SpringBoot resolveMainClassName fails when building with Gradle using Java 22

It fails like this:

Caused by: java.lang.IllegalArgumentException: Unsupported class file major version 66
        at org.springframework.asm.ClassReader.<init>(ClassReader.java:199)
        at org.springframework.asm.ClassReader.<init>(ClassReader.java:180)
        at org.springframework.asm.ClassReader.<init>(ClassReader.java:166)
        at org.springframework.asm.ClassReader.<init>(ClassReader.java:287)
        at org.springframework.boot.loader.tools.MainClassFinder.createClassDescriptor(MainClassFinder.java:254)
        at org.springframework.boot.loader.tools.MainClassFinder.doWithMainClasses(MainClassFinder.java:136)
        at org.springframework.boot.loader.tools.MainClassFinder.findSingleMainClass(MainClassFinder.java:109)
        at org.springframework.boot.gradle.plugin.ResolveMainClassName.findMainClass(ResolveMainClassName.java:145)
        at org.springframework.boot.gradle.plugin.ResolveMainClassName.resolveMainClassName(ResolveMainClassName.java:139)
        at org.springframework.boot.gradle.plugin.ResolveMainClassName.resolveAndStoreMainClassName(ResolveMainClassName.java:124)

This can be worked around by configuring the application's main class name:

springBoot {
    mainClass = 'com.example.ExampleApplication'
}

Comment From: sergey-morenets

Hi @wilkinsona

I encountered the same issue while trying to upgrade to JDK 22. Do you have ETA for the fixes?

Comment From: wilkinsona

Not at this time, I'm afraid. Please use the workaround for now.

Comment From: Eng-Fouad

What about resolveTestMainClassName (run with bootTestRun)? Is there a workaround?

Comment From: Eng-Fouad

I found a workaround for resolveTestMainClassName:

tasks.getByName<org.springframework.boot.gradle.plugin.ResolveMainClassName>("resolveTestMainClassName") {
    configuredMainClassName.set("io.fouad.tests.TestAppLauncher")
}

Comment From: mhalbritter

Cause for this is that we downgrade Spring Core in the spring-boot-loader-tools to 6.0.10 to workaround a Gradle limitation with multi-version JAR files.

The ClassReader from Spring Framework 6.1 supports Java 22.