For starters, I use Android Studio, which uses Gradle as the official build system, to set up all my Android projects. Make sure to download the latest version of Android Studio .

Terminology

Before we begin there is some terminology to get familiar with.

Project — A project in Android Studio represents a complete Android app. Android Studio projects consist of one or more modules. A project in Android Studio is like a workspace in Eclipse.

Module — A module is a component of your app that you can build, test, or debug independently. Modules contain the source code and resources for your app. A module in Android Studio is like a project in Eclipse

AAR — The ‘aar’ bundle is the binary distribution of an Android Library Project. (AAR Format) A Library project’s main output is an .aar package (which stands for Android archive). It is a combination of compile code (as a jar file and/or native .so files) and resources (manifest, res, assets).

Maven Central Repository — A repository provided by the Maven community. It contains a large number of commonly used libraries. Search Maven to browse the content of the central maven repository. Gradle, Please is another tool that allows you to search Maven Central. Gradle uses the jCenter repo if you included jCenter() into your repositories section (Notes about jCenter). Maven Central Repository is often referred to as Maven Central or the Central Repository.

Sonatype — Sonatype’s Open Source Software Repository Hosting (OSSRH) service is the primary avenue for project owners and contributors to publish their components to the Central Repository. It is a hosted deployment of Sonatype Nexus Professional with the Nexus Staging Suite used for the deployment process and validation, combined with a sync process to the Central Repository content delivery network. (Sonatype Producers)

GPG — GNU Privacy Guard (GPG, also GnuPG), the GNU project’s free alternative to PGP, is encryption software that’s compliant with the OpenPGP (RFC4880) standard. Using GPG you can encrypt (and decrypt) files that contain sensitive data, such as electronic protected health information (ePHI) regulated by the Health Insurance Portability and Accountability Act (HIPAA) privacy and security rules. For more on GPG, see the GNU Privacy Guard website.

Prepare your Android library

I am going to use my Trestle library as an example. There are a few modifications you need to make to your project so that it is ready to be published as a library to Maven Central.

• Separate the code that is core to the library and code that shows sample usage of the library. In my projects, I separate these out into two separate modules library and sample. Checkout out the tips on setting up a library module . You may need to rename your modules.
• In the sample module’s build.gradle file, make sure to include

apply plugin: 'com.android.application'

dependencies {
    compile project(':library')
}

• In the library module’s build.gradle file, make sure to include

apply plugin: 'com.android.library'
apply from: 'maven-push.gradle'

• In the library module, add a gradle.properties file, and make sure to include

POM_NAME=ProjectName
POM_ARTIFACT_ID=projectname
POM_PACKAGING=aar

• In the library module, add a maven-push.gradle file, and make sure to include

/*
 * Copyright 2013 Chris Banes
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

apply plugin: 'maven'
apply plugin: 'signing'

def isReleaseBuild() {
    return VERSION_NAME.contains("SNAPSHOT") == false
}

def getReleaseRepositoryUrl() {
    return hasProperty('RELEASE_REPOSITORY_URL') ? RELEASE_REPOSITORY_URL
            : "https://oss.sonatype.org/service/local/staging/deploy/maven2/"
}

def getSnapshotRepositoryUrl() {
    return hasProperty('SNAPSHOT_REPOSITORY_URL') ? SNAPSHOT_REPOSITORY_URL
            : "https://oss.sonatype.org/content/repositories/snapshots/"
}

def getRepositoryUsername() {
    return hasProperty('NEXUS_USERNAME') ? NEXUS_USERNAME : ""
}

def getRepositoryPassword() {
    return hasProperty('NEXUS_PASSWORD') ? NEXUS_PASSWORD : ""
}

afterEvaluate { project ->
    uploadArchives {
        repositories {
            mavenDeployer {
                beforeDeployment { MavenDeployment deployment -> signing.signPom(deployment) }

                pom.groupId = GROUP
                pom.artifactId = POM_ARTIFACT_ID
                pom.version = VERSION_NAME

                repository(url: getReleaseRepositoryUrl()) {
                    authentication(userName: getRepositoryUsername(), password: getRepositoryPassword())
                }
                snapshotRepository(url: getSnapshotRepositoryUrl()) {
                    authentication(userName: getRepositoryUsername(), password: getRepositoryPassword())
                }

                pom.project {
                    name POM_NAME
                    packaging POM_PACKAGING
                    description POM_DESCRIPTION
                    url POM_URL

                    scm {
                        url POM_SCM_URL
                        connection POM_SCM_CONNECTION
                        developerConnection POM_SCM_DEV_CONNECTION
                    }

                    licenses {
                        license {
                            name POM_LICENCE_NAME
                            url POM_LICENCE_URL
                            distribution POM_LICENCE_DIST
                        }
                    }

                    developers {
                        developer {
                            id POM_DEVELOPER_ID
                            name POM_DEVELOPER_NAME
                        }
                    }
                }
            }
        }
    }

    signing {
        required { isReleaseBuild() && gradle.taskGraph.hasTask("uploadArchives") }
        sign configurations.archives
    }

