Gradle Variables and Properties
External
Internal
Overview
System Properties
A system property in a Gradle runtime context is a regular JVM system property that has no special signification to Gradle, with the exception of "gradle.wrapperUser", "gradle.wrapperPassword" and "gradle.user.home".
System properties can be declared in command line with -D. The -D option of the gradle command has the same effect as the -D option of the java command.
-D=<propName>=<propValue>
System properties can also be declared in gradle.properties files with a special syntax:
systemProp.<propName>=<propValue>
The "systemProp." system properties set in a multi-project build gradle.properties files in any project except root will be ignored. Only the root project's gradle.properties will be checked for properties that begin with "systemProp." prefix.
When the same system property is declared in multiple places, the effective value is subject to the property declaration precedence rules.
There are no special syntactic facilities to access system properties from build scripts, unlike project properties that have a special simplified syntax for access.
task printProp {
doLast {
println System.properties['mySystemPropA']
println System.getProperty('mySystemPropA')
}
}
All other equivalent JDK API is available:
System.getProperty('myPropertyName', 'DefaultValue')
If we known that the system property has boolean semantics, we can use:
Boolean.getBoolean(...)
Note that an attempt to access a non-existent system property from a build script won't trigger a build error, it will simply return null.
Note that:
gradle properties
does not show system properties declared with -D=... on command line, but does show system properties declared with "systemProp." in gradle.properties files.
Property Declaration Precedence Rules
Gradle Properties
These are properties that can be used to configure aspects of a Gradle build run, regardless of the specific of the project being built. They can be seen as Gradle runtime configuration options, and can be used to configure the following aspects:
- Build artifact caching: org.gradle.caching, org.gradle.caching.debug.
- Configuration on demand: org.gradle.configureondemand.
- Gradle runtime configuration, such as console output coloring and verbosity, running in debug mode, JVM arguments, logging level, running in parallel mode, etc.
- Whether Gradle Daemon runs or not and its operational parameters.
The Gradle properties can be declared on command line with -D=... or in gradle.properties.
Project Properties
A Gradle project property is a key value pair that can be accessed directly from build scripts without any qualifier. Project properties is a mechanism designed for easy access. It can be considered logically attached directly to the project.
A project property can be accessed without any qualifier:
task printProp {
doLast {
println myProjectProp
}
}
An important characteristic of project properties is that an attempt to access a project property that was not explicitly defined using one of the means described below will trigger a build error.
task printProp {
doLast {
println thisProjectPropertyWasNotDefined
}
}
FAILURE: Build failed with an exception. * Where: Build file '/Users/ovidiu/playground/gradle/concepts/build.gradle' line: 11 * What went wrong: Execution failed for task ':printProps'. > Could not get unknown property 'thisProjectPropertyWasNotDefined' for task ':printProps' of type org.gradle.api.DefaultTask.
Accessing Properties
The effective value of the properties can be displayed with:
gradle properties
Accessing Gradle Properties
Overview
NEEDS REFACTORING.
Configuration scripts can declare variables during the initialization and configuration phases, and the values of those variables can be accessed and updated during the execution phase and used to drive build logic. There are two types of variables that can be declared: local variables and extra properties.
Properties can be displayed with:
gradle properties
The command displays project properties, and the properties added by various plugins.
Gradle Properties
Also see:
System Properties
Local Variables
Local variables, which are a feature of the underlying Groovy language, are declared with the "def" keyword. They are only visible in the scope where they have been declared. The scope include all closures declared in scope.
def myVariable = "something"
...
println myVariable
Extra Properties
An extra property is a property that can be declared on most model object instances available to the closure being executed. In case of a settings script, the available model objects are Settings, Gradle, ProjectDescriptor, etc., but of those ProjectDescriptor does not allow defining extra properties, and Settings, even if allows defining extra properties, cannot be easily accessed at configuration and execution phase, so the best candidate for defining extra properties is Gradle. For build scripts, extra properties can be defined on any available object model instances. They can be declared with a special syntax described below. Once the properties have been added, they can be read and set like predefined properties. Extra properties can be accessed from anywhere their owning object can be accessed, giving them a wider scope than local variables. Extra properties on a project are visible from its sub-projects.
By requiring special syntax for adding a property, Gradle can fail fast when an attempt is made to set a predefined or extra property but the property is misspelled or does not exist.
Declaring and Using Extra Properties
The extra properties are declared using the "ext" DSL keyword, applied to the model object we intend to declare extra properties for. However, "ext" is not necessary to access the property once declared, as shown in the examples below:
Initialization Phase
The property is defined in settings.gradle:
...
gradle.ext.color = "blue"
...
The property can be accessed anywhere in a build or settings script:
println "gradle is $gradle.color"
Extra Properties and Multi-Project Builds
The extra properties are not available and throw an execution error if they are accessed before are defined. That is why a multi-project build that declares extra properties in sub-projects' build.gradle and attempts to use them in the root project build.gradle will fail at the configuration phase:
BUILD FAILED in 3s ... * Where: Build file '.../root-project/build.gradle' line: 17 * What went wrong: A problem occurred evaluating root project 'root-project'. > Could not get unknown property 'blah' for project ':sub-project-A' of type org.gradle.api.Project.
The error occurs even "blah" was declared in sub-project-A's build.gradle, because the build file was not evaluated at the time the root project file is executed. If we log build.gradle evaluation, we get something like:
exiting root project build.gradle .... entering sub-project-A build.gradle .... exiting sub-project-A build.gradle ....
which shows that the sub-project build script is executed after the root project build script is executed.
At Configuration Phase
The property can be declared in a build script as follows:
project.ext.isApi = true
The property can be accessed anywhere in a build script:
println isApi
Declaring multiple extra properties in a closure:
...
ext {
log4jVersion = "2.1.7"
emailNotification = "build@example.com"
}
...
Auto-Delegation
Properties not defined in the build script are auto-delegating to the Project instance. For example:
name
and
project.name
are equivalent. Normally, using "name" is sufficient. In case you define a property or a method which has the same name as a member of the Project object, you will need to use the project property.
Predefined Properties
Project Coordinates
name
A String containing the name of the project directory. It automatically becomes the project's name coordinate. See Gradle Project Coordinates.
group
See Gradle Project Coordinates - Group.
version
See Gradle Project Coordinates - Version.
parent
Other Properties
project
The Project instance.
projectDir
The File instance corresponding to the directory containing the build script.
path
A String containing the absolute path of the project. The path of the root project is ":"
description
A String containing the description for the project.
displayName
buildDir
A File representing <projectDir>/build.
buildFile
rootDir
rootProject
rootProject.name
state
status
Plugin Properties
Plugins add specific properties. For a list of properties added by various plugins, consult the plugin pages.