TL;DR version

If you can't find a library (Maven dependency) you need for your project after Bintray/JCenter (or another similar service) shutdown, but you still have it in your local Gradle cache, you can easily set up your own local Maven repository with that library as a replacement and keep the files for as long as you need (see "Finding the cached dependencies in Gradle cache" and "Setting up a local Maven repository" paragraphs for the details).

Just a little context

A few months ago JFrog announced it is sunsetting some of its services, including Bintray and JCenter, where a lot of dependencies are hosted. According to MvnRepository, there are 841,529 indexed jars on JCenter and its popularity has been increasing very rapidly over the recent years 🚀

A surprising turn of events

Bintray and JCenter shutdown was planned on May 1st, 2021, although on April 27th, JFrog updated their original announcement, stating that they "will keep JCenter as a read-only repository indefinitely". It sounds very comforting yet, in spite of that, I couldn't access a few dependencies anymore. I think some of them were hosted on JCenter, at least according to MvnRepository, so it surprised me quite a bit, but maybe I had some additional issues, possibly a misconfiguration like a wrong order of the repositories declarations in Gradle (can't remember now 😅).

Anyway, since some of my dependencies were hosted on Bintray as well, I decided it would be better to simply migrate away from both Bintray and JCenter. So I tried, and I failed quite miserably at first, which lead me to an uncommon solution to this problem.

Theory vs practice

When you read some blog posts and articles about the planned Bintray/JCenter shutdown and migration paths, they all claim you can simply switch over to a different Maven repository (preferably, Maven Central). What they usually don't mention is that you can consider yourself really lucky if you succeed.

In many cases, you will find it impossible to switch over for some reason, e.g. either there is no other Maven repository hosting the libraries you need, or it will turn out the library authors planned a migration only for the newer or upcoming releases of their libraries. Sometimes updating the dependency version doesn't cause much trouble, especially if it's your direct dependency you are familiar with and if it's backward compatible. It becomes much harder when these dependencies are transitive or when their newer versions turn out to require a lot of additional work on the client's side.

When I reviewed all the unresolvable dependencies, it became clear to me it's not going to be like a walk in the park but quite the opposite.

How to find all the missing dependencies at once

Even though I was still able to build my project locally thanks to Gradle cache, the automated continuous integration builds on TeamCity were failing (and it's also how I found out about the problem in the first place) with errors like:

> Could not resolve com.datadoghq:dd-sdk-android:1.5.1.
  Required by:
      project :app > project :datadog
   > Could not resolve com.datadoghq:dd-sdk-android:1.5.1.
      > Could not get resource 'https://dl.bintray.com/datadog/datadog-maven/com/datadoghq/dd-sdk-android/1.5.1/dd-sdk-android-1.5.1.pom'.
         > Could not GET 'https://dl.bintray.com/datadog/datadog-maven/com/datadoghq/dd-sdk-android/1.5.1/dd-sdk-android-1.5.1.pom'. Received status code 403 from server: Forbidden

Running the following command allowed me to find all the unresolvable dependencies quickly:

./gradlew :app:dependencies | grep FAILED | grep -v "project :"

Explanation:

• :app:dependencies simply lists all the projects dependencies since app is the main application module,
• grep FAILED filters the output so that only the unresolvable dependencies are printed,
• grep -v "project :" filters out the unnecessary module dependencies in a multi-project build which could also be reported as FAILED.

You will probably see some duplicated entries in the console output, so you may want to try getting rid of them with some additional commands etc., but it was good enough for me.

