Working gradle script for bintray and maven central upload

build.gradle

// This is working gradle script for uploading artifacts of the given project
// to bintray/jcenter and to maven central (via bintray "sync to maven central" function).
// This script can be included from other scripts via `apply from: 'filename'` syntax.

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

import org.gradle.api.internal.artifacts.publish.DefaultPublishArtifact

version = '1.0.0'
description = 'Project description goes here'

ext {
  project_id = 'MyProjectId'
  developer_id = 'developer1'
  developer_name = 'Full Developer Name'
  project_website = "https://github.com/${developer_id}/${project_id}"
  project_scm = "scm:git@github.com:${developer_id}/${project_id}.git"
  license = 'Apache 2.0 License'
  license_url = "https://raw.github.com/${developer_id}/${project_id}/master/LICENSE"
}

install.repositories.mavenInstaller.pom*.whenConfigured { pom ->
  pom.project {
    name project.name
    packaging 'jar'
    description project.description
    url project.project_website

    scm {
      url project.project_scm
      connection project.project_scm
      developerConnection project.project_scm
    }

    licenses {
      license {
        name project.license
        url project.license_url
        distribution 'repo'
      }
    }

    developers {
      developer {
        id project.developer_id
        name project.developer_name
      }
    }
  }
}

def thisProject = project
bintray {
  // hasProperty to make Gradle happy when bintrayXXX properties are not defined 
  // and we don't call any bintray tasks.
  user = thisProject.hasProperty('bintrayUser') ? thisProject.bintrayUser : ''
  key = thisProject.hasProperty('bintrayKey') ? thisProject.bintrayKey : ''
  configurations = ['archives']
  pkg {
    repo = 'maven'
    name = thisProject.rootProject.project_id
    desc = thisProject.rootProject.description
    licenses = [ thisProject.rootProject.license ]
    labels = [ 'label1', 'label2' ]
  }
  dryRun = false
}

bintrayUpload {
  doFirst {
    // here we sign every archives artifact, then add all signature files to artifacts
    // (not needed for jcenter upload, needed for maven central upload)
    def signatureArtifacts = []
    collectArtifacts(project.configurations.archives).each { a ->
      def s = signing.sign(a.file)
      s.signatureFiles.each { f ->
        def fname = f.name
        def ext = fname.substring(fname.lastIndexOf('.') + 1)
        signatureArtifacts.add(new DefaultPublishArtifact(a.name, a.extension + '.' + ext, ext, a.classifier, new Date(), f, [] as Object[]))
      }
    }
    project.configurations.archives.artifacts.addAll(signatureArtifacts)
  }
}