Launch4J build not launching

[cancech]

I have successfully ported my desktop application from Dagger/Spring to Micronaut/Spring (there's just way too much Spring code in there for me to be able strip it all out in a timely manner). Using Micronaut and PicoCLI everything is working beautifully in Eclipse/Gradle. It's launching, tests are passing, so now I want to do a build and install it to make sure that everything will work for our customer.

Our build (via Gradle) uses Shadow (com.github.johnrengelman.shadow) to combine our application with all of its dependencies into a single Jar file. I've checked and all expected dependencies appear to be present, and from the look of it the generated Micronaut classes are also present in the shadow jar. We then use Launch4J to make this shadow jar executable. From everything that I can tell, the output from Launch4J looks to be correct, however when I try to run it the splash screen appears for a fraction of a second and that's it. When I run the Launch4J generated executable as a jar file, I get the following:

Error: An unexpected error occurred while trying to open file My App.exe

The Launch4J debug information I've been able to collect all looks correct (other than an Exit Code of 1), and all of my attempts at digging into this have proven to be fruitless thus far. I gather that the most common causes of this error are invalid MANIFEST.MD in the jar (I've checked and it's identical to the original pre-Micronaut manifest), or issues with the classpath (the shadow jar should contain all of the required dependencies, and no other classpath references are used as far as I can tell). The relevant portions of the build.gradle are as follows:

task createExe(type: Launch4jLibraryTask) {
    jarTask = shadowJar
    icon = "${projectDir}/src/main/installer/nsis/Icon.ico"
    outfile = "${appName}.exe"
    copyConfigurable = files {}
    stayAlive = 'true'
    bundledJrePath = 'jre'
    bundledJre64Bit = true
    jvmOptions = [
            '-Xmx1024m',
            '-Dsun.java2d.d3d=false'
    ]
    fileDescription = appName + ' Application'
    productName = appName
    internalName = appName
    copyright = 'My Company'
    companyName = 'My Company'
}

jar {
    manifest {
        attributes(
                'Main-Class': mainClassName,
                'SplashScreen-Image': 'images/Z006BASSPS.jpg'
        )
    }
}

shadowJar {
    dependsOn replaceTokens
    zip64 true
    mergeServiceFiles() {
        exclude 'META-INF/services/org.xmlpull.v1.XmlPullParserFactory'
    }
    append 'META-INF/spring.factories'
    append 'META-INF/spring.handlers'
    append 'META-INF/spring.schemas'
    append 'META-INF/spring.tooling'
}

None of which has been changed since pre-Micronaut.

Is Micronaut compatible with Launch4J? Is there something special that needs to be done/added that I'm missing here? Has there been any attempt or success using Micronaut with Launch4J?

[cancech]

I've finally figured out the problem, and posting the answer here to help any who may be interested. The issue turned out to have nothing to do with Micronaut or compatibility issues between Micronaut and Launch4j, but rather a seeming limitation within Launch4j when working with jar files that contain too many files. The migration to Micronaut pushed the number of files beyond the 32-bit jar limit of 65535, necessitating adding the zip64 true flag as seen above. However, once that limit is passed Launch4j breaks, and I wasn't able to find any means of settings an equivalent zip64 flag on it. In fact I found virtually no information in terms of Launch4j file count limitations (so the limit may not even be 65535, I have no way of verifying if that is indeed the limit).

My solution is to turn on the dontWrapJar flag, so that Launch4j generates a tiny executable which then launches the generated shadow jar. This changes the packaging to require including the shadow jar in a lib directory when deploying, but at least it works! The updated createExe task is as follows:

task createExe(type: Launch4jLibraryTask) {
    jarTask = shadowJar
    dontWrapJar true // <<<<< THIS IS THE ADDED LINE
    icon = "${projectDir}/src/main/installer/nsis/Icon.ico"
    outfile = "${appName}.exe"
    copyConfigurable = files {}
    stayAlive = 'true'
    bundledJrePath = 'jre'
    bundledJre64Bit = true
    jvmOptions = [
            '-Xmx1024m',
            '-Dsun.java2d.d3d=false'
    ]
    fileDescription = appName + ' Application'
    productName = appName
    internalName = appName
    copyright = 'My Company'
    companyName = 'My Company'
}