52.1. Inherited properties and methods
Any method or property defined in a project build script is also visible to all the sub-projects. You can use this to define common configurations, and to extract build logic into methods which can be reused by the sub-projects.
Example 52.1. Using inherited properties and methods
build.gradle
srcDirName = 'src/java'
def getSrcDir(project) {
return project.file(srcDirName)
}
child/build.gradle
task show << {
// Use inherited property
println 'srcDirName: ' + srcDirName
// Use inherited method
File srcDir = getSrcDir(project)
println 'srcDir: ' + rootProject.relativePath(srcDir)
}
Output of gradle -q show
> gradle -q show srcDirName: src/java srcDir: child/src/java
52.2. Injected configuration
You can use the configuration injection technique discussed in Section 49.1, “Cross proje configuration” and Section 49.2, “Subproject configuration”to inject properties and methods into various projects. This is generally a better option than inheritance, for a number of reasons: The injection is explicit in the build script, You can inject different logic into different projects, And you can inject any kind of configuration such as repositories, plug-ins, tasks, and so on. The following sample shows how this works.
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Example 52.2. Using injected properties and methods
build.gradle
subprojects {
//Inject a property and method srcDirName = 'src/java'
srcDir = { file(srcDirName) }
//Inject a task
task show << {
println 'project: ' + project.path println 'srcDirName: ' + srcDirName File srcDir = srcDir()
println 'srcDir: ' + rootProject.relativePath(srcDir)
}
}
// Inject special case configuration into a particular project project(':child2') {
srcDirName = "$srcDirName/legacy"
}
child1/build.gradle
// Use injected property and method. Here, we override the injected value srcDirName = 'java'
def dir = srcDir()
Output of gradle -q show
> gradle -q show project: :child1 srcDirName: java srcDir: child1/java project: :child2
srcDirName: src/java/legacy srcDir: child2/src/java/legacy
52.3. Build sources in the buildSrc project
When you run Gradle, it checks for the existence of a directory called buildSrc. Gradle then automatically compiles and tests this code and puts it in the classpath of your build script. You don't need to provide any further instruction. This can be a good place to add your custom task and plugins.
For multi-project builds there can be only one buildSrc directory, which has to be in the root project directory.
Listed below is the default build script that Gradle applies to the buildSrc project:
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Figure 52.1. Default buildSrc build script
apply plugin: 'groovy' dependencies {
compile gradleApi() groovy localGroovy()
}
This means that you can just put you build source code in this directory and stick to the layout convention for a Java/Groovy project (see Table 23.4, “Java plugin - default project layou)t”.
If you need more flexibility, you can provide your own build.gradle. Gradle applies the default build script regardless of whether there is one specified. This means you only need to declare the extra things you need. Below is an example. Notice that this example does not need to declare a dependency on the Gradle API, as this is done by the default build script:
Example 52.3. Custom buildSrc build script
buildSrc/build.gradle
repositories { mavenCentral()
}
dependencies {
testCompile group: 'junit', name: 'junit', version: '4.8.2'
}
The buildSrc project can be a multi-project build. This works like any other regular Gradle multi-project build. However, you need to make all of the projects that you wish be on the classpath of the actual build runtime dependencies of the root project in buildSrc. You can do this by adding this to the configuration of each project you wish to export:
Example 52.4. Adding subprojects to the root buildSrc project
buildSrc/build.gradle
rootProject.dependencies { runtime project(path)
}
Note: The code for this example can be found at samples/multiProjectBuildSrc which
is in both the binary and source distributions of Gradle.
52.4. Running another Gradle build from a build
You can use the GradleBuild task. You can use either of the dir or buildFile properties to specify which build to execute, and the tasks property to specify which tasks to execute.
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Example 52.5. Running another build from a build
build.gradle
task build(type: GradleBuild) { buildFile = 'other.gradle' tasks = ['hello']
}
other.gradle
task hello << {
println "hello from the other build."
}
Output of gradle -q build
> gradle -q build
hello from the other build.
52.5. External dependencies for the build script
If your build script needs to use external libraries, you can add them to the script's classpath in th build script itself. You do this using the buildscript() method, passing in a closure which declares the build script classpath.
Example 52.6. Declaring external dependencies for the build script
build.gradle
buildscript { repositories {
mavenCentral()
}
dependencies {
classpath group: 'commons-codec', name: 'commons-codec', version: '1.2
}
}
The closure passed to the buildscript() method configures a ScriptHandler instance. You declare the build script classpath by adding dependencies to the classpath configuration. This is the same way you declare, for example, the Java compilation classpath. You can use any of the dependency types described in Section 43.4, “How to declare your dependencies”,except project dependencies.
Having declared the build script classpath, you can use the classes in your build script as you would any other classes on the classpath. The following example adds to the previous example, and uses classes from the build script classpath.
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