# Chapter 10. Tutorial - 'This and That'

## 10.1. Skipping tasks

Gradle offers multiple ways to skip the execution of a task.

You can set system property named `skip.taskname` or pass such property as a parameter to the gradle command using `-D` option (see Section 10.3, “Gradle properties and system properties”).

Example 10.1. Skipping tasks using default property name

`build.gradle`

    task autoskip << {
        println 'This should not be printed if the skip.autoskip system property is set.'
    }

Output of `gradle -Dskip.autoskip autoskip`

    > gradle -Dskip.autoskip autoskip
    :autoskip SKIPPED

    BUILD SUCCESSFUL

    Total time: 1 secs

You can also choose another another property that can be used to skip a task.

Example 10.2. Skipping tasks using custom property

`build.gradle`

    task skipMe << {
        println 'This should not be printed if the mySkipProperty system property is set to true.'
    }
    skipMe.skipProperties << 'mySkipProperty'

Output of `gradle -DmySkipProperty skipMe`

    > gradle -DmySkipProperty skipMe
    :skipMe SKIPPED

    BUILD SUCCESSFUL

    Total time: 1 secs

You can use this to add one or more skip properties to any task.

In both cases if the corresponding system property is set to any value [6] except false (case does not matter), the actions of the task don't get executed.

### 10.1.1. Skipping depending tasks

By default tasks that depends on skipped task get executed. If you want to skip them, you have to declare this explicitly via the skip properties.

Example 10.3. Skipping depending tasks

`build.gradle`

    task autoskip << {
        println 'This should not be printed if the skip.autoskip system property is set.'
    }
    task depends(dependsOn: autoskip) << {
        println "This should not be printed if the skip.autoskip system property is set."
    }
    depends.skipProperties << 'skip.autoskip'

Output of `gradle -Dskip.autoskip depends`

    > gradle -Dskip.autoskip depends
    :autoskip SKIPPED
    :depends SKIPPED

    BUILD SUCCESSFUL

    Total time: 1 secs

### 10.1.2. Using StopExecutionException

If the rules for skipping a task can't be expressed with a simple property, you can use the `StopExecutionException` . If this exception is thrown by an action, the further execution of this action as well as the execution of any following action of this task is skipped. The build continues with executing the next task.

Example 10.4. Skipping tasks with StopExecutionException

`build.gradle`

    task compile << {
        println 'We are doing the compile.'
    }

    compile.doFirst {
        // Here you would put arbitrary conditions in real life. But we use this as an integration test, so we want defined behavior.
        if (true) { throw new StopExecutionException() }
    }
    task myTask(dependsOn: 'compile') << {
       println 'I am not affected'
    }

Output of `gradle -q myTask`

    > gradle -q myTask
    I am not affected

This feature is helpful if you work with tasks provided by Gradle. It allows you to add conditional execution of the built-in actions of such a task.

You might be wondering why there is neither an import for the `StopExecutionException` nor do we access it via its fully qualified name. The reason is, that Gradle adds a set of default imports to your script. These imports are customizable (see Appendix C, Existing IDE Support and how to cope without it).

### 10.1.3. Enabling and disabling tasks

Every task has also an `enabled` flag which defaults to `true`. Setting it to `false` prevents the execution of any of the task's actions.

Example 10.5. Enabling and disabling tasks

`build.gradle`

    task disableMe << {
        println 'This should not be printed if the task is disabled.'
    }
    disableMe.enabled = false

Output of `gradle disableMe`

    > gradle disableMe
    :disableMe SKIPPED

    BUILD SUCCESSFUL

    Total time: 1 secs

## 10.2. Directory creation

There is a common situation, that multiple tasks depend on the existence of a directory. Of course you can deal with this by adding a `mkdir` to the beginning of those tasks. But this is kind of bloated. There is a better solution (works only if the tasks that need the directory have a dependsOn relationship):

Example 10.6. Directory creation with mkdir

`build.gradle`

    classesDir = new File('build/classes')
    task resources << {
        classesDir.mkdirs()
        // do something
    }
    task compile(dependsOn: 'resources') << {
        if (classesDir.isDirectory()) {
            println 'The class directory exists. I can operate'
        }
        // do something
    }

Output of `gradle -q compile`

    > gradle -q compile
    The class directory exists. I can operate

But Gradle offers you also Directory Tasks to deal with this.

Example 10.7. Directory creation with Directory tasks

`build.gradle`

    classes = dir('build/classes')
    task resources(dependsOn: classes) << {
        // do something
    }
    task otherResources(dependsOn: classes) << {
        if (classes.dir.isDirectory()) {
            println 'The class directory exists. I can operate'
        }
        // do something
    }

Output of `gradle -q otherResources`

    > gradle -q otherResources
    The class directory exists. I can operate

A Directory Task is a simple task whose name is a relative path to the project dir [7] . During the execution phase the directory corresponding to this path gets created if it does not exist yet. Another interesting thing to note in this example, is that you can also pass tasks objects to the dependsOn declaration of a task.

