Gradle基础：2:Gradle的HelloWorld

gradle
这篇文章使用最简单的HelloWorld例子对Gradle的使用进行概要性的说明。

事前准备

事前安装和设定好gradle

liumiaocn:hello liumiao$ gradle --version

------------------------------------------------------------
Gradle 4.10.2
------------------------------------------------------------

Build time:   2018-09-19 18:10:15 UTC
Revision:     b4d8d5d170bb4ba516e88d7fe5647e2323d791dd

Kotlin DSL:   1.0-rc-6
Kotlin:       1.2.61
Groovy:       2.4.15
Ant:          Apache Ant(TM) version 1.9.11 compiled on March 23 2018
JVM:          1.8.0_191 (Oracle Corporation 25.191-b12)
OS:           Mac OS X 10.14 x86_64

liumiaocn:hello liumiao$

第一个HelloWorld

准备一个groovy文件，具体信息如下

liumiaocn:hello liumiao$ ls
build.gradle
liumiaocn:hello liumiao$ cat build.gradle 
println "hello gradle"
liumiaocn:hello liumiao$

执行gradle命令

liumiaocn:hello liumiao$ gradle

> Configure project :
hello gradle

> Task :help

Welcome to Gradle 4.10.2.

To run a build, run gradle <task> ...

To see a list of available tasks, run gradle tasks

To see a list of command-line options, run gradle --help

To see more detail about a task, run gradle help --task <task>

For troubleshooting, visit https://help.gradle.org

BUILD SUCCESSFUL in 0s
1 actionable task: 1 executed
liumiaocn:hello liumiao$

这个例子看起来更像是groovy的hello world，接下来先对gradle的基本概念等信息进行展开后，对此例子再进行进一步地解释。

基础概念

Gradle有两个最基础的概念：

Task：在构建中Gradle执行和管理的原子粒度的最小单元，比如上例中的输出hello的语句，在实际的使用中比如编译或者执行单体测试等操作均可作为task。
Project：可以理解为Project就是存放Task的场所，Project可由一个或多个Task所组成。而构建也可以由多个Project所组成，这样就能实现对不同项目的适应。

两个gradle文件

在例子中使用了一个build.gradle文件，还有一个settings.gradle文件在最初使用时会经常见到：

build.gradle: 用于存放构建相关的Task，单个工程（Project）与build.gradle的关系是一对一的关系，如果是多个工程的情况下，类似与maven的module的方式，构建根目录下的build.gradle起到总纲的作用。
settings.gradle: 用于存放设定相关的信息，单工程时不是必须的，多工程是必须的，一般用于引入多个工程，在项目初期化的时候会根据此文件生成一个Settings实例用于执行。

Projects的确认

使用gradle projects可以查看工程下的详细信息

liumiaocn:hello liumiao$ gradle projects

> Configure project :
hello gradle

> Task :projects

------------------------------------------------------------
Root project
------------------------------------------------------------

Root project 'hello'
No sub-projects

To see a list of the tasks of a project, run gradle <project-path>:tasks
For example, try running gradle :tasks

BUILD SUCCESSFUL in 0s
1 actionable task: 1 executed
liumiaocn:hello liumiao$

可以看到，Root project 'hello’的提示，以及没有子工程（No sub-projects）的提示。

Tasks的确认

通过gradle tasks可以查看task的详细信息

liumiaocn:hello liumiao$ gradle tasks

> Configure project :
hello gradle

> Task :tasks

------------------------------------------------------------
All tasks runnable from root project
------------------------------------------------------------

Build Setup tasks
-----------------
init - Initializes a new Gradle build.
wrapper - Generates Gradle wrapper files.

Help tasks
----------
buildEnvironment - Displays all buildscript dependencies declared in root project 'hello'.
components - Displays the components produced by root project 'hello'. [incubating]
dependencies - Displays all dependencies declared in root project 'hello'.
dependencyInsight - Displays the insight into a specific dependency in root project 'hello'.
dependentComponents - Displays the dependent components of components in root project 'hello'. [incubating]
help - Displays a help message.
model - Displays the configuration model of root project 'hello'. [incubating]
projects - Displays the sub-projects of root project 'hello'.
properties - Displays the properties of root project 'hello'.
tasks - Displays the tasks runnable from root project 'hello'.

To see all tasks and more detail, run gradle tasks --all

To see more detail about a task, run gradle help --task <task>

BUILD SUCCESSFUL in 0s
1 actionable task: 1 executed
liumiaocn:hello liumiao$

改进的HelloWorld

上述的HelloWorld例子过于简单, 在settings.gradle中添加一句println来确认一下执行顺序，然后设定project的名称，而不是使用缺省被指定的hello

liumiaocn:hello liumiao$ cat settings.gradle 
println "setting gradle ..."
rootProject.name='helloPorject'
liumiaocn:hello liumiao$

同样，对task也做一些简单的设定，详细后续在task的使用方式中展开

liumiaocn:hello liumiao$ cat build.gradle 
task helloGradle {
  println "hello gradle"
}
project.task('helloTask',group:'helloGradle',description:'hello gradle task')
liumiaocn:hello liumiao$

确认project

liumiaocn:hello liumiao$ gradle projects
setting gradle ...

> Configure project :
hello gradle

> Task :projects

------------------------------------------------------------
Root project
------------------------------------------------------------

Root project 'helloPorject'
No sub-projects

To see a list of the tasks of a project, run gradle <project-path>:tasks
For example, try running gradle :tasks

BUILD SUCCESSFUL in 0s
1 actionable task: 1 executed
liumiaocn:hello liumiao$

确认task

liumiaocn:hello liumiao$ gradle tasks
setting gradle ...

> Configure project :
hello gradle

> Task :tasks

------------------------------------------------------------
All tasks runnable from root project
------------------------------------------------------------

Build Setup tasks
-----------------
init - Initializes a new Gradle build.
wrapper - Generates Gradle wrapper files.

HelloGradle tasks
-----------------
helloTask - hello gradle task

Help tasks
----------
buildEnvironment - Displays all buildscript dependencies declared in root project 'helloPorject'.
components - Displays the components produced by root project 'helloPorject'. [incubating]
dependencies - Displays all dependencies declared in root project 'helloPorject'.
dependencyInsight - Displays the insight into a specific dependency in root project 'helloPorject'.
dependentComponents - Displays the dependent components of components in root project 'helloPorject'. [incubating]
help - Displays a help message.
model - Displays the configuration model of root project 'helloPorject'. [incubating]
projects - Displays the sub-projects of root project 'helloPorject'.
properties - Displays the properties of root project 'helloPorject'.
tasks - Displays the tasks runnable from root project 'helloPorject'.

To see all tasks and more detail, run gradle tasks --all

To see more detail about a task, run gradle help --task <task>

BUILD SUCCESSFUL in 0s
1 actionable task: 1 executed
liumiaocn:hello liumiao$

执行task

task既然有名称了，就可以使用名称来执行了

liumiaocn:hello liumiao$ gradle helloGradle
setting gradle ...

> Configure project :
hello gradle

BUILD SUCCESSFUL in 0s
liumiaocn:hello liumiao$

总结

Task和Project两个基本概念，settings.gradle和build.gradle两个缺省配置文件，这是需要首先掌握的。