If we use Gradle in a multi-module project we can define project dependencies between modules. Gradle uses the information from the project dependencies to determine which tasks need to be run. For example if module B depends on module A and we want to build module B, Gradle will also build module A for us, because module B depends on it. But if we know for sure that module A is up to date and has not changed, we can also instruct Gradle to skip building module A, when we build module B.
Let's start with the following module structure, where each module depends on the module above it. So module services depends on common and module web depends on services:
. ├── common ├── services └── web
When we want to build the service module we go to the services directory and execute the build task and we get the following output:
$ gradle build :common:compileJava :common:processResources :common:classes :common:jar :services:compileJava :services:processResources :services:classes :services:jar :services:assemble :services:compileTestJava :services:processTestResources :services:testClasses :services:test :services:check :services:build BUILD SUCCESSFUL Total time: 8.013 secs
We see in the output that first the common module is build, because the services module depends on it. But if we work on this project and we know for sure the common module is up to date and has not changed since the last build (for example we didn't checkout new sources from version control or changed sources in the common module ourselves), then we can skip building the common module. We use the command line option -a or --no-rebuild to tell Gradle to skip project dependencies.
When we run the build task from the services directory using the command line option -a we get the following output:
$ gradle -a build :services:compileJava :services:processResources :services:classes :services:jar :services:assemble :services:compileTestJava :services:processTestResources :services:testClasses :services:test :services:check :services:build BUILD SUCCESSFUL Total time: 5.626 secs
This time only the services module is build, which also speeds up the build proces. Still this should only be used if we know ourselves the project dependencies are up to date.
Written with Gradle 2.2.1.
