Gradle multi project, how to deal with different rootDirs

Question

My company is currently switching from Ant to Gradle for its Java projects, but I am stuck with a nice clean setup. Let's say I work for a company that builds websites for clients which generally use the same root libraries (core project), but have some specific code, which is put in the sub-project. Per client, we build a new sub-project, that depends on the core project. Number of clients will increase in the future.

Currently we have three projects:

• A core project. This should run individually, as we want to be able to do the unit testing seperately for this.
• Two sub-projects that depend on the core project, but have some own projects that are specific to the project.

I was sucessful in converting the whole ant build into a gradle build for the core project. My idea is to have all functionality and project structure in the core, and only the extra for what is actually needed in the sub-projects.

Here is a short sample of our folder structure:

-- core
    - build.gradle
    - settings.gradle
    -- repository (our external jars used)
    -- Implementation
      -- source_code
        -- all the core project folders
      -- Projects
        -- Client A
          - build.gradle
          - settings.gradle
          -- more project specific folders
        -- Client B
          - build.gradle
          - settings.gradle
          -- more project specific folders

I use the $rootDir variable a lot. A fraction of the core's settings.gradle looks as such:

project(':CoreProjectA').projectDir = new File(rootDir, 'Implementation/Source_code/Core/coreA')
project(':CoreProjectB').projectDir = new File(rootDir, 'Implementation/Source_code/Core/CoreB')

But with many more. Also, in the core build.gradle, I refer to our repository as such:

repositories {
   //All sub-projects will now refer to the same 'libs' directory
    flatDir {
        dirs "$rootDir/repository/lib/jaxb"
        //many more dirs here
    }
}

Now this all works great when I do a gradle build from the core project. I was planning to put the next piece of code in every client's subproject build.gradle:

apply from: '../../../build.gradle'

When I run a gradle build from Client A folder, my rootDir obviously has changed, and now, all my paths cannot be found anywhere.

Is there any way to set this up in a nice clean way? So that every future sub project added can always use the same structure? Or will I have to give each sub-project its own build.gradle and settings.gradle entirely?

I know the last option could work, but it is a lot of overhead, and just doesn't seem nice and clean to me at all..

Thanks in advance!

Answer 1

I want to thank Nikita and especially lukegv for his detailed answer, but I went with a different approach ultimately.

I didn't want to have one main gradle build and extend it each time we have a new project. Also, I wanted to keep it simple and logical for my colleagues if they want to create a build for one of the projects.

Therefor, I kept the structure I had as described above. In the root gradle.settings but changed the

project(':CoreProjectA').projectDir = new File(rootDir, 'Implementation/Source_code/Core/coreA')
project(':CoreProjectB').projectDir = new File(rootDir, 'Implementation/Source_code/Core/CoreB')

into:

project(':CoreProjectA').projectDir = new File(customRootDir, 'Implementation/Source_code/Core/coreA')
project(':CoreProjectB').projectDir = new File(customRootDir, 'Implementation/Source_code/Core/CoreB')

In each project I have a properties.gradle with the customRootDir filled in (relatively to the projects directory).

It all works like a charm. I can go into any project folder and produce builds, while using the functionality of the root's build.gradle.

Answer 2

I recently worked on a similar configuration, so let me explain me how I build the Gradle infrastructure. Since you mentioned a lot of requirements, I hope that I'll miss any of them and you can apply my scheme to your problem.

General

We actually use build systems (like Gradle) to let them take care of any dependencies (projects, modules, tasks). So why should we define a depedency in something like a filesystem hierarchy, if we can simply define it in Gradle?

I would avoid using paths as much as possible (convention over configuration) and try to stick to Gradle projects for both the build scripts and the dependencies.

Also, if you define dependencies in your core gradle.build, you should just call this gradle file, even if you only want to build a subproject. Your apply from: '../../../build.gradle' destroys the whole Gradle logic. Instead you should use something like gradle :sub1:build to only build the first subproject.

First approach (with core as root project)

Filesystem structure:

core/
    build.gradle
    settings.gradle
    src/
        ...
    sub1/
        src/
            ...
        build.gradle [optional]
    sub2/
        src/
            ...
        build.gradle [optional]

Core settings.gradle:

include 'sub1'
include 'sub2'

Core build.gradle:

allprojects {
     apply plugin: 'java'

     repositories {
         // define repos for all projects
     }
}

subprojects {
     dependencies {
         // let subprojects depend on core
         compile rootProject
     }
}

project(':sub1') {
     // define anything you want (e.g. dependencies) just for this subproject
     // alternative: use build.gradle in subproject folder
}

Second approach (all projects independent)

Filesystem structure:

core/
    src/
        ...
    build.gradle [optional]
sub1/
    src/
        ...
    build.gradle [optional]
sub2/
    src/
        ...
    build.gradle [optional]
build.gradle
settings.gradle

Root settings.gradle:

include 'core'
include 'sub1'
include 'sub2'

Root 'build.gradle'

subprojects {
    apply plugin: 'java'

    repositories {
        // define repos for all projects
    }
}

configure(subprojects.findAll {it.name != 'core'}) {
    dependencies {
        // Add dependency on core for sub1 and sub2
        compile project(':core')
    }
}

project(':sub1') {
     // define anything you want (e.g. dependencies) just for this subproject
     // alternative: use build.gradle in subproject folder
}

This approach provides great flexibility, since every dependency logic is handled by Gradle and you'll never have to copy anything to another position. Simply change the dependency and you are fine.

Sources

Gradle Tutorial on Multi-project Builds

Question in Gradle Forum

Answer 3

It looks like you have extra settings.gradle inside subprojects. That makes Gradle think the sub-project is a standalone one. If you remove settings.gradle from subprojects, Gradle will look for it up the filesystem hierarchy, will find one in core project, will create correct multimodule project and all the paths should work properly.

So, just remove extra settings.gradle files and your build will work fine. Having build.gradle in subprojects is perfectly fine.