/ Java

Gradle Offline Build

The Problem

In a recent project, I have to do Gradle build on a CI server in a very constrained environment. The constraints are:

  • NO Internet connection
  • NO Gradle installed
  • NO local Maven repo

The obvious problem that these constraints cause is that the project can't build because:

  • Gradle is not installed
  • Can't get dependencies

The Solution

This solution will achieve the following:

  1. Use Gradle to build
  2. Use Gradle to manage dependencies

Let's solve the problem step by step.

Gradle Wrapper

Put simply, Gradle Wrapper is the way to let you run Gradle without installing it. It's done by running a shell/batch script to download Gradle binary (More on Gradle Wrapper here).
But the CI server has no Internet connection, how to download Gradle binary? Simply modify distributionUrl in gradle-wrapper.properties to a local path, e.g.

# Sample gradle-wrapper.properties
# Other properties omitted
distributionUrl=gradle-2.4-bin.zip

And put gradle-2.4-bin.zip (You can get all Gradle distributions from here) in ${projectDir}/gradle/wrapper. You should add this file in source control.

From now on, you can build using Gradle without Gradle installed, e.g. (assuming on Mac or Linux) ./gradlew clean build.

Local Dependencies

To let Gradle manage dependencies and smartly load them from the right place, we need a way to store the dependencies and load them conditionally.

In build.gradle,

ext.libs = "$projectDir/libs"
ext.compileLib = "${libs}/compile"
ext.runtimeLib = "${libs}/runtime"
ext.testCompileLib = "${libs}/testCompile"
ext.testRuntimeLib = "${libs}/testRuntime"

dependencies {
    if (gradle.startParameter.isOffline()) {
        compile fileTree(dir: compileLib)
        runtime fileTree(dir: runtimeLib)
        testCompile fileTree(dir: testCompileLib)
        testRuntime fileTree(dir: testRuntimeLib)
    } else {
        compile 'com.google.guava:guava:18.0'
        testCompile group: 'junit', name: 'junit', version: '4.11'
    }
}

By doing this, if Gradle is running in offline mode, it will load dependencies from local subdirectories in the project. Otherwise, it will try to get them from Gradle home or download from the Internet. I choose the parameter offline because I think it's the best parameter that fits the purpose. Of course, you can use other parameter.

How to store dependent jars in the local subdirectories? A simple copyToLibs task would do the job.

task deleteLibs(type: Delete) {
    delete 'libs/compile'
    delete 'libs/runtime'
    delete 'libs/testCompile'
    delete 'libs/testRuntime'
}

task copyToLibs(dependsOn: 'deleteLibs') << {
    ['compile', 'runtime', 'testCompile', 'testRuntime'].each { scope ->
        copy {
            from configurations.getByName(scope).files
            into "${libs}/${scope}"
        }
    }
}

To make this whole thing work, when developing on your local machine, before pushing to Git server, you should run copyToLibs to make sure that the required dependencies are copied to the local subdirectories and add those dependencies to Git.

On the CI server, run ./gradlew --offline clean build. Your tasks may vary but make sure that --offline is passed in because that's the way to tell Gradle to find dependencies from local dirs, instead of Gradle home or the Internet.

Summary

By using Gradle Wrapper and storing dependencies in local directories of the project, we can still build and manage dependencies using Gradle. I think this is a simple and elegant solution. If you know a better one, leave a comment or drop me an email (me [at] this domain).

A demo app is available here.

Gradle Offline Build
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