    //task androidJavadocs(type: Javadoc) {
    //source = android.sourceSets.main.allJava
    //}

    //task androidJavadocsJar(type: Jar, dependsOn: androidJavadocs) {
    //classifier = 'javadoc'
    //from androidJavadocs.destinationDir
    //}

    task androidSourcesJar(type: Jar) {
        classifier = 'sources'
        from android.sourceSets.main.java.sourceFiles
    }

    artifacts {
        archives androidSourcesJar
    }
}

• Modify the .gitignore file that is located at the root level of your project

# [Android] ========================
# Built application files
*.apk
*.ap_

# Files for the Dalvik VM
*.dex

# Java class files
*.class

# Generated files
bin/
gen/

# Gradle files
.gradle/
build/

# Local configuration file (sdk path, etc)
local.properties

# Proguard folder generated by Eclipse
proguard/

# Log Files
*.log


## Directory-based project format:
.idea/

## File-based project format:
*.ipr
*.iws

## Plugin-specific files:

# IntelliJ
out/

# mpeltonen/sbt-idea plugin
.idea_modules/

# JIRA plugin
atlassian-ide-plugin.xml

# Crashlytics plugin (for Android Studio and IntelliJ)
com_crashlytics_export_strings.xml


# [Maven] ========================
target/
pom.xml.tag
pom.xml.releaseBackup
pom.xml.versionsBackup
pom.xml.next
release.properties


# [Gradle-Android] ========================

# Ignore Gradle GUI config
gradle-app.setting

# Gradle Signing
signing.properties
trestle.keystore

# Mobile Tools for Java (J2ME)
.mtj.tmp/

# Package Files #
*.jar
*.war
*.ear

# virtual machine crash logs, see http://www.java.com/en/download/help/error_hotspot.xml
hs_err_pid*

# Misc
/.idea/workspace.xml
.DS_Store
/captures
**/*.iml
*.class

• Modify the settings.gradle file that is located at the root level of your project

include ':sample', ':library'

• Modify gradle.properties file which is located at the root level of your project

# Project-wide Gradle settings.

# IDE (e.g. Android Studio) users:
# Gradle settings configured through the IDE *will override*
# any settings specified in this file.

# For more details on how to configure your build environment visit
# http://www.gradle.org/docs/current/userguide/build_environment.html

# Specifies the JVM arguments used for the daemon process.
# The setting is particularly useful for tweaking memory settings.
# Default value: -Xmx10248m -XX:MaxPermSize=256m
# org.gradle.jvmargs=-Xmx2048m -XX:MaxPermSize=512m -XX:+HeapDumpOnOutOfMemoryError -Dfile.encoding=UTF-8

# When configured, Gradle will run in incubating parallel mode.
# This option should only be used with decoupled projects. More details, visit
# http://www.gradle.org/docs/current/userguide/multi_project_builds.html#sec:decoupled_projects
# org.gradle.parallel=true

VERSION_NAME=0.0.1
VERSION_CODE=1
GROUP=com.github.github_username

POM_DESCRIPTION=A library that does X, Y, and Z
POM_URL=https://github.com/github_username/ProjectName
POM_SCM_URL=https://github.com/github_username/ProjectName
POM_SCM_CONNECTION=scm:[email protected]:github_username/ProjectName.git
POM_SCM_DEV_CONNECTION=scm:[email protected]:github_username/ProjectName.git
POM_LICENCE_NAME=The Apache Software License, Version 2.0
POM_LICENCE_URL=http://www.apache.org/licenses/LICENSE-2.0.txt
POM_LICENCE_DIST=repo
POM_DEVELOPER_ID=github_username
POM_DEVELOPER_NAME=GitHub FullName

• Add a README.md to explain to other developers what your library does and how to use it. If you need to add any screenshots to your README.md I highly recommend using an app called Screenr to generate the screenshots.

Setup GPG

If you don’t already have GPG installed on your machine then you will need to download it. On MacOSX, here are the install commands .

If you never used it — first create the GPG keys:

$ gpg --gen-key

If you aren’t sure what to answer to the questions when creating the GPG keys this guide should help (Creating an encryption key) .

Next, find your key ID :

$ gpg --list-keys

There the first line will be like pub XXXXX/YYYYYYYY <date>. Remember that ‘YYYYYYYY’ part, it’s you key ID.

Now, publish your keys:

$ gpg --keyserver hkp://keyserver.ubuntu.com --send-keys YYYYYYYY
$ gpg --keyserver hkp://pgp.mit.edu --send-keys YYYYYYYY

You may use other key servers as well. You may also want to ensure your keys were published:

$ gpg --keyserver hkp://pgp.mit.edu --search-keys [email protected] # Use your email