Gradle Build Phases
A Gradle build typically goes through three main phases:
- Initialization Phase
- Configuration Phase
- Execution Phase
Initialization Phase
During the Initialization phase, Gradle determines which projects are going to take part in the build. For multi-project builds, it sets up the structure of the projects.
Example
In a single-project build, the Initialization phase is straightforward, with Gradle setting up the build for that single project. In a multi-project build, Gradle identifies and sets up all sub-projects.
Configuration Phase
In the Configuration phase, Gradle constructs and configures the project objects. This phase involves executing the build scripts for all projects to configure tasks.
Example
Consider the following build.gradle
file:
plugins {
id 'java'
}
repositories {
mavenCentral()
}
dependencies {
implementation 'org.apache.commons:commons-lang3:3.12.0'
}
During the Configuration phase, Gradle evaluates this script, setting up the repositories and dependencies for the project.
Execution Phase
In the Execution phase, Gradle executes the tasks that were selected for the build. This is the phase where the actual work is done, such as compiling code, running tests, and creating JAR files.
Example
If you run the gradle build
command, Gradle will execute the tasks associated with building the project, such as compileJava
, processResources
, classes
, jar
, and assemble
.
Common Gradle Tasks
Gradle tasks are the building blocks of a build script. Here are some commonly used tasks:
clean
The clean
task deletes the build directory, effectively cleaning the project.
gradle clean
build
The build
task is a lifecycle task that depends on other tasks to perform a full build of the project.
gradle build
assemble
The assemble
task compiles and packages the project but does not run tests.
gradle assemble
check
The check
task runs all verification tasks, such as tests.
gradle check
test
The test
task runs the unit tests.
gradle test
jar
The jar
task creates a JAR file containing the compiled classes.
gradle jar
Example: Custom Task
You can define custom tasks in your build.gradle
file. Here’s an example:
task hello {
doLast {
println 'Hello, Gradle!'
}
}
Run the custom task using:
gradle hello
Gradle Task Dependencies
Tasks in Gradle can have dependencies on other tasks. You can define these dependencies using the dependsOn
method.
Example
task compileJava {
doLast {
println 'Compiling Java source files...'
}
}
task compileResources {
doLast {
println 'Compiling resources...'
}
}
task build {
dependsOn compileJava, compileResources
doLast {
println 'Building the project...'
}
}
In this example, the build
task depends on compileJava
and compileResources
. Running gradle build
will first execute compileJava
and compileResources
before executing the build
task.
Gradle Plugins
Gradle plugins can add new tasks or enhance existing ones. Here are some useful plugins:
Java Plugin
The Java plugin adds tasks for compiling Java code, running tests, and packaging JAR files.
plugins {
id 'java'
}
Application Plugin
The Application plugin provides tasks for building and running Java applications.
plugins {
id 'application'
}
mainClassName = 'com.example.Main'
Example: Complete Build Script
Here’s a complete example of a build.gradle
file using several plugins and custom tasks:
plugins {
id 'java'
id 'application'
}
repositories {
mavenCentral()
}
dependencies {
implementation 'org.apache.commons:commons-lang3:3.12.0'
testImplementation 'org.junit.jupiter:junit-jupiter-api:5.10.0'
testRuntimeOnly 'org.junit.jupiter:junit-jupiter-engine:5.10.0'
}
application {
mainClassName = 'com.example.Main'
}
tasks.register('customTask') {
doLast {
println 'Executing custom task...'
}
}
build {
dependsOn 'customTask'
}
Conclusion
Understanding the Gradle build lifecycle and tasks is crucial for effectively managing and automating your build process. By leveraging Gradle’s powerful task system and plugins, you can streamline your build, test, and deployment workflows. This guide covered the key phases of the Gradle build lifecycle, common tasks, task dependencies, and the use of plugins with practical examples.
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