## 10.3. Gradle properties and system properties

Gradle offers a variety of ways to add properties to your build. With the `-D` command line option you can pass a system property to the JVM which runs Gradle. The `-D` option of the gradle command has the same effect as the `-D` option of the java command.

You can also directly add properties to your project objects using properties files. You can place a `gradle.properties` file in the Gradle user home directory (defaults to ``USER_HOME`/.gradle`) or in your project directory. For multi-project builds you can place `gradle.properties` files in any subproject directory. The properties of the `gradle.properties` can be accessed via the project object. The properties file in the user's home directory has precedence over property files in the project directories.

You can also add properties directly to your project object via the `-P` command line option. For more exotic use cases you can even pass properties directly to the project object via system and environment properties. For example if you run a build on a continuous integration server where you have no admin rights for the machine. Your build script needs properties which values should not be seen by others. Therefore you can't use the `-P` option. In this case you can add an environment property in the project administration section (invisible to normal users). [8] If the environment property follows the pattern `ORG_GRADLE_PROJECT_`propertyName`=somevalue`, `propertyName` is added to your project object. If in the future CI servers support Gradle directly, they might start Gradle via its main method. Therefore we already support the same mechanism for system properties. The only difference is the pattern, which is `org.gradle.project.`propertyName`` .

With the `gradle.properties` files you can also set system properties. If a property in such a file has the prefix `systemProp.` the property and its value are added to the system properties, without the prefix.

Example 10.8. Setting properties with a gradle.properties file

`gradle.properties`

    gradlePropertiesProp=gradlePropertiesValue
    systemPropertiesProp=shouldBeOverWrittenBySystemProp
    envPropertiesProp=shouldBeOverWrittenByEnvProp
    systemProp.system=systemValue

`build.gradle`

    task printProps << {
        println commandLineProjectProp
        println gradlePropertiesProp
        println systemProjectProp
        println envProjectProp
        println System.properties['system']
    }

Output of `gradle -q -PcommandLineProjectProp=commandLineProjectPropValue -Dorg.gradle.project.systemProjectProp=systemPropertyValue printProps`

    > gradle -q -PcommandLineProjectProp=commandLineProjectPropValue -Dorg.gradle.project.systemProjectProp=systemPropertyValue printProps
    commandLineProjectPropValue
    gradlePropertiesValue
    systemPropertyValue
    envPropertyValue
    systemValue

### 10.3.1. Checking for project properties

You can access a project property in your build script simply by using its name as you would use a variable. In case this property does not exists, an exception is thrown and the build fails. If your build script relies on optional properties the user might set for example in a gradle.properties file, you need to check for existence before you can access them. You can do this by using the method `hasProperty('propertyName')` which returns `true` or `false`.

## 10.4. Accessing the web via a proxy

Setting a proxy for web access (for example for downloading dependencies) is easy. Gradle does not need to provide special functionality for this. The JVM can be instructed to go via proxy by setting certain system properties. You could set these system properties directly in your build script with `System.properties['proxy.proxyUser'] = 'userid'`. An arguably nicer way is shown in Section 10.3, “Gradle properties and system properties”. Your gradle.properties file could look like this:

Example 10.9. Accessing the web via a proxy

`gradle.properties`

    systemProp.http.proxyHost=http://www.somehost.org
    systemProp.http.proxyPort=8080
    systemProp.http.proxyUser=userid
    systemProp.http.proxyPassword=password

We could not find a good overview for all possible proxy settings. The best we can offer are the constants in a file from the ant project. Here a link to the svn view. If anyone knows a better overview please let us know via the mailing list.

## 10.5. Caching

To improve the responsiveness Gradle caches the compiled build script by default. The first time you run a build for a project, Gradle creates a `.gradle` directory in which it puts the compiled build script. The next time you run this build, Gradle uses the compiled build script, if the timestamp of the compiled script is newer than the timestamp of the actual build script. Otherwise the build script gets compiled and the new version is stored in the cache. If you run Gradle with the `-x` option, any existing cache is ignored and the build script is compiled and executed on the fly. If you run Gradle with the `-r` option, the build script is always compiled and stored in the cache. That way you can always rebuild the cache if for example the timestamps for some reasons don't reflect that the build script needs to be recompiled.

## 10.6. Configuring arbitrary objects

You can configure arbitrary objects in the following very readable way.

Example 10.10. Configuring arbitrary objects

`build.gradle`

    task configure << {
        pos = configure(new java.text.FieldPosition(10)) {
            beginIndex = 1
            endIndex = 5
        }
        println pos.beginIndex
        println pos.endIndex
    }

Output of `gradle -q configure`

    > gradle -q configure
    1
    5

[6] The statement `-Dprop` sets the property to empty string, thus you don't need to type more to skip a task.

[7] The notation `dir('/somepath')` is a convenience method for `tasks.add('somepath', type: Directory)`

[8] Teamcity or Bamboo are for example CI servers which offer this functionality.