第2部分：构建生命周期 - Gradle 构建系统

了解Gradle构建生命周期以及每个阶段的含义。

在本节中，您将

了解构建生命周期
注册和配置两个任务
运行任务以查看实际运行中的阶段

步骤0. 开始之前

你已在第一部分中初始化了你的 Java 应用程序。

步骤1. 了解构建生命周期

Gradle构建有三个不同的阶段

阶段1 - 初始化: 在初始化阶段，Gradle确定哪些项目将参与构建，并为每个项目创建一个Project实例。
阶段2 - 配置: 在配置阶段，使用构建中所有项目的构建脚本来配置Project对象。Gradle确定要执行的任务集。
阶段3 - 执行: 在执行阶段，Gradle执行每个选定的任务。

当调用Gradle执行任务时，生命周期就开始了。让我们看看它的实际运行。

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

运行您在步骤3中注册和配置的task1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)`来确定要构建的项目，并为每个项目创建一个`Project`对象。
2	配置：Gradle通过执行`build.gradle(.kts)`文件来配置每个项目。它解析依赖项并创建所有可用任务的依赖图。
3	执行：Gradle执行命令行上传递的任务以及任何先决任务。

需要注意的是，虽然task1已配置并执行，但task2却没有。这被称为任务配置避免，可防止不必要的工作。

任务配置避免是指当调用task1时，如果task1不依赖于task2，Gradle会避免配置task2。

下一步： 多项目构建 >>

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