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Gradle Wrapper是gradle建议的使用方式，这篇文章将会结合具体的例子来说明一下如何使用。

Gradle Wrapper

Gradle Wrapper实际上就是一个脚本，使用它可以下载和使用指定版本的gradle，根据需要进行在使用之前进行下载，有效避免本地机器的设定等环境一致性问题。
虽然gradle的安装已经非常简单，但是使用gradle wrapper是的开发这能够以一种更为标准化的方式创建gradle项目。

使用方式

Gradle Wrapper的使用方式主要是按照如下步骤：

Step 1: 下载gradle
Step 2: 将下载的gradle解压并存储至GRADLE_USER_HOME所指定的目录
Step 3: 使用解压的gradle

事前准备

使用下面的代码示例，内容不再说明，具体说明信息请参看：

https://blog.csdn.net/liumiaocn/article/details/84230280

liumiaocn:wrapper liumiao$ ls
build.gradle
liumiaocn:wrapper liumiao$ cat build.gradle 
println "[phase:configuration] build.gradle ..."task compile {group 'compile'description 'compile task'println "[phase:configuration] compile"doFirst {println "[phase:execution] compile :doFirst()"}
}tasks.create(name: 'test',dependsOn: compile) {group 'test'description 'test task'println "[phase:configuration] test"doLast {println "[phase:execution] test:doLast()"}
}tasks.create("packaging") {group 'packaging'description 'packaging task'dependsOn testenabled   trueprintln "[phase:configuration] packaging"doLast {println "[phase:execution] packaging:doLast()"}
}class Install extends DefaultTask{String installObjectName@TaskActionvoid checkObject() {println "[phase:execution] install:checkObject   (${installObjectName})"}@TaskActionvoid installObject() {println "[phase:execution] install:installObject (${installObjectName})"}
}task install(type: Install) {group 'install'description 'install task'installObjectName 'test.jar'println "[phase:configuration] install"doFirst {println "[phase:execution] install:doFirst()"}doLast {println "[phase:execution] install:doLast()"}
}
install.dependsOn packaging
install.onlyIf { packaging.enabled }
liumiaocn:wrapper liumiao$

gradle wrapper

通过gradle tasks可以确认到在Build Setup tasks中有wrapper这样一个内建的任务。

liumiaocn:wrapper liumiao$ gradle tasks
...省略
------------------------------------------------------------
All tasks runnable from root project
------------------------------------------------------------Build Setup tasks
-----------------
init - Initializes a new Gradle build.
wrapper - Generates Gradle wrapper files.
...省略
BUILD SUCCESSFUL in 0s
1 actionable task: 1 executed
liumiaocn:wrapper liumiao$

wrapper的说明是这个任务是用来创建gradle wrapper文件，接下里我们来看一下具体创建了那些文件

liumiaocn:wrapper liumiao$ ls
build.gradle
liumiaocn:wrapper liumiao$ gradle wrapper> Configure project :
[phase:configuration] build.gradle ...
[phase:configuration] compile
[phase:configuration] test
[phase:configuration] packaging
[phase:configuration] installBUILD SUCCESSFUL in 0s
1 actionable task: 1 executed
liumiaocn:wrapper liumiao$ ls
build.gradle gradle       gradlew      gradlew.bat
liumiaocn:wrapper liumiao$ tree
.
├── build.gradle
├── gradle
│   └── wrapper
│       ├── gradle-wrapper.jar
│       └── gradle-wrapper.properties
├── gradlew
└── gradlew.bat2 directories, 5 files
liumiaocn:wrapper liumiao$

文件说明：

gradlew：linux或者Unix下用于执行wrapper命令的Shell脚本
gradlew.bat：Windows下用于执行wrapper命令的批处理脚本
gradle-wrapper.jar：用于下载Gradle的相关代码实现
gradle-wrapper.properties：wrapper所使用的配置信息，比如gradle的版本等信息

缺省状况下的gradle-wrapper.properties的信息如下

liumiaocn:wrapper liumiao$ cat gradle/wrapper/gradle-wrapper.properties 
distributionBase=GRADLE_USER_HOME
distributionPath=wrapper/dists
distributionUrl=https\://services.gradle.org/distributions/gradle-4.10.2-bin.zip
zipStoreBase=GRADLE_USER_HOME
zipStorePath=wrapper/dists
liumiaocn:wrapper liumiao$

GRADLE_USER_HOME可以通过环境变量的方式设定，缺省的GRADLE_USER_HOME为 ${HOME}/.gradle，根据这里的信息可以看到，下载的gradle将会解压到$ {HOME}/.gradle/wrapper/dists

使用场景

当前系统安装的gradle的版本为4.10.2，但是在当前的project里面希望使用5.0的gradle，这时gradle wrapper就可以一显身手了

事前确认

当前gradle的版本为4.10.2

liumiaocn:wrapper liumiao$ gradle -v------------------------------------------------------------
Gradle 4.10.2
------------------------------------------------------------Build time:   2018-09-19 18:10:15 UTC
Revision:     b4d8d5d170bb4ba516e88d7fe5647e2323d791ddKotlin 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_64liumiaocn:wrapper liumiao$

