在使用maven的時候，compile/test/install的先後順序和依賴關係都十分清晰，而在前面的例子中，可以通過gradle compile和gradle test來進行不同的任務執行，但是實際這些任務之間是有依賴關係的，就像我們在maven裡面執行mvn install之前會做什麼那樣，這篇文章會繼續來介紹task之間的依賴與執行條件。

示例介紹

這篇文章會通過對上文的例子進行重新改寫，來介紹gradle對於task操作的依賴和執行條件，還是如下4個任務：

事前準備

修改之前的程式碼示例如下所示，對前文中的task的<<使用方式進行了修改，以消除warning資訊

• 程式碼示例

liumiaocn:hello 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') {
  group 'test'
  description 'test task'
  println "[phase:configuration] test"
  doLast {
    println "[phase:execution] test:doLast()"
  }
}

tasks.create("packaging") {
  group 'packaging'
  description 'packaging task'
  println "[phase:configuration] packaging"
  doLast {
    println "[phase:execution] packaging:doLast()"
  }
}

class Install extends DefaultTask{
  String installObjectName

  @TaskAction
  void checkObject() {
    println "[phase:execution] install:checkObject   (${installObjectName})"
  }

  @TaskAction
  void 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()"
  }
}
liumiaocn:hello liumiao$
 

• 執行確認

liumiaocn:hello liumiao$ gradle compile test packaging install
[Phase: initialization] : settings executed... 

> 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 0s
4 actionable tasks: 4 executed
liumiaocn:hello liumiao$ 
 

依賴設定

前面準備的例子有一個主要的問題，task之間的依賴關係實際是沒有的，上文顯示的執行順序實際是因為輸入的順序產生的，在gradle裡面也非常容易地通過dependsOn進行依賴關係的設定，這裡將常用的方式進行整理如下：

方式1: 通過()傳入

tasks.create(name: 'test',dependsOn: compile) {
  group 'test'
  description 'test task'
  println "[phase:configuration] test"
  doLast {
    println "[phase:execution] test:doLast()"
  }
}

執行結果確認資訊如下，可以看到test在執行時compile的任務被事先執行了

liumiaocn:hello liumiao$ gradle test
[Phase: initialization] : settings executed... 

> 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()

BUILD SUCCESSFUL in 0s
2 actionable tasks: 2 executed
liumiaocn:hello liumiao$ 

方式2: 在{}中設定

{}中設定的是任務的配置程式碼或者執行階段程式碼的詳細資訊，在這裡可以進行設定，比如：

tasks.create("packaging") {
  group 'packaging'
  description 'packaging task'
  dependsOn test
  println "[phase:configuration] packaging"
  doLast {
    println "[phase:execution] packaging:doLast()"
  }
}

執行結果確認資訊如下，注意由於test任務依賴於compile，所以在執行packaging的時候，會同時執行：

liumiaocn:hello liumiao$ gradle packaging
[Phase: initialization] : settings executed... 

> 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()

BUILD SUCCESSFUL in 0s
3 actionable tasks: 3 executed
liumiaocn:hello liumiao$

方式3: 在{}外設定

當然也可以在{}進行指定，由於在{}之外，缺乏上下文，自然需要指定是誰依賴誰，而不是像前兩種方式那樣只需要設定依賴物件即可。

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

這樣執行起來，依賴關係就完整了。

liumiaocn:hello liumiao$ gradle install
[Phase: initialization] : settings executed... 

> 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 0s
4 actionable tasks: 4 executed
liumiaocn:hello liumiao$ 

程式碼示例

liumiaocn:hello 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 test
  println "[phase:configuration] packaging"
  doLast {
    println "[phase:execution] packaging:doLast()"
  }
}

class Install extends DefaultTask{
  String installObjectName

  @TaskAction
  void checkObject() {
    println "[phase:execution] install:checkObject   (${installObjectName})"
  }

  @TaskAction
  void 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
liumiaocn:hello liumiao$

enable屬性

在前文介紹task常用屬性和方法時，還提及到一個enable屬性，這裡通過示例來演示一下使用方式：

tasks.create("packaging") {
  group 'packaging'
  description 'packaging task'
  dependsOn test
  enabled   false
  println "[phase:configuration] packaging"
  doLast {
    println "[phase:execution] packaging:doLast()"
  }
}

這樣執行起來，由於enabled被設定為false，執行的過程則被跳過了

雖然執行過程被跳過了，但是配置還是會執行的，這個需要注意一下。

liumiaocn:hello liumiao$ gradle install
[Phase: initialization] : settings executed... 

> 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 :install
[phase:execution] install:doFirst()
[phase:execution] install:installObject (test.jar)
[phase:execution] install:checkObject   (test.jar)
[phase:execution] install:doLast()

BUILD SUCCESSFUL in 0s
3 actionable tasks: 3 executed
liumiaocn:hello liumiao$ 

當然使用方式也有很多種，比如也可以使用packaging.enabled = false在{}外設定，這裡就不再贅述了。

onlyIf屬性

onlyIf屬性進行條件判斷，比如install任務根據packaging的enabled是否為true進行判斷當前install任務是否執行的時候，即可加上如下設定即可

install.onlyIf { packaging.enabled }

這樣在執行的時候，packaging的enabled如果是false的話，install也不會執行了

liumiaocn:hello liumiao$ gradle install
[Phase: initialization] : settings executed... 

> 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()

BUILD SUCCESSFUL in 0s
2 actionable tasks: 2 executed
liumiaocn:hello liumiao$ 

程式碼示例

由於演示enabled和onlyIf屬性，程式碼略有變化，再次貼出如下：

liumiaocn:hello 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 test
  enabled   false
  println "[phase:configuration] packaging"
  doLast {
    println "[phase:execution] packaging:doLast()"
  }
}

class Install extends DefaultTask{
  String installObjectName

  @TaskAction
  void checkObject() {
    println "[phase:execution] install:checkObject   (${installObjectName})"
  }

  @TaskAction
  void 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:hello liumiao$

總結

使用gradle的dependsOn/enabled/onlyIf等特性，結合groovy語言進行簡單編碼，gradle能夠實現非常靈活的用法，可以在具體專案中進行不斷實踐。