Can I create a Maven POM-only (BOM) build using the Gradle maven plugin to be deployed to Nexus?

Question

I have a Gradle project which uses Spring's dependency management plugin to define a list of dependency versions. I am also using the Maven plugin to deploy the project to a Maven repository.

I would like to be able to deploy this as a Maven bill of materials (BOM) so that I can use it in other Gradle projects to define my dependency versions. I have been able to get this to work so long as I also deploy a JAR file. However, the JAR is completely empty and superfluous. My goal is to generate and deploy just the POM file, like I would be able to do if this were a Maven project with a "pom" packaging.

If I manually exclude the JAR from the list of artifacts to be published, then nothing gets installed, not even the POM file.

This is a test build to demonstrate the issue:

group 'test'
version '1.0.0-SNAPSHOT'

buildscript {
  repositories {
    mavenCentral()

  }
  dependencies {
    classpath 'org.springframework.boot:spring-boot-gradle-plugin:1.5.1.RELEASE' //Matches the Spring IO version
  }
}

apply plugin: 'java'
apply plugin: 'io.spring.dependency-management'
apply plugin: 'maven'

dependencyManagement {
  dependencies {
    dependency 'cglib:cglib-nodep:3.2.4'
    dependency 'junit:junit:4.12'
  }
}

////Uncommenting this causes nothing at all to be deployed:
//jar.enabled = false
//configurations.archives.artifacts.with { archives ->
//  archives.removeAll { it.type == 'jar' }
//}

The above correctly produces and installs the following POM file into my local Maven repo:

<?xml version="1.0" encoding="UTF-8"?>
<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>test</groupId>
  <artifactId>gradle-pom-packaging-test</artifactId>
  <version>1.0.0-SNAPSHOT</version>
  <dependencyManagement>
    <dependencies>
      <dependency>
        <groupId>cglib</groupId>
        <artifactId>cglib-nodep</artifactId>
        <version>3.2.4</version>
      </dependency>
      <dependency>
        <groupId>junit</groupId>
        <artifactId>junit</artifactId>
        <version>4.12</version>
      </dependency>
    </dependencies>
  </dependencyManagement>
</project>

However, it also installs a JAR file that is empty save for the MANIFEST.MF file.

I was able to successfully get this working using the maven-publish plugin. However, I'm also making use of the Gradle Sonatype Nexus plugin to publish the artifact to a Nexus instance. As this builds upon the maven plugin, the maven-publish plugin will not work for my needs. The following is all I needed to add to get it working with the maven-publish plugin:

apply plugin: 'maven-publish'
publishing {
  publications {
    maven(MavenPublication) {
    }
  }
}

Is there a way to generate and deploy just the POM file using the maven Gradle plugin, like I would be able to do if this were a Maven project with a "pom" packaging?

Answer 1

In Gradle 6+ versions, we can use Gradle Java Platform Plugin to publish a maven-bom without many configurations and scripting.

group 'test.platform.simple.bom'
version '1.0.0-SNAPSHOT'

repositories {
    maven {
        mavenCentral()
    }        
}

apply plugin: 'java-platform'
apply plugin: 'maven-publish'

javaPlatform {
    allowDependencies()
}

dependencies {
    constraints {
        api 'junit:junit:4.12'
        api 'cglib:cglib-nodep:3.2.4'
        // runtime 'org.postgresql:postgresql:42.2.5' <-- runtime constraint
        // api project(":core") <-- constraint from local project
    }

    // api platform('com.fasterxml.jackson:jackson-bom:2.9.8') <-- constraint from another platform
}

publishing {
  publications {
    maven(MavenPublication) {
      from components.javaPlatform
    }
  }
}

Dependencies to be managed can be defined under dependencies as api or runtime constraints. Constraints can be utilized to manage dependencies from a local project as well as from another platform/bom. Please note that we need to configure a Maven publication that uses the javaPlatform component to get it published as a maven bom artifact.

