基于groovy语言的DSL编程基础（项目构建）

Gradle是一种基于依赖的编程语言，你可以在已有的task中自定义task或者依赖规则。对比我们最常用的语言，比如java、Object-C，Gradle就像同时包含了配置虚拟机、字节码解释规则、code语法。Gradle会让这些task按照顺序执行，且只执行一次。有些build tools工具会在任何一个task执行前构建完成一个基于依赖的task队列，便于完成它指定的编译任务，比如com.android.tools.build。

一次Gradle构建包含三个阶段：Initialization（初始化）、Configuration（配置）、Execution（运行）

1）Initialization

Gradle支持同时至少一个项目的构建，在Initialization阶段，Gradle决定哪个项目可以参与构建（build），并为它们分别创建一个Project实例。

2）Configuration

参与构建的所有项目的build script会被执行（从Gradle 1.4开始，有关联的项目才会被配置）

3）Execution

Gradle划分完成在配置阶段被创建的即将执行的task，通过gradle命令参数和当前目录确定这些task是否应该得到执行。

Setting文件

Gradle确定一个默认名为setting.gradle的setting文件，这个文件会在Initialization阶段执行。同时构建多个项目时，必须在所有项目的顶层目录中放置一个setting.gradle文件，这个文件用来确定哪个项目参与接下来的构建过程。如果只有个项目，可以没有setting.gradle文件。

单项目构建举例：

settings.gradle

println 'This is executed during the initialization phase.'

build.gradle

println 'This is executed during the configuration phase.'task configured {    println 'This is also executed during the configuration phase.'}task test << {    println 'This is executed during the execution phase.'}task testBoth {    doFirst {      println 'This is executed first during the execution phase.'    }    doLast {      println 'This is executed last during the execution phase.'    }    println 'This is executed during the configuration phase as well.'}

运行命令：gradle test testBoth

> gradle test testBothThis is executed during the initialization phase.This is executed during the configuration phase.This is also executed during the configuration phase.This is executed during the configuration phase as well.:testThis is executed during the execution phase.:testBothThis is executed first during the execution phase.This is executed last during the execution phase.BUILD SUCCESSFULTotal time: 1 secs

附注：在一段Gradle脚本中，可以通过一个project对象实现对属性的访问和方法的调用。同样的，在setting文件中，可以通过setting(比如Setting类对象)对象实现对属性的访问和方法的调用。