how-to-gradle-project-variations

Gradle example for generating dynamic subprojects with variations of the dependency graph.

Building

./gradlew war

Why

Suppose one needs to build a test web application for testing compatibility with an external tool such as a Java agent. It would be helpful to know that this test web application works with various versions of the web framework upon which it was built, so we want to repeat the project build with several versions of the web framework. The simplest way to do this is to introduce a Gradle property to represent the version of the web framework and use this property when defining the project's dependencies. Next, one can simply repeat the build with a shell script.

for version in 4.3.12 4.3.13 4.3.14; do
  ./gradlew war -PspringVersion=$version
done

Proposed Solution: dynamic subprojects

Use settings.gradle to dynamicaly generate subprojects for each of the variations of the web application we want to build.

| how-to-gradle-project-variations
├── app
├── build.gradle
├── settings.gradle
└── variations

The "app" directory contains the web application project

app/
└── src
    └── main
        └── java
            └── com
                └── johnathangilday
                    └── HelloWorldServlet.java

settings.gradle generates a subproject for each of the variations of the servlet-api dependency with which we want to build this project

// define versions of javax.servlet:servlet-api for which to generate variations
of the app
def variations = ['2.3', '2.4', '2.5']

def projects = variations.collect { "${rootProject.name}-${it}" }

// include the app subproject with the servlet definitions
include('app')
// include a subproject for each variation of the servlet-api
include(*projects)

/.gradlew projects shows us the dynamic subprojects generated in the "variations" directory

$ ./gradlew projects

> Task :projects

------------------------------------------------------------
Root project
------------------------------------------------------------

Root project 'how-to-gradle-project-variations'
+--- Project ':app'
+--- Project ':how-to-gradle-project-variations-2.3'
+--- Project ':how-to-gradle-project-variations-2.4'
\--- Project ':how-to-gradle-project-variations-2.5'