Answer 2

Tha acdcjunior's answer can be improved a little. Dependencies in the build.gradle can by declared in the standard dependencies section. Also, in pom.xml of a BOM versions should be declared in dependencyManagement section:

plugins {
    id 'java-library'
    id 'maven-publish'
}

group = 'com.example'
version = '1.0.0'

repositories {
    mavenCentral()
}

dependencies {
    api 'org.apache.commons:commons-lang3:3.9'
    api 'org.postgresql:postgresql:42.2.11'
}

publishing {
    repositories {
        maven {
            url = "$nexusUrl"
            credentials {
                username = "$nexusUsername"
                password = "$nexusPassword"
            }
        }
    }

    publications {
        maven(MavenPublication) {
            groupId = "${project.group}"
            artifactId = "${project.name}"
            version = "${project.version}"

            pom.withXml {
                asNode().children().last() + {
                    resolveStrategy = Closure.DELEGATE_FIRST

                    name 'My BOM'
                    description 'My Bill of Materials (BOM)'

                    dependencyManagement {
                        dependencies {
                            project.configurations.each { conf ->
                                conf.dependencies.each { dep ->
                                    dependency {
                                        groupId "${dep.group}"
                                        artifactId "${dep.name}"
                                        version "${dep.version}"
                                    }
                                }
                            }
                        }
                    }
                }
            }
        }
    }
}

The resulting pom.xml can be published to Nexus with the command

./gradlew clean build publish -i

or to a local Maven repo (~/.m2/repository)

./gradlew clean build pTML -i

This notation is not only shorter but also allows processing dependencies. For example, perform vulnerabilities scanning using OWASP Dependency-Check plugin:

plugins {
    //...
    id 'org.owasp.dependencycheck' version '5.3.0'
}

dependencyCheck {
    failBuildOnCVSS = 9 //Critical Severity
}

check.dependsOn dependencyCheckAnalyze

Answer 3

You could have a build.gradle such as:

apply plugin: 'maven-publish'
apply plugin: 'signing'

publishing {
    repositories {
        maven {
            def releasesRepoUrl = "https://oss.sonatype.org/service/local/staging/deploy/maven2/"
            def snapshotsRepoUrl = "https://oss.sonatype.org/content/repositories/snapshots/"
            url = version.endsWith('SNAPSHOT') ? snapshotsRepoUrl : releasesRepoUrl
            credentials {
                username ossrhUsername
                password ossrhPassword
            }
        }
    }

    publications {
        maven(MavenPublication) {
            groupId = 'com.example.id'
            artifactId = 'my-artifact-id'
            version = '1.0.0'

            pom.withXml {
                asNode().children().last() + {
                    resolveStrategy = Closure.DELEGATE_FIRST

                    name 'My Lib Name'
                    description 'My Lib Description'
                    url 'https://example.com/id/lib'

                    licenses {
                        license {
                            name 'The Apache License, Version 2.0'
                            url 'http://www.apache.org/licenses/LICENSE-2.0.txt'
                        }
                    }
                    scm {
                        connection 'scm:git:[email protected]:acdcjunior/lib/id.git'
                        developerConnection 'scm:git:[email protected]:acdcjunior/lib/id.git'
                        url '[email protected]/id.git'
                    }
                    developers {
                        developer {
                            id 'someone'
                            name 'Someone Name'
                            email '[email protected]'
                        }
                    }
                    dependencies {
                        dependency {
                            groupId 'com.example.other'
                            artifactId 'some-dependency'
                            version '1.0.0'
                        }
                        dependency {
                            groupId 'org.apache.commons'
                            artifactId 'commons-lang3'
                            version '3.9'
                        }
                    }
                }
            }
        }
    }
}

signing {
    sign publishing.publications.maven
}

Example of a project using this: https://github.com/acdcjunior/domain-id/blob/master/domain-id-all/build.gradle

Answer 4

You should consider that plugin which has a DSL to create BOMs the gradle way :

https://github.com/xvik/gradle-pom-plugin

Julien