Gradle upload a custom-generated jar file to Nexus

Do this:

apply plugin: 'maven-publish'


   publishing {
        publications {
            maven( MavenPublication ) {
                artifact theTaskThatGeneratesJar
            }
        }
        repositories {
            maven {
                def releasesRepoUrl = http://.../repositories/releases/'
                def snapshotsRepoUrl = 'http://.../repositories/snapshots/'
                url = version.endsWith('SNAPSHOT') ? snapshotsRepoUrl : releasesRepoUrl
                credentials {
                    username 'xxx'
                    password 'xxx'
                }
            }
        }

    }