Built by Maven

Usage

Wrapper scripts are a set of files that can be added to your Maven project. If people want to build this project, they don't need to install Maven first. Instead they can call the Maven wrapper script (like mvnw/mvnw.cmd), which will download and unpack Maven into their ${user.home}/.m2/wrapper/dists folder. It is also an easy way to let everyone build the project with the same Maven version.

The Apache Maven Wrapper Plugin makes it easier to add these wrapper scripts to your project.

The scripts work like this:

  • download the maven-wrapper jar, if it is not available yet,
  • the maven-wrapper.jar contains the code to download, install and run Apache Maven

Apache Maven Wrapper Distribution Types

There are 4 distribution types available:

  • only-script (default for new installations): the lite implementation of mvnw/mvnw.cmd scripts will download the maven directly via wget or curl on *nix, or PowerShell on Windows, then exec/call the original mvn/mvn.cmd scripts of the downloaded maven distribution. This type does not use maven-wrapper.jar nor MavenWrapperDownloader.java, only the wrapper scripts are required.

  • script: With this type the scripts will try to download the scripts via wget or curl in case of Unix based system, or use Powershell in case of Windows

  • bin: With this type the maven-wrapper jar is already available in the .mvn/wrapper folder, so you don't have to rely on wget/curl or Powershell The downside is that the project will contain a binary file in the source control management system.

  • source: Since Maven already requires Java to run, why not compile and run a classfile to download the maven-wrapper jar? This type comes with a .mvn/wrapper/MavenWrapperDownloader.java which will be compiled and executed on the fly.

The type can be specified with mvn wrapper:wrapper -Dtype={type}, where {type} is any of the types listed above.

When wrapper:wrapper is run in a Maven module which contains a .mvn/wrapper/maven-wrapper.properties file, then the distribution type of the existing Maven Wrapper is used for the execution of the goal. This allows updating Maven Wrapper, without unintentionally changing the distribution type for an existing project. You can still use -Dtype={type} to change the distribution type for an existing installation.

Maven Version

By default the plugin will assume the same version as the Maven runtime (calling mvn -v). But you can pick a different version. You can call mvn wrapper:wrapper -Dmaven=x, where x is any valid Apache Maven Release (see Maven Central). Another option is to adjust the distributionUrl in .mvn/wrapper/maven-wrapper.properties.

Debugging

The apache-maven-wrapper distributions all contains the mvnwDebug-script for both Windows and Unix based operating systems. This makes it possible to debug through Apache Maven, Maven Plugin or Maven Extension. You can include these scripts by calling mvn wrapper:wrapper -DincludeDebug=true