Release an Android Library on Maven Central

I was going to put “the easy way”, but well the reality is that there is no easy way. Hopefully this post can make the entire experience a bit less painful for you.

You will need the following ingredients

An Android library
An account on sonatype
A gpg key
A gradle build script
Lot’s of gradle configuration
Perform the release steps on sonatype

I’m going to assume that you have a library in a releasable state and go straight to step 2

Create a sonatype account

The first thing you need to do is create an account on https://issues.sonatype.org. This involves the standard fare of picking a username and a password. Once that is done, you can create an issue to provision your account and obtain a groupId.

On any other website you would be done now, but sonatype verifies your account manually and this takes some time. Don’t expect to release your library the day you create your account.

Make sure you read and follow the guidlines for the groupId, they are strictly enforced. If it is a reversed fully qualified domain name of a domain you own (eg: com.wdullaer for me) or where they can reasonably expect your project to live under your control (eg: com.github.wdullaer), you should be fine.

Create a gpg key

On Linux the gpg or gpg2 binaries should be installed by default. If not use your systems package manager to get them. I used gpg instead gpg2, because the latter version kept complaining about gnome-keyring, but they should functionally be the same.

Run gpg --gen-key
The default values for all the parameters should be fine. Fill out your email address, name and optional comment (nickname).
If gpg complains about insufficient memory, run the find / > /dev/null in a separate shell while gpg is running

Once the key is created, you’ll see something like.

gpg: key 1332E476 marked as ultimately trusted
public and secret key created and signed.

gpg: checking the trustdb
gpg: 3 marginal(s) needed, 1 complete(s) needed, PGP trust model
gpg: depth: 0  valid:   4  signed:   0  trust: 0-, 0q, 0n, 0m, 0f, 4u
pub   2048R/1332E476 2014-12-16
Key fingerprint = 4709 0122 F4F9 466A 9E60  CCAC B0E4 98EA 1332 E476
uid                  Wouter Dullaert <[email protected]>
sub   2048R/DFEF78B0 2014-12-16

Here you should get your key-ID, which in this example is: 1332E476

Upload this key to a keyserver (any will do, they sync among themselves)
```
gpg --keyserver hkp://pool.sks-keyservers.net --send-keys 1332E476
```

Dump both the public and private keys to file and back them up somewhere safe

gpg -ao gpg_public.key --export 1332E476
gpg -ao gpg_private.key --export-secret-keys 1332E476

More information can be found here: http://central.sonatype.org/pages/working-with-pgp-signatures.html

Get the gradle build script

This is in fact the easiest step. Maven Central puts a lot of quality requirements on the artifacts you can upload: pom.xml files, javadocs, etc.

However, someone already went through the trouble of creating a proper Maven release build script at https://raw.githubusercontent.com/chrisbanes/gradle-mvn-push/master/gradle-mvn-push.gradle This script takes care of preparing your artifact in a Maven Central compatible fashion and uploads it to your staging repository.

You can include this one directly into the root of your build.gradle of your library.

apply from: 'https://raw.github.com/chrisbanes/gradle-mvn-push/master/gradle-mvn-push.gradle'

Or if you’re the paranoid sort: you can add a hardcopy to your project and reference that.

Configure gradle

You will need to create a total of 3 gradle.properties files to configure the build script you added in the previous step:

1 at the module level (/MyAwesomeLibrary/library/gradle.properties)

POM_NAME=SwipeActionAdapter
POM_ARTIFACT_ID=swipeactionadapter
POM_PACKAGING=aar

1 at the project level (/MyAwesomeLibrary/gradle.properties)

VERSION_NAME=1.3.0
VERSION_CODE=5
GROUP=com.wdullaer

ANDROID_BUILD_MIN_SDK_VERSION=14
ANDROID_BUILD_TARGET_SDK_VERSION=21
ANDROID_BUILD_SDK_VERSION=21
ANDROID_BUILD_TOOLS_VERSION=21.1.1

POM_DESCRIPTION=Android Swipe Action Adapter
POM_URL=https://github.com/wdullaer/SwipeActionAdapter
POM_SCM_URL=https://github.com/wdullaer/SwipeActionAdapter
POM_SCM_CONNECTION=scm:[email protected]:wdullaer/SwipeActionAdapter.git
POM_SCM_DEV_CONNECTION=scm:[email protected]:wdullaer/SwipeActionAdapter.git
POM_LICENCE_NAME=Apache v2
POM_LICENCE_URL=https://github.com/wdullaer/SwipeActionAdapter/blob/master/LICENSE
POM_LICENCE_DIST=repo
POM_DEVELOPER_ID=wdullaer
POM_DEVELOPER_NAME=Wouter Dullaert

1 in your gradle home folder. (~/.gradle/gradle.properties)

signing.keyId=1332E476
signing.password=<your_gpg_key_password>
signing.secretKeyRingFile=/home/wdullaer/.gnupg/secring.gpg

NEXUS_USERNAME=<your_sonatype_username>
NEXUS_PASSWORD=<your_sonatype_password>

Strictly speaking you could add all the variables to the lowest level, but if we’re going through all this hassle we might as well do it properly.

Release the staged artifact

Once you have uploaded your artifact to Maven Central using the build script you need to release it.

Go to http://oss.sonatype.org and login with the account you created in step 1.
Initially your artifact is located in a so called “staging” repository. It’s name is your groupId with a dash and some numbers.
Like all proper enterprise software there is a whole bunch of other options and data shown here, that are totally irrelevant, which you should under no condition touch.
Once you’ve located your staging repository you can press the close button. This won’t actually close the repository but triggers a process that checks whether the contents of the repository meets sonatype’s guidelines.
After a few seconds this process should be finished and you can hit the refresh button.
If your repository passes the tests. It will be marked closed and you should be able to click the release button. This will terminate the process and make your library publicly available.

Your users can now access your library by putting the following line in their build.gradle dependencies:

compile 'com.wdullaer:materialdatetimepicker:1.0.0'

More information on this last step can be found here: http://central.sonatype.org/pages/releasing-the-deployment.html

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