Chapter 20. The Build Lifecycle

A Gradle build has three distinct phases.

Beside the build script files, Gradle defines a settings file. The settings file is determined by Gradle via a naming convention. The default name for this file is settings.gradle. Later in this chapter we explain how Gradle looks for a settings file.

The settings file is executed during the initialization phase. A multiproject build must have a settings.gradle file in the root project of the multiproject hierarchy. It is required because the settings file defines which projects are taking part in the multi-project build (see Chapter 24, Multi-project Builds). For a single-project build, a settings file is optional. Besides defining the included projects, you might need it to add libraries to your build script classpath (see Chapter 41, Organizing Build Logic). Let's first do some introspection with a single project build:

println 'This is executed during the initialization phase.'

println 'This is executed during the configuration phase.'

task configured {
    println 'This is also executed during the configuration phase.'
}

task test << {
    println 'This is executed during the execution phase.'
}

task testBoth {
    doFirst {
      println 'This is executed first during the execution phase.'
    }
    doLast {
      println 'This is executed last during the execution phase.'
    }
    println 'This is executed during the configuration phase as well.'
}

> gradle test testBoth
This is executed during the initialization phase.
This is executed during the configuration phase.
This is also executed during the configuration phase.
This is executed during the configuration phase as well.
:test
This is executed during the execution phase.
:testBoth
This is executed first during the execution phase.
This is executed last during the execution phase.

BUILD SUCCESSFUL

Total time: 1 secs

For a build script, the property access and method calls are delegated to a project object. Similarly property access and method calls within the settings file is delegated to a settings object. Look at the Settings class in the API documentation for more information.

A multi-project build is a build where you build more than one project during a single execution of Gradle. You have to declare the projects taking part in the multiproject build in the settings file. There is much more to say about multi-project builds in the chapter dedicated to this topic (see Chapter 24, Multi-project Builds).

include 'project1', 'project2:child', 'project3:child1'

includeFlat 'project3', 'project4'

println rootProject.name
println project(':projectA').name

rootProject.name = 'main'
project(':projectA').projectDir = new File(settingsDir, '../my-project-a')
project(':projectA').buildFileName = 'projectA.gradle'

How does Gradle know whether to do a single or multiproject build? If you trigger a multiproject build from a directory with a settings file, things are easy. But Gradle also allows you to execute the build from within any subproject taking part in the build. ^[9] If you execute Gradle from within a project with no settings.gradle file, Gradle looks for a settings.gradle file in the following way:

What is the purpose of this behavior? Gradle needs to determine whether the project you are in is a subproject of a multiproject build or not. Of course, if it is a subproject, only the subproject and its dependent projects are built, but Gradle needs to create the build configuration for the whole multiproject build (see Chapter 24, Multi-project Builds). You can use the -u command line option to tell Gradle not to look in the parent hierarchy for a settings.gradle file. The current project is then always built as a single project build. If the current project contains a settings.gradle file, the -u option has no meaning. Such a build is always executed as:

The automatic search for a settings.gradle file only works for multi-project builds with a physical hierarchical or flat layout. For a flat layout you must additionally follow the naming convention described above (“master”). Gradle supports arbitrary physical layouts for a multiproject build, but for such arbitrary layouts you need to execute the build from the directory where the settings file is located. For information on how to run partial builds from the root see Section 24.4, “Running tasks by their absolute path”.

Gradle creates a Project object for every project taking part in the build. For a multi-project build these are the projects specified in the Settings object (plus the root project). Each project object has by default a name equal to the name of its top level directory, and every project except the root project has a parent project. Any project may have child projects.

For a single project build, the workflow of the after initialization phases are pretty simple. The build script is executed against the project object that was created during the initialization phase. Then Gradle looks for tasks with names equal to those passed as command line arguments. If these task names exist, they are executed as a separate build in the order you have passed them. The configuration and execution for multi-project builds is discussed in Chapter 24, Multi-project Builds.

Your build script can receive notifications as the build progresses through its lifecycle. These notifications generally take two forms: You can either implement a particular listener interface, or you can provide a closure to execute when the notification is fired. The examples below use closures. For details on how to use the listener interfaces, refer to the API documentation.

allprojects {
    afterEvaluate { project ->
        if (project.hasTests) {
            println "Adding test task to $project"
            project.task('test') << {
                println "Running tests for $project"
            }
        }
    }
}

hasTests = true

> gradle -q test
Adding test task to project ':projectA'
Running tests for project ':projectA'

gradle.afterProject {project, projectState ->
    if (projectState.failure) {
        println "Evaluation of $project FAILED"
    } else {
        println "Evaluation of $project succeeded"
    }
}

> gradle -q test
Evaluation of root project 'buildProjectEvaluateEvents' succeeded
Evaluation of project ':projectA' succeeded
Evaluation of project ':projectB' FAILED

tasks.whenTaskAdded { task ->
    task.ext.srcDir = 'src/main/java'
}

task a

println "source dir is $a.srcDir"

> gradle -q a
source dir is src/main/java

task ok

task broken(dependsOn: ok) << {
    throw new RuntimeException('broken')
}

gradle.taskGraph.beforeTask { Task task ->
    println "executing $task ..."
}

gradle.taskGraph.afterTask { Task task, TaskState state ->
    if (state.failure) {
        println "FAILED"
    }
    else {
        println "done"
    }
}

> gradle -q broken
executing task ':ok' ...
done
executing task ':broken' ...
FAILED