设定wrapper使用的gradle版本

可以使用命令来修改wrapper所使用的gradle版本信息

liumiaocn:wrapper liumiao$ gradle wrapper --gradle-version 5.0-rc-5 --distribution-type bin
Starting a Gradle Daemon (subsequent builds will be faster)> Configure project :
[phase:configuration] build.gradle ...
[phase:configuration] compile
[phase:configuration] test
[phase:configuration] packaging
[phase:configuration] installBUILD SUCCESSFUL in 3s
1 actionable task: 1 executed
liumiaocn:wrapper liumiao$

可以看到，实际这条命令只是修改了gradle wrapper的配置文件的下载文件的信息

liumiaocn:wrapper liumiao$ cat gradle/wrapper/gradle-wrapper.properties 
distributionBase=GRADLE_USER_HOME
distributionPath=wrapper/dists
distributionUrl=https\://services.gradle.org/distributions/gradle-5.0-rc-5-bin.zip
zipStoreBase=GRADLE_USER_HOME
zipStorePath=wrapper/dists
liumiaocn:wrapper liumiao$

当然设定也可以通过gradle-distribution-url选项或者直接修改配置文件来更快实现，至于具体版本，gradle的安装文件包符合：
gradle-版本信息-bin|all.zip的格式，按照这种格式即可
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wrapper使用

只需要设定下载url所指定的gradle版本信息，wrapper的准备就已经就绪，随便使用任何一个wrapper的命令，第一次执行都会首先下载gradle并解压到${HOME}/.gradle/wrapper/dists，在在执行之前我们可以看到目前还没有任何内容

liumiaocn:wrapper liumiao$ ls
build.gradle gradle       gradlew      gradlew.bat
liumiaocn:wrapper liumiao$ ls ${HOME}/.gradle/wrapper/dists
ls: /Users/liumiao/.gradle/wrapper/dists: No such file or directory
liumiaocn:wrapper liumiao$

gradle wrapper之所以有被叫做wrapper，就是因为封了一层，所以gradle的基本命令在这里都可以使用，这里直接使用上文确认gradle版本所用的-v

liumiaocn:wrapper liumiao$ ./gradlew -v
Downloading https://services.gradle.org/distributions/gradle-5.0-rc-5-bin.zip
.................................................................................Welcome to Gradle 5.0-rc-5!Here are the highlights of this release:- Kotlin DSL 1.0- Task timeouts- Dependency alignment aka BOM support- Interactive `gradle init`For more details see https://docs.gradle.org/5.0-rc-5/release-notes.html------------------------------------------------------------
Gradle 5.0-rc-5
------------------------------------------------------------Build time:   2018-11-22 19:58:45 UTC
Revision:     42e59c2484a49702234030881640aa8d8bfa6d43Kotlin DSL:   1.0.4
Kotlin:       1.3.10
Groovy:       2.5.4
Ant:          Apache Ant(TM) version 1.9.13 compiled on July 10 2018
JVM:          1.8.0_191 (Oracle Corporation 25.191-b12)
OS:           Mac OS X 10.14 x86_64liumiaocn:wrapper liumiao$

所以看到第一次执行有Downloading https://services.gradle.org/distributions/gradle-5.0-rc-5-bin.zip的动作，而具体的版本正是之前所设定的，gradle的下载和解压对我们来说都是透明的，为什么wrapper能找到这个5.0的版本呢

liumiaocn:wrapper liumiao$ ls ${HOME}/.gradle/wrapper/dists
gradle-5.0-rc-5-bin
liumiaocn:wrapper liumiao$

可以看到，wrapper把它下载并解压到这里了，当然也可以使用系统已经安装的gradle，这种方式直接设定GRADLE_USER_HOME即可。而且下载和设定的动作只会发生一次，除非你手动再次将其删除，现在再次使用gradlew就会清晰的多了

liumiaocn:wrapper liumiao$ ./gradlew -v------------------------------------------------------------
Gradle 5.0-rc-5
------------------------------------------------------------Build time:   2018-11-22 19:58:45 UTC
Revision:     42e59c2484a49702234030881640aa8d8bfa6d43Kotlin DSL:   1.0.4
Kotlin:       1.3.10
Groovy:       2.5.4
Ant:          Apache Ant(TM) version 1.9.13 compiled on July 10 2018
JVM:          1.8.0_191 (Oracle Corporation 25.191-b12)
OS:           Mac OS X 10.14 x86_64liumiaocn:wrapper liumiao$

接下来就可以想使用gradle一样使用gradlew了，比如需要执行install的任务

liumiaocn:wrapper liumiao$ ./gradlew install
Starting a Gradle Daemon (subsequent builds will be faster)> Configure project :
[phase:configuration] build.gradle ...
[phase:configuration] compile
[phase:configuration] test
[phase:configuration] packaging
[phase:configuration] install> Task :compile
[phase:execution] compile :doFirst()> Task :test
[phase:execution] test:doLast()> Task :packaging
[phase:execution] packaging:doLast()> Task :install
[phase:execution] install:doFirst()
[phase:execution] install:installObject (test.jar)
[phase:execution] install:checkObject   (test.jar)
[phase:execution] install:doLast()BUILD SUCCESSFUL in 3s
4 actionable tasks: 4 executed
liumiaocn:wrapper liumiao$

可以看到同样的脚本在gradle 5中也能正常运行