Extending Gradle
Internal
Overview
The simplest way to extend Gradle is to write a custom task, which can be declared in-line in the project's build.gradle or in a script plugin, in the projects's buildSrc directory or in can be external to project and provided back to the Gradle runtime as a JAR. More complex behavior that goes beyond the capabilities of a custom task can be implemented as a custom object plugin, which has the same choice in terms of where the code lives.
Extensions Code Location
In-line in build.gradle
Both custom tasks (simple or enhanced) and binary plugins can be fully declared in-line in build.gradle. While declaring simple custom tasks in-line is acceptable, provided that the tasks are not intended for reuse and sharing among other projects, declaring enhanced tasks or even full binary plugin in-line is, albeit possible, not recommended.
Examples:
- Custom simple task declared in-line in build.gradle
- Custom ehanced Java task declared in-line in build.gradle
In-line in a script plugin
A script plugin is a regular Gradle build script that can be imported into another build script. Both custom tasks and "binary" plugin code can be declared in-line in a script plugin.
Example of a custom simple task declared in-line in a script plugin.
In the Project's buildSrc Directory
This is a good choice while developing a custom task or a plugin, because it gives a quick feedback loop and allows for in-line debugging. The 'buildSrc' directory is itself a Gradle project and has a standard Maven layout. It could have a build.gradle, but it seems that for simple Java compilation that does not require external dependencies works without it. buildSrc/build.gradle proves useful when the custom code task being developed requires external dependencies. In that case, the dependencies must be declared in buildSrc/build.gradle.
.
├── build.gradle
├── buildSrc
│ ├── build.gradle
│ └── src
│ └── main
│ └── java
│ └── playground
│ └── gradle
│ └── CustomEnhancedTask.java
└ ...
Example of an enhanced task developed in buildSrc.
External to Project
Extension code can live in separate standalone projects that publish JARs. Those JARs can be declared as dependencies by a Gradle project that can then use the custom task or the binary plugin externally developed.