The output may look like this (first 10 lines):

    |    +--- com.linkedin.dexmaker:dexmaker:2.21.0 FAILED
|    +--- com.google.android:flexbox:1.0.0 FAILED
     +--- com.android.volley:volley:1.1.1 FAILED
|    |    +--- com.linkedin.dexmaker:dexmaker:2.21.0 FAILED
|    +--- com.google.android:flexbox:1.0.0 FAILED
|    +--- com.android.volley:volley:1.1.1 FAILED
     |    +--- com.linkedin.dexmaker:dexmaker:2.21.0 FAILED
|    |    +--- com.linkedin.dexmaker:dexmaker:2.21.0 FAILED
|    +--- com.amitshekhar.android:debug-db:1.0.6 FAILED
|    |    |    +--- com.google.android:flexbox:1.0.0 FAILED

How to find your dependencies in other Maven repositories

Now, knowing which dependencies you miss, you can use a service like MvnRepository to see if there are other Maven repositories hosting them. For example, in case of this dependency:

|    +--- com.linkedin.dexmaker:dexmaker:2.21.0 FAILED

you will see on this page that:

• this particular version, i.e. 2.21.0, is hosted only on JCenter;
• a newer version, 2.28.1, is hosted on Maven Central.

In this case, you can't use any other Maven repository to get the current dependency version, but you can try to update it.

By the way, Dexmaker maintainers stated they won't migrate the older version here.

How to enforce a transitive dependency version

Since, in most cases, Dexmaker is not going to be your direct dependency, but a transitive one (in my case it is used by a popular Kotlin mocking library, MockK), you won't be able to simply change the version somewhere in your Gradle config file.

To update a transitive dependency version, you can use the constrains like:

dependencies {
    constraints {
        implementation("com.linkedin.dexmaker:dexmaker:2.28.1") {
            because("The default version used by MockK 1.9.3 is hosted on JCenter only")
        }
    }
}

or you can use a resolution strategy, e.g.:

allprojects {
    configurations.all {
        resolutionStrategy {
            force("com.linkedin.dexmaker:dexmaker:2.28.1")
        }
    }
}

Dependencies I couldn't find elsewhere

Unfortunately, the story doesn't end here. Updating the dependencies may lead to further issues. Some of them may be mutually incompatible while others will require updating some parts of the code in your project which can take a lot of effort. Moreover, it may turn out the library author doesn't maintain it anymore or simply didn't have enough time to upload it to a different Maven repository like Maven Central (which, by the way, is said to be very strict in terms of validation).

In all these cases you may need to keep the current dependency version somehow. I will explain how to do it in the next paragraphs so keep reading 🙂.

I decided to keep the following dependencies which I couldn't find anywhere else:

• com.datadoghq:dd-sdk-android:1.5.1 (direct)
• com.savvi.datepicker:rangepicker:1.3.0 (direct)
• com.google.android:flexbox:1.0.0 (transitive)
• com.android.volley:volley:1.1.1 (transitive)
• com.linkedin.dexmaker:dexmaker:2.21.0 (transitive)
• com.sunmi:printerlibrary:1.0.13 (direct)

Finding the cached dependencies in Gradle cache

Thankfully, Gradle caches the dependencies locally, so I was able to find all of them easily. By default, you should check your user's home directory: ~/.gradle. Here you can find a full explanation of the directories' layout.

You can run a command like this to find the cached dependency files:

find ~/.gradle/caches/modules-2/files 2.1/com.linkedin.dexmaker

and it will print an output like:

