During the android workshop, in the office and in the chat with some of the android developers, I have received some questions around build script and repository:
- Why earlier versions of android studio were using maven central?
- Why android project, getting created using android studio, is using jcenter?
- What are the reasons/benefits/purpose that android studio has gone with JCenter repository?
- JCenter Vs. Maven central
I had shared some of the points at that time, but I tried to go into the deep to know more about the migration made from maven central to jcenter. I have found interesting details from the couple of links:
- http://stackoverflow.com/questions/24852219/android-buildscript-repositories-jcenter-vs-mavencentral
- https://code.google.com/p/android/issues/detail?id=72061
- https://news.ycombinator.com/item?id=8099840
- http://blog.bintray.com/2014/02/11/bintray-as-pain-free-gateway-to-maven-central/
Before going ahead and we discuss about the migration made from maven central to jcenter, here is brief about the repository (in case if you really don’t know!)
What is repository?
In Maven terminology, a repository is a place i.e. directory where all the project jars, library jar, plugins or any other project specific artifacts are stored and can be used by Maven easily.
In build.gradle file, you need to specify which repository to use when resolving dependencies for building your project, so you need to put something like the following in your build.gradle file:
repositories {
jcenter()
}
Yes, you need to specify at least one repository before you use any external dependency. Read more about Dependency Management Basics and repositories.
Maven central to jcenter migration
Now, here are the details and interesting points about the jcenter and the transition made from maven central to jcenter:
- As said earlier, jcenter is the new default repository used with Android’s gradle plugin.
- jcenter is a Java repository in Bintray, which is the largest repo in the world for Java and Android OSS libraries, packages and components.
- All the content in jcenter is served over a CDN, with a secure https connection. Where as the central maven 2 repository is HTTP only and HTTPS is not supported. Reference: 51.6.2. Maven central repository. (This might be one of the reasons as Google is a fan of HTTPs!).
- jcenter() is a superset of mavenCentral(), that encompasses many additional repositories and artifacts. Reference: Blog @ Bintray.
- The jcenter guys claim, that they have a better performance than maven central.
- Bintray has a different approach to package identification than the legacy Maven Central.
- If you really need to get your package to Maven Central (for supporting legacy tools) you can do it from Bintray as well, in a click of a button or even automatically.
Regarding performance improvements, couple of android developer advocates had faced/noticed the issue of huge indexing with maven central.
In the words of Tor Norbye:
I ran AndroidStudio with a brand new settings directory, so it went and connected maven central and downloaded an index of the available artifacts.
Then I happened to look at the size of my directory.
My ~/Library/Cache/AndroidStudioPreview is 1.5G, and 1.2G of those are taken by the “Maven” subdirectory.
That’s ridiculous. We barely use the index at all. The primary use for it is the Dependency editor in the Project Structure Dialog, but we really don’t need to have a precomputed index for it. MavenCentral has a fast online JSON search we can use on demand when somebody searches for artifacts. In https://android-review.googlesource.com/#/c/94843/ we added a lint check which checks whether the dependencies are up to date, and the search for a handful of artifacts is near instant.
In short, we really don’t need the cache; it may help with code completion in .gradle and maven .pom files, but that’s not a super important usecase, and certainly not something *all* users should have to sacrifice 1.5G of download speed and diskspace to have the possibility of one day doing.
Read more on: The Maven index is *huge*!
I must say, after this migration from maven cetnral to jcenter, performance of the android studio is noticeable. Earlier loading android studio in even 4GB RAM configuration laptop, was all like:
Any way, this is not the ending of this study here, I still want to know more about the improvements or strong points (if any). If you know or have played enough with jcenter and maven central, please share your inputs. And also, as this is almost an undocumented point, I am really looking forward to hear about this migration, from the android developers advocates or engineers working in android tools team.
