第 2 部分：构建生命周期

了解 Gradle 构建生命周期以及每个阶段代表什么。

在本节中，您将：

了解构建生命周期
注册并配置两个任务
运行任务以查看操作中的阶段

步骤 0. 开始之前

您在第 1 部分中初始化了 Java 应用程序。

步骤 1.了解构建生命周期

Gradle 构建分为三个不同的阶段：

第 1 阶段 - 初始化: 在初始化阶段，Gradle 确定哪些项目将参与构建，并Project为每个项目创建一个实例。
第 2 阶段 - 配置: 在配置阶段，Project使用构建中所有项目的构建脚本来配置对象。 Gradle 确定要执行的任务集。
第三阶段 - 执行: 在执行阶段，Gradle 执行每个选定的任务。

当调用 Gradle 来执行任务时，生命周期就开始了。让我们看看它的实际效果。

步骤 2. 更新设置文件

将以下行添加到设置文件的顶部：

settings.gradle.kts

println("SETTINGS FILE: This is executed during the initialization phase")

settings.gradle

println('SETTINGS FILE: This is executed during the initialization phase')

步骤 3. 更新构建脚本

将以下行添加到构建脚本的底部：

app/build.gradle.kts

println("BUILD SCRIPT: This is executed during the configuration phase")

tasks.register("task1"){
    println("REGISTER TASK1: This is executed during the configuration phase")
}

tasks.register("task2"){
    println("REGISTER TASK2: This is executed during the configuration phase")
}

tasks.named("task1"){
    println("NAMED TASK1: This is executed during the configuration phase")
    doFirst {
        println("NAMED TASK1 - doFirst: This is executed during the execution phase")
    }
    doLast {
        println("NAMED TASK1 - doLast: This is executed during the execution phase")
    }
}

tasks.named("task2"){
    println("NAMED TASK2: This is executed during the configuration phase")
    doFirst {
        println("NAMED TASK2 - doFirst: This is executed during the execution phase")
    }
    doLast {
        println("NAMED TASK2 - doLast: This is executed during the execution phase")
    }
}

println("BUILD SCRIPT: This is executed during the configuration phase")

tasks.register("task1") {
    println("REGISTER TASK1: This is executed during the configuration phase")
}

tasks.register("task2") {
    println("REGISTER TASK2: This is executed during the configuration phase")
}

tasks.named("task1") {
    println("NAMED TASK1: This is executed during the configuration phase")
    doFirst {
        println("NAMED TASK1 - doFirst: This is executed during the execution phase")
    }
    doLast {
        println("NAMED TASK1 - doLast: This is executed during the execution phase")
    }
}

tasks.named("task2") {
    println("NAMED TASK2: This is executed during the configuration phase")
    doFirst {
        println("NAMED TASK2 - doFirst: This is executed during the execution phase")
    }
    doLast {
        println("NAMED TASK2 - doLast: This is executed during the execution phase")
    }
}

步骤 4. 运行 Gradle 任务

运行task1您在步骤 3 中注册和配置的任务：

$ ./gradlew task1

SETTINGS FILE: This is executed during the initialization phase     (1)

> Configure project :app
BUILD SCRIPT: This is executed during the configuration phase       (2)
REGISTER TASK1: This is executed during the configuration phase     (2)
NAMED TASK1: This is executed during the configuration phase        (2)

> Task :app:task1
NAMED TASK1 - doFirst: This is executed during the execution phase  (3)
NAMED TASK1 - doLast: This is executed during the execution phase   (3)

BUILD SUCCESSFUL in 25s
5 actionable tasks: 3 executed, 2 up-to-date

1	初始化：Gradle 执行`settings.gradle(.kts)`以确定要构建的项目并`Project`为每个项目创建一个对象。
2	配置：Gradle 通过执行`build.gradle(.kts)`文件来配置每个项目。它解决依赖关系并创建所有可用任务的依赖关系图。
3	执行：Gradle 执行在命令行上传递的任务以及任何先决条件任务。

需要注意的是，虽然task1已配置并执行，但task2并未配置和执行。这称为任务配置避免并防止不必要的工作。

任务配置避免是指 Gradle 避免配置task2何时task1被调用且不task1依赖。在task2。

下一步： 多项目构建>>

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