How to set packaging to pom in Gradle instead of defaulting to jar - maven

Question

I have a project that generates a Bill of Materials (BOM). When I execute gradle build it generates an empty jar, containing only a META-INF folder.
However I am able to publish the pom (BOM) to Nexus correctly, with the side effect of also uploading the empty jar.
According to the maven plugin doc https://docs.gradle.org/current/userguide/maven_plugin.html we should be able to set the packaging:
packaging archiveTask.extension
Here, uploadTask and archiveTask refer to the tasks used for uploading
and generating the archive
How can I set the packaging to pom?
Example of Gradle uploaded pom:
<project xmlns="http://maven.apache.org/POM/4.0.0" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<modelVersion>4.0.0</modelVersion>
<groupId>com.ttt.a</groupId>
<artifactId>my-bom</artifactId>
<version>Something-SNAPSHOT</version>
When I upload it with maven instead of gradle, there is an additional:
<packaging>pom</packaging>
UPDATE:
Full build.gradle config:
buildscript {
repositories {
maven {
url "http://myrepo"
}
}
dependencies {
classpath "io.spring.gradle:dependency-management-plugin:1.0.4.RELEASE"
classpath "org.sonarsource.scanner.gradle:sonarqube-gradle-plugin:2.5"
classpath 'org.asciidoctor:asciidoctor-gradle-plugin:1.5.7'
} }
apply plugin: 'java' apply plugin: 'maven' apply plugin: "io.spring.dependency-management" apply plugin: "jacoco" apply plugin: 'org.asciidoctor.convert' apply plugin: 'org.sonarqube'
group = project.properties['groupId'] version = project.properties['version'].toString()
description = """Bill of Materials"""
sourceCompatibility = 1.8 targetCompatibility = 1.8
ext {
xxx = '1.0.0'
yyy = '1.2.0'
... }
repositories {
maven {
url "http://myrepo"
} }
dependencyManagement {
dependencies {
dependency "com.myorg:xxx:${xxx}"
dependency "com.myorg:yyy:${yyy}"
...
} }
uploadArchives {
repositories {
mavenDeployer {
snapshotRepository(url: 'http://myrepo') {
authentication(userName: "$System.env.NEXUS_USER", password: "$System.env.NEXUS_PASSWORD")
}
}
} }
asciidoctor {
sourceDir = file('src/docs/asciidoc/')
sources {
include '*.adoc'
}
outputDir = file("build/docs/${version}") }
task generateDummyBom {
doLast {
project.buildDir.mkdirs()
new File("$project.buildDir/dummy.pom").write("<project></project>\n")
}
ext.bomFile = file("$project.buildDir/dummy.pom") }
artifacts {
archives(generateDummyBom.bomFile) {
builtBy generateDummyBom
} }
jar.enabled = false

Answer 1

I found that the maven plugin seems to ignore the packaging property. After some experimentation, I found that it sets the packaging property to the extension of the file in your artifact. So, the way to get the packaging property set to pom is to create a dummy artifact with a file having a .pom extension, as below.
// The real file that we want to publish is the pom generated implicitly by the
// maven publishing plugin.
//
// We need to generate at least one file that we can call an archive so that the
// maven plugin will actually publish anything at all. Luckily, if the file
// that we call an archive is a .pom file, it's magically discarded, and we are
// only left with the implicitly-generated .pom file.
//
// We need the extension of the file to be `.pom` so that the maven plugin will
// set the pom packaging to `pom` (i.e. `<packaging>pom</packaging>`). Otherwise,
// packaging would be set to `xml` if our only file had an `.xml` extension.
task generateDummyBom {
doLast {
// Since we don't depend on anything else, we have to create the build dir
// ourselves.
project.buildDir.mkdirs()
// The file actually has to have xml in it, or Sonatype will reject it
new File("$project.buildDir/${project.artifactId}.pom").write("<project></project>\n")
}
ext.bomFile = file("$project.buildDir/${project.artifactId}.pom")
}
artifacts {
archives(generateDummyBom.bomFile) {
builtBy generateDummyBom
}
}
jar.enabled = false
Update: If you apply the java plugin, you will need to remove the jar archive from your archives.
// Remove the default jar archive which is added by the 'java' plugin.
configurations.archives.artifacts.with { archives ->
def artifacts = []
archives.each {
if (it.file =~ 'jar') {
// We can't just call `archives.remove(it)` here because it triggers
// a `ConcurrentModificationException`, so we add matching artifacts
// to another list, then remove those elements outside of this iteration.
artifacts.add(it)
}
}
artifacts.each {
archives.remove(it)
}
}
Second update: Replaced "dummy.pom" with "${project.artifactId}" above.

Answer 2

I couldn't get Garrett's solution to work, but I did have success like this:
dependencies {
// ...Omitted...
}
tasks.named('generatePomFileForMavenJavaPublication') {
pom.with {
description = 'Parent BOM'
withXml {
// ...Omitted...
}
}
}
// Removing all jar artifacts from the mavenJava publication
// appears to automagically cause packaging to be set to 'pom'!
publishing.publications.named('mavenJava') {
artifacts.removeIf { artifact ->
artifact.extension == 'jar'
}
}