Gradle Docker 构建问题

Question

I have a Dockerfile with the following contents:

FROM gradle:6.9.1-jdk17 as builder
COPY services/api/build.gradle.kts ./
COPY services/api/src ./
COPY services/api/settings.gradle.kts ./
RUN gradle build --no-daemon

FROM openjdk:8-jre-slim
COPY --from=builder /home/* /home
ENTRYPOINT [ "java", "-jar", "./home/build/libs/api.jar" ]

When I copy from builder using COPY --from=builder /home/* /home it works with no issue and if I sh into the image I can see that there is a folder structure inside the home folder including build/libs/api.jar . However I want to copy just the JAR file , so I want to run COPY --from=builder /home/build/libs/api.jar . which should allow me to simply call ENTRYPOINT [ "java", "-jar", "./api.jar" ] instead of the fully qualified ENTRYPOINT [ "java", "-jar", "./home/build/libs/api.jar" ] .

Secondly, when I try running the image the container says Error: Could not find or load main class com.library.api.MainKt . So I tried building the api.jar file locally using the gradle build --no-daemon command that I am running in my dockerfile and reducing the dockerfile 's contents to simply copy that file from the local build folder (omitting the gradle build altogether) and this runs it perfectly.

I'm tearing my hair out on this issue. My gut says it's gradle not building the jar in the same way in the dockerfile as it is on my machine, but the versions are the same and I am struggling to see what else could be different.

For reference, my build.gradle.kts contents are as follows:

import org.jetbrains.kotlin.gradle.tasks.KotlinCompile

plugins {
    kotlin("jvm") version "1.4.31"
    kotlin("plugin.serialization") version "1.4.31"
}

group "com.cabanta"

repositories {
    mavenCentral()
}

dependencies {
  ...
}

tasks.withType<KotlinCompile>() {
    kotlinOptions.jvmTarget = "15"
}

tasks.withType<Jar> {
    manifest {
        attributes["Main-Class"] = "com.library.api.MainKt"
    }
    exclude("META-INF/*.RSA", "META-INF/*.SF", "META-INF/*.DSA")

    // To add all of the dependencies otherwise a "NoClassDefFoundError" error
    from(sourceSets.main.get().output)

    dependsOn(configurations.runtimeClasspath)
    from({
        configurations.runtimeClasspath.get().filter { it.name.endsWith("jar") }.map { zipTree(it) }
    })
}

If you need anything else to be able to answer, please let me know.

Thanks in advance for any help you wonderful people can give.

a final piece of pertinent information may be that my main class doesn't have a class, it simply has a main() as a function (as should be allowed in Kotlin and like I said, it builds and works when running through gradle on the local machine)

Answer 1

The issue turned out to be the way that I was copying files from local to the gradle step.

COPY services/api/build.gradle.kts ./
COPY services/api/src ./
COPY services/api/settings.gradle.kts ./

This, I have now changed to COPY services/api/* ./ , which copies all of the build files that are needed.

The API before, was being created, however it was being created without any content, which meant that Java couldn't find the class ... because it was never there in the first place.