<chapter id='gradle_wrapper' xmlns:xi="http://www.w3.org/2001/XInclude">
    <title>The Gradle Wrapper</title>
    <para>Gradle is a new tool. You can't expect it to be installed on machines beyond your sphere of influence. An
        example are continuous integration server where Gradle is not installed and where you have no admin rights for
        the machine. Or what if you provide an open source project and you want to make it as easy as possible for your
        users to build it?
    </para>
    <para>There is a simple and good news. Gradle provides a solution for this. It ships with a
        <emphasis>Wrapper</emphasis>
        task.
        <footnote>
            <para>If you download the Gradle source distribution or check out Gradle from SVN, you can build Gradle via
                the Gradle wrapper.
            </para>
        </footnote>
        <footnote>
            <para>Gradle itself is continuously built by Bamboo and Teamcity via this wrapper. See
                <ulink url='http://gradle.org/ci-server.html'/>
            </para>
        </footnote>
        You can create such a task in your build script.
    </para>
    <sample id="wrapperSimple" dir="userguide/wrapper" title="Wrapper task">
        <sourcefile file="build.gradle" snippet="wrapper-simple"/>
    </sample>
    <para>The build master usually explicitly executes this task. After such
        an execution you find the following new or updated files in your project folder (in case the default configuration of the wrapper task is
        used).
    </para>
    <screen><![CDATA[
project-root/
  gradlew
  gradlew.bat
  gradle-wrapper.jar
  gradle-wrapper.properties
]]></screen>
    <para>All these files must be submitted to your version control system. The <command>gradlew</command> command
        can be used <emphasis>exactly</emphasis> the same way as the <command>gradle</command> command.
    </para>
    <para>If you want to switch to a new version of Gradle you don't need to rerun the wrapper task. It is good enough
        to change the respective entry in the <literal>gradle-wrapper.properties</literal> file. But if there is for
        example an improvement in the gradle-wrapper functionality you need to regenerate the wrapper files.
    </para>
    <section id='sec:configuration'>
        <title>Configuration</title>
        <para>If you run Gradle with <command>gradlew</command>, Gradle checks if a Gradle distribution for the wrapper
            is available. If not it tries to download it, otherwise it delegates to the <command>gradle</command>
            command of this distribution with all the arguments passed originally to the <command>gradlew</command>
            command.
        </para>
        <para>You can specify where the wrapper files should be stored (within your project directory):</para>
        <sample id="wrapperCustomized" dir="userguide/wrapper" title="Configuration of wrapper task">
            <sourcefile file="build.gradle"/>
        </sample>
        <screen><![CDATA[
project-root/
  gradlew
  gradlew.bat
  wrapper/
    gradle-wrapper.jar
    gradle-wrapper.properties
]]></screen>
        <para>
            You can specify the download URL of the wrapper distribution. You can also specify where the wrapper distribution
            should be stored and unpacked (either within the project or within the gradle user home dir). If the wrapper
            is run and there is local archive of the wrapper distribution Gradle tries to download it and stores it at
            the specified place. If there is no unpacked wrapper distribution Gradle unpacks the local archive of the
            wrapper distribution at the specified place. All the configuration options have defaults except the version of the wrapper distribution.</para>
        <para>For the details on how to configure the wrapper, see <apilink class="org.gradle.api.tasks.wrapper.Wrapper"/>
        </para>
        <para>If you don't
            want any download to happen when your project is build via <command>gradlew</command>, simply add the Gradle
            distribution zip to your version control at the location specified by your wrapper configuration.
        </para>
        <para>If you build via the wrapper, any existing Gradle distribution installed on the machine is ignored.
        </para>
    </section>
    <section id='sec:unix_file_permissions'>
        <title>Unix file permissions</title>
        <para>The Wrapper task adds appropriate file permissions to allow the execution for the gradlew *NIX command.
            Subversion preserves this file permission. We are not sure how other version control systems deal with this.
            What should always work is to execute <literal>sh gradlew</literal>.
        </para>
    </section>
    <section id='sec:environment_variable'>
        <title>Environment variable</title>
        <para>Some rather exotic use cases might occur when working with the Gradle Wrapper. For example the continuos
            integration server goes down during unzipping the Gradle distribution. As the distribution directory exists
            <command>gradlew</command>
            delegates to it but the distribution is corrupt. Or the zip-distribution was not properly downloaded. When
            you have no admin right on the continuous integration server to remove the corrupt files, Gradle offers a
            solution via environment variables.
        </para>
        <table>
            <title>Gradle wrapper environment variables</title>
            <thead>
                <tr>
                    <td>Variable Name</td>
                    <td>Meaning</td>
                </tr>
            </thead>
            <tr>
                <td>GRADLE_WRAPPER_ALWAYS_UNPACK</td>
                <td>If set to <literal>true</literal>, the distribution directory gets always deleted when
                    <command>gradlew</command>
                    is run and the distribution zip is freshly unpacked. If the zip is not there, Gradle tries to
                    download it.
                </td>
            </tr>
            <tr>
                <td>GRADLE_WRAPPER_ALWAYS_DOWNLOAD</td>
                <td>If set to <literal>true</literal>, the distribution directory and the distribution zip gets always
                    deleted when <command>gradlew</command>
                    is run and the distribution zip is freshly downloaded.
                </td>
            </tr>

        </table>
    </section>
</chapter>
