As mentioned in a previous article, writing and publishing an open-source library is good for a lot of reasons.

There are a few things to do in order to make sure the publication of your library makes sense, here is how to do that in Java.

Open sourcing

My library is here. The issues are public and anyone can add one.

The shields on the readme page also indicate the public status of the testing, code coverage, and publication.

Testing

For testing, I use JUnit. It is the most common testing framework for plain Java.

To ensure that the tests are always run, I integrated the project with a continuous integration server. I chose Travis CI because it integrates easily with GitHub. All is required is the .travis.yml file with the language declaration and the which JDK to use.

language: java
jdk: oraclejdk8

Whenever a commit is pushed on a branch, Travis pulls it, compiles it, runs the tests, and reports the result to GitHub. It ensures that you always know immediately when a branch does not compiles, or fails any test.

Coverage

JaCoCo is a code coverage library for Java. It generates XML and HTML reports based on the tests integrated in your project. It has a Gradle plugin, which adds a jacocoTestReport task. I add this task as a dependency of the check task, which already encompasses the test task, and is run by the CI server.

apply plugin: 'jacoco'

jacocoTestReport {
    reports {
        xml.enabled = true
        html.enabled = true
    }
}
check.dependsOn jacocoTestReports

To make sense of the report, and to automatize the validation, I integrate Codecov. Again, pretty easy, just send the result of the tests to Codecov using their provided script.

after_success:
  - bash <(curl -s https://codecov.io/bash)

You can then access other features, such as comparing the coverage from a branch to another, or rapidly see which parts of a pull request are not being tested. This is particularly important if you receive outside contributions to your project.

Publication

Gradle build system uses Maven dependency management system, and connects to any maven repository. The most common are Maven Central and jCenter. I use jCenter because it is included by default in Android Studio in new Android projects.

To publish on jCenter, here is how

Get an API key

1. Register on Bintray
2. Get your API key from your profile
3. Add your username and API key to a file that you add to your .gitignore. The key is obviously secret and should not be shared with anyone.

bintray.user=smaspe
bintray.apikey=API key goes here

Prepare the package

Publishing on jCenter requires that you include the JavaDoc and the source together with the build. There are a few things to add to your build file.

1. Include the maven and maven-publish plugins
2. To actually create the JavaDoc and the source bundle, define the javadocJar and sourcesJar tasks
3. Declare those tasks as being archives in the artifacts of the publication
4. Configure the group and version of your library

group 'com.example.group'
version 'X.Y.Z'

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

task javadocJar(type: Jar, dependsOn: javadoc) {
    classifier = 'javadoc'
    from 'build/docs/javadoc'
}

task sourcesJar(type: Jar) {
    from sourceSets.main.allSource
    classifier = 'sources'
}

artifacts {
    archives javadocJar
    archives sourcesJar
}

Uploading

1. Get the jCenter plugin
2. Read the properties file with your API key
3. Configure the bintray task

plugins {
    id "com.jfrog.bintray" version "1.4"
}

Properties properties = new Properties()
try {
    properties.load(project.rootProject.file('local.properties').newDataInputStream())
} catch (Exception ignored) {}

bintray {
    user = properties.getProperty("bintray.user")
    key = properties.getProperty("bintray.apikey")

    configurations = ['archives']
    pkg {
        repo = "maven"
        name = "The name of your library"
        publish = true
        // There are other parameters you can set, but only those are mandatory
    }
}

You now only have to call the tasks whenever you want to publish a new version

./gradlew bintrayUpload

That’s about it. Refer to my complete Gradle file to see the complete configuration I use.