/Users/azabost/.gradle/caches/modules-2/files-2.1/com.linkedin.dexmaker
/Users/azabost/.gradle/caches/modules-2/files-2.1/com.linkedin.dexmaker/dexmaker
/Users/azabost/.gradle/caches/modules-2/files-2.1/com.linkedin.dexmaker/dexmaker/2.21.0
/Users/azabost/.gradle/caches/modules-2/files-2.1/com.linkedin.dexmaker/dexmaker/2.21.0/bdfd84d002e265ab7cf7f54a71a17717f831a57d
/Users/azabost/.gradle/caches/modules-2/files-2.1/com.linkedin.dexmaker/dexmaker/2.21.0/bdfd84d002e265ab7cf7f54a71a17717f831a57d/dexmaker-2.21.0-javadoc.jar
/Users/azabost/.gradle/caches/modules-2/files-2.1/com.linkedin.dexmaker/dexmaker/2.21.0/423b7b6e4d772e274ba03646284b0cea83faca56
/Users/azabost/.gradle/caches/modules-2/files-2.1/com.linkedin.dexmaker/dexmaker/2.21.0/423b7b6e4d772e274ba03646284b0cea83faca56/dexmaker-2.21.0.pom
/Users/azabost/.gradle/caches/modules-2/files-2.1/com.linkedin.dexmaker/dexmaker/2.21.0/680f2dbbb51f2892a4fdbbd9269d628e0b3270b3
/Users/azabost/.gradle/caches/modules-2/files-2.1/com.linkedin.dexmaker/dexmaker/2.21.0/680f2dbbb51f2892a4fdbbd9269d628e0b3270b3/dexmaker-2.21.0.jar
/Users/azabost/.gradle/caches/modules-2/files-2.1/com.linkedin.dexmaker/dexmaker/2.21.0/2e6b7df791ab40f340dfd2cb41acd62bb057af82
/Users/azabost/.gradle/caches/modules-2/files-2.1/com.linkedin.dexmaker/dexmaker/2.21.0/2e6b7df791ab40f340dfd2cb41acd62bb057af82/dexmaker-2.21.0-sources.jar

Now you need just a few additional steps to preserve these precious files in your VCS for as long as you need and share them with your teammates.

Setting up a local Maven repository

You can use any directory you want as a Maven repository using a Gradle snippet like this one:

repositories {
    maven {
        url = uri("${rootProject.projectDir}/libs")
    }
}

(You may want to put it inside allProjects { ... } block.)

As a result, the libs directory in the root project's directory will be searched for the dependencies just like all the other Maven repositories. Of course, you can name that directory as you wish.

The chosen directory must be prepared according to the Maven repository layout. To be honest, I'm not sure which documentation on this topic is the official one, but I found this one and I examined the local ~/.m2/repository directory to figure it out.

For Dexmaker I created the following directory:

libs/com/linkedin/dexmaker/dexmaker/2.21.0

As you can see, I mapped my Gradle cache structure into Maven repository layout like this:

Then I copied all the files from Gradle cache to libs using the following command:

find ~/.gradle/caches/modules-2/files-2.1/com.linkedin.dexmaker/dexmaker/2.21.0 -type f -exec cp -v {} libs/com/linkedin/dexmaker/dexmaker/2.21.0 \;

which printed this output:

/Users/azabost/.gradle/caches/modules-2/files-2.1/com.linkedin.dexmaker/dexmaker/2.21.0/bdfd84d002e265ab7cf7f54a71a17717f831a57d/dexmaker-2.21.0-javadoc.jar -> libs/com/linkedin/dexmaker/dexmaker/2.21.0/dexmaker-2.21.0-javadoc.jar
/Users/azabost/.gradle/caches/modules-2/files-2.1/com.linkedin.dexmaker/dexmaker/2.21.0/423b7b6e4d772e274ba03646284b0cea83faca56/dexmaker-2.21.0.pom -> libs/com/linkedin/dexmaker/dexmaker/2.21.0/dexmaker-2.21.0.pom
/Users/azabost/.gradle/caches/modules-2/files-2.1/com.linkedin.dexmaker/dexmaker/2.21.0/680f2dbbb51f2892a4fdbbd9269d628e0b3270b3/dexmaker-2.21.0.jar -> libs/com/linkedin/dexmaker/dexmaker/2.21.0/dexmaker-2.21.0.jar
/Users/azabost/.gradle/caches/modules-2/files-2.1/com.linkedin.dexmaker/dexmaker/2.21.0/2e6b7df791ab40f340dfd2cb41acd62bb057af82/dexmaker-2.21.0-sources.jar -> libs/com/linkedin/dexmaker/dexmaker/2.21.0/dexmaker-2.21.0-sources.jar

and that's how Dexmaker 2.21.0 became a part of the Git repository. After repeating this process for all the other missing dependencies, I was able to build the project successfully again 🎉

By Andrzej Zabost, Senior Android Developer @ Bright Inventions

Featured image by Luroka from Pixabay