Gradle builds a script file for handling two things; one is projects and another one is tasks. Every Gradle build represents one or more projects. A project represents a library JAR or a web application or it might represent a ZIP that assembled from the JARs produced by other projects. In simple words, a project is made up of different tasks. A task means a piece of work which a build performs. A task might be compiling some classes, creating a JAR, generating Javadoc, or publishing some archives to a repository.
Gradle uses Groovy language for writing scripts.
Writing Build Script
Gradle provides a Domain Specific Language (DSL), for describing builds. This uses the Groovy language to make it easier to describe a build. Each build script of Gradle is encoded using UTF-8, saved offline and named as build.gradle.
build.gradle
We are describing about tasks and projects by using a Groovy script. You can run a Gradle build using the Gradle command. This command looks for a file called build.gradle. Take a look at the following example which represents a small script that prints howcodex. Copy and save the following script into a file named build.gradle. This build script defines a task name hello, which is used to print howcodex string.
task hello {
doLast {
println 'howcodex'
}
}
Execute the following command in the command prompt. It executes the above script. You should execute this, where the build.gradle file is stored.
C:\> gradle –q hello
Output:
howcodex
If you think task works similar to ANT’s target, then that’s right − Gradle task is equivalent to ANT target.
You can simplify this hello task by specifying a shortcut (represents a symbol <<) to the doLast statement. If you add this shortcut to the above task hello it will look like the following script.
task hello << {
println 'howcodex'
}
As same above you can execute the above script using gradle –q hello command.
The Grade script mainly used two real Objects, one is Project Object and another one is Script Object.
Project Object − Each script describes about one or multiple projects. While in the execution this scripts configures the Project Object. You can call some methods and use property in your build script which are delegated to the Project Object.
Script Object − Gradle taken script code into classes which implements Script Interface and then executes. This means that of all the properties and methods declared by the script interface are available in your script.
The following table defines the list of standard project properties. All these properties are available in your build script.
Sr. No.
Name
Type
Default Value
1
project
Project
The Project instance
2
name
String
The name of the project directory.
3
path
String
The absolute path of the project.
4
description
String
A description for the project.
5
projectDir
File
The directory containing the build script.
6
buildDir
File
projectDir/build
7
group
Object
Unspecified
8
version
Object
Unspecified
9
ant
AntBuilder
An AntBuilder instance
Groovy Basics
Gradle build scripts use the full length Groovy API. As a startup, take a look at the following examples.
The following example explains about converting a string to upper case.
Copy and save the below given code into build.gradle file.
Execute the following command in the command prompt. It executes the above given script. You should execute this, where the build.gradle file is stored.
C:\> gradle –q upper
Output:
Original: TUTORIALS point
Upper case: TUTORIALS POINT
The following example explains about printing the value of an implicit parameter ($it) for 4 times.
Copy and save the following code into build.gradle file.
task count << {
4.times {
print "$it "
}
}
Execute the following command in the command prompt. It executes the above given script. You should execute this, where the build.gradle file is stored.
$ gradle –q count
Output:
0 1 2 3
Groovy language provides plenty of features in those some important features are discussed below.
Groovy JDK Methods
Groovy adds lots of useful methods to the standard Java classes. For example, Iterable API from JDK implements an each() method which iterates over the elements of the Iterable Interface.
Copy and save the following code into build.gradle file.
Execute the following command in the command prompt. It executes the above given script. You should execute this, where the build.gradle file stores.
C:\> gradle –q groovyJDK
Output:
M
a
r
c
Property Accessors
You can automatically accesses appropriate getter and setter methods of a particular property by specifying its reference.
The following snippet defines the syntaxes of getter and setter methods of a property buildDir.
// Using a getter method
println project.buildDir
println getProject().getBuildDir()
// Using a setter method
project.buildDir = 'target'
getProject().setBuildDir('target')
Optional Parentheses on Method Calls
Groovy contains a special feature in methods calling that is the parentheses are optional for method calling. This feature applies to Gradle scripting as well.
Take a look at the following syntax. That defines a method calling systemProperty of test object.
Gradle DSL uses closures in many places. Where the last parameter of a method is a closure, you can place the closure after the method call.
The following snippet defines the syntaxes Closures use as repositories() method parameters.
repositories {
println "in a closure"
}
repositories() {
println "in a closure"
}
repositories({ println "in a closure" })
Default Imports
Gradle automatically adds a set of import statements to the Gradle scripts. The following list shows you the default import packages to the Gradle script.
