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| # Heroku Cloud Native Maven Buildpack | ||
| # Heroku Cloud Native Maven Buildpack | ||
| [](https://circleci.com/gh/heroku/buildpacks-jvm/tree/main) | ||
| [](https://registry.buildpacks.io/buildpacks/heroku/maven) | ||
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| Heroku's official Cloud Native Buildpack for [Apache Maven](https://maven.apache.org/). | ||
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| This buildpack is designed to work in conjunction with other Heroku buildpacks and cannot be used independently. If you | ||
| want to build a Java application, use the `heroku/java` buildpack ([Source](/meta-buildpacks/java), | ||
| [Readme](/meta-buildpacks/java/README.md)) which includes this Maven buildpack. | ||
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| ## How it works | ||
| ### Step 1: Download Maven | ||
| If the application does not contain Maven Wrapper, the buildpack will download Maven and install it in its own layer. | ||
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| Users can specify the Maven version for their application by adding (or extending) a | ||
| [Java properties file](https://en.wikipedia.org/wiki/.properties) called `system.properties` in the root directory of | ||
| the application. | ||
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| The `maven.version` key determines the Maven version that is installed. Currently, supported versions are `3.2.5`, | ||
| `3.3.9`, `3.5.3`, and `3.6.2`. The default is `3.6.2`. | ||
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| ### Step 2: Resolve settings.xml | ||
| A Maven `settings.xml` file defines values that configure Maven execution in various ways. Most commonly, it is used to | ||
| define a local repository location, alternate remote repository servers, and authentication information for private | ||
| repositories. | ||
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| When a file named `settings.xml` is present in the root directory of the application, the buildpack will automatically | ||
| use it to configure Maven at build time. The environment variable [MAVEN\_SETTINGS\_PATH](#MAVEN_SETTINGS_PATH) can be | ||
| used customize the file location. | ||
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| In addition, the [MAVEN\_SETTINGS\_URL](#MAVEN_SETTINGS_URL) environment variable can be used to instruct the buildpack | ||
| to download a `settings.xml` file from a remote host via HTTPS. | ||
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| ### Step 3: Run Maven build | ||
| By default, the Maven command used to build the application is `mvn clean install -DskipTests`. Users can customize | ||
| this with the [MAVEN\_CUSTOM\_GOALS](#MAVEN_CUSTOM_GOALS) and [MAVEN\_CUSTOM\_OPTS](#MAVEN_CUSTOM_OPTS) environment | ||
| variables. | ||
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| In addition, some extra configuration is used to ensure Maven stores the local repository in a dedicated layer. | ||
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| ### Step 4: Generate target/mvn-dependency-list.log | ||
| This buildpack will create a `target/mvn-dependency-list.log` in the application directory that can be used to later | ||
| determine which dependencies (including transitive ones) have been installed during the build. | ||
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| ### Step 5: launch.toml | ||
| For applications that use Spring Boot or Wildfly Swarm, this buildpack will generate a `launch.toml` with a `web` process | ||
| type to launch the application. | ||
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| ## Reference | ||
| ### Detect | ||
| Requires either `pom.xml`, `pom.atom`, `pom.clj`, `pom.groovy`, `pom.rb`, `pom.scala`, `pom.yaml`, or `pom.yml` at the | ||
| root of the application source. | ||
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| ### Build Plan | ||
| #### Requires | ||
| ##### `jdk` | ||
| To compile Java sources a JDK is required. It can be provided by the `heroku/jvm` ([Source](/buildpacks/jvm), | ||
| [Readme](/buildpacks/jvm/README.md)) buildpack. | ||
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| ##### `jvm-application` | ||
| This is not a strict requirement of the buildpack. Requiring `jvm-application` ensures that this Maven buildpack can be | ||
| used even when no other buildpack requires `jvm-application.` | ||
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| #### Provides | ||
| ##### `jvm-application` | ||
| Allows other buildpacks to depend on a compiled JVM application. | ||
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| ### Environment Variables | ||
| #### `MAVEN_SETTINGS_PATH` | ||
| If you do not want the `settings.xml` file in the root directory or if you intend to frequently change between different | ||
| setting configurations, you may prefer to put a settings file in a custom location. The buildpack provides this | ||
| capability with the `MAVEN_SETTINGS_PATH` environment variable. | ||
| #### `MAVEN_SETTINGS_URL` | ||
| When the `MAVEN_SETTINGS_URL` config variable is defined, the buildpack will download the file at the given location | ||
| and use it to configure Maven. | ||
| #### `MAVEN_CUSTOM_OPTS` | ||
| Allows overriding Maven options used during the build process. The default options are `-DskipTests`. | ||
| #### `MAVEN_CUSTOM_GOALS` | ||
| Allows overriding the Maven goals used during the build process. The default goals are `clean install`. | ||
| #### `MAVEN_JAVA_OPTS` | ||
| Allows overriding the Java options for the Maven process during build. The default Java options are `-Xmx1024m`. | ||
| #### `HEROKU_BUILDPACK_DEBUG` | ||
| If set, the buildpack will emit debug log messages. | ||
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| ## License | ||
| Licensed under the MIT License. See [LICENSE](../../LICENSE) file. |