problems with GateKeeper. The downside is you may need to set extra system properties to make your Java libraries look in the right place for their native components.

The quickest solution is to delete the file that the error identifies as being unloadable, then run your packaged and signed app. This will replace the cached version with the version from your app, signed by you. This should also work fine whilst developing your app. The problem with this is that if any of your users have two different apps that use the same Java library, then they will fight over the shared cache location and the signature mismatch error may return.

The final solution is to opt out of Apple's library validation feature. This will make the error go away in all cases without needing extra system properties. However, Apple views apps that do this to be less secure than normal and GateKeeper will run extra checks on them, which might cause your app to be blocked. Do it like this:

app {
    mac { 
        entitlements-plist {
            "" = true

Localization doesn't work when packaged

Conveyor uses jlink to shrink the size of the bundled JVM. Translations can be large, so by default jlink throws out non-US locales. To add e.g. German locale data, use config like this:

app {
    jvm {
        modules += jdk.localedata
        jlink-flags += "--include-locales=en,de"

To learn how to specify languages, please read the jlink user guide.


This popular library needs a special fix when deploying with app.jvm.extract-native-libraries = true. It uses a way to load native code that isn't quite normal nor compatible with the Java API specification. To fix it include the following class and call the fix method before accessing usb4java for the first time:

public class Usb4JavaPackaging {
    public static void fix() {
        if (System.getProperty("app.dir") == null)
            return;   // In dev, nothing to do.

        try {
            var field = org.usb4java.Loader.class.getDeclaredField("loaded");
            field.set(null, true);

            try {
            } catch (UnsatisfiedLinkError e) {

            // On Windows usb4java uses an non-Java-spec compliant DLL 
            // name, so we have to try again.
        } catch (IllegalAccessException | NoSuchFieldException e) {
            throw new RuntimeException(e);

If you don't use machine specific dependencies

If you add usb4java to your build system in the standard way, you'll end up with every possible native library JAR on your classpath. This is OK! But be aware that:

  • Your app will contain every native library JAR on every platform. If you look inside you'll notice they're empty. Conveyor extracted the native library, noticed it was for a different OS and didn't include it in the package. So don't worry, you aren't bloating your app. These empty JARs are harmless and can be ignored.
  • You will get warnings of the form libusb4java-1.3.0-linux-x86-64.jar doesn't seem to contain artifacts for mac.amd64. This is Conveyor telling you that you seem to have native libraries for the wrong OS on your classpath for each machine. Again, this is harmless in this context and can be ignored, because Conveyor will fix things automatically.

Big delta updates

You can make updates faster by using individual JARs as inputs. This will work much better with delta compression (as used by MSIX/AppInstaller on Windows). Note that explicit JPMS modules will be still be bundled into a single modules file, as this can yield better startup times.

JavaFX fails to launch on Windows citing missing dependencies in glass.dll

Upgrade to JavaFX 19 or higher. Earlier versions of JavaFX rely on the Microsoft VC++ runtime DLLs either coming with the JVM or being already installed on the user's system. Depending on what version of Visual Studio was used to compile your JDK distribute, on a clean Windows install the right DLLs may not be available. In JavaFX 19 the right DLLs are bundled in the jmods. See JDK-8281089. Conveyor will warn you if you're using JavaFX older than 19.

Error opening sockets on Windows

If you encounter an exception on Windows that ends with these frames:

Caused by: Invalid argument: connect
    at java.base/ Method)
    at java.base/
    at java.base/
    at java.base/
    at java.base/
    at java.base/$Initializer$
    at java.base/$

... then you're hitting a bug in Windows. Conveyor 8 automatically works around it, so try upgrading to that version or higher.

Native crash when using JNA on macOS

If your app uses JNA and crashes in native code with a stack trace ending in this:

Thread 0 Crashed::  Dispatch queue:
0   libsystem_kernel.dylib               0x190628764 __pthread_kill + 8
1   libsystem_pthread.dylib             0x19065fc28 pthread_kill + 288
2   libsystem_c.dylib                   0x19056dae8 abort + 180
3   libsystem_c.dylib                   0x19056ce44 __assert_rtn + 272
4   jna8074507030377149867.tmp           0x125b1404c 0x125afc000 + 98380
5   jna8074507030377149867.tmp           0x125b02d60 Java_com_sun_jna_Native_open + 320

Then this is a bug in JNA and you need to upgrade your version of JNA to 5.13.0 or higher. This crash may only seem to occur when your app is packaged, but it's not a Conveyor issue and can occur even without using it. If JNA is being used indirectly via a dependency, you can still force an upgrade by adding a direct dependency on it from your own app - Maven and Gradle will upgrade to make it